Problems of modern theory of elementary particles. Abstract: Elementary particles. Electromagnetic model of the neutron

William Gilbert formulated a postulate approximately 400 years ago that can be considered the main postulate of the natural sciences. Despite the fact that in our time it is impossible to find a researcher who would disagree with this statement, a number of modern physical theories do not satisfy this principle.

In the physics of the microworld, there are several generally accepted models that also do not satisfy Hilbert’s postulate. These models do not make it possible to calculate the main characteristic parameters, such as the masses and magnetic moments of elementary particles. This article discusses an alternative approach to solving this problem.

A new approach to the problem of the nature of nuclear forces is considered. It has been shown that attraction in a proton–neutron pair can arise due to the exchange of a relativistic electron. The estimate of the energy of such an exchange is consistent with the experimental value of the binding energy of some light nuclei. In this case, the neutron is considered as a composite particle consisting of a proton and a relativistic electron, which makes it possible to predict its mass, magnetic moment and energy of its decay.

Within the framework of the standard Maxwellian theory of the electromagnetic field, it is shown that it is possible to excite in empty space (ether) a magnetic γ-quantum (magnetic field burst), devoid of an electrical component and having spin ħ / 2. A characteristic feature of such a magnetic γ-quantum is the weakness of its interaction with matter, which is many orders of magnitude smaller than that of an electromagnetic wave. These properties suggest that the magnetic γ-quantum can be identified with the neutrino. On this basis, it is possible to take a new look at the nature of the π-meson, μ-meson and λ-hyperon, calculating their masses and magnetic moment.

1. The main postulate of the natural sciences.

1.1. Hilbert's postulate and modern physics.

2. Proton and neutron.

2.1. Proton and neutron in the Gell-Mann quark model.

2.2. Model of a proton consisting of quarks with an integer charge.

2.3. Physical properties of the neutron.

2.4. Neutron structure.

2.4.1. Electromagnetic model of the neutron.

2.4.2. Basic parameters of the neutron.

2.5. Discussion.

3. On the nature of nuclear forces.

3.1. Molecular hydrogen ion.

3.2. Deuteron.

3.3. Light kernels.

3.3.1. Nucleus 3 2 He.

3.3.2. Nucleus 4 2 He.

3.3.3. Nucleus 6 3 Li.

3.4. Discussion.

4. Neutrinos and mesons.

4.1. Neutrino.

4.2. Mesons.

4.3. Excited state with S = 0.

4.4. Excited state with n= 2 and S = ħ  / 2.

5. Conclusion.

1. The main postulate of natural sciences

To our contemporaries, whose level of education corresponds to the development of science in the 21st century, it may seem that medieval science was concentrated in theology, astrology and alchemy. But this is absolutely not true. The Middle Ages were the time when the foundations of modern science were developed.

The medieval scientist William Gilbert (1544...1603) introduced the concepts of electric and magnetic fields into scientific use, taking the first step towards understanding the nature of electromagnetism. He was the first to try to explain the nature of the Earth's magnetic field. But at the same time, it seems that his most important contribution to science is the principle he developed, which has become the main principle of modern natural science research*.

* It can be assumed that the idea of ​​this principle, as they say, was in the air among educated people of that time. But I found my formulation, which has come down to us, this principle thanks to W. Gilbert.

Hilbert's principle is stated simply:

All theoretical constructs that claim to be scientific must be tested and confirmed experimentally.

There seems to be no one among our modern scientists who would object to this. However, in the twentieth century, a whole series of scientific constructions were created that were accepted by the scientific community and are still dominant in their fields of knowledge, but at the same time they do not satisfy Hilbert’s principle.

1.1. Hilbert's postulate and modern physics

It should be emphasized that the overwhelming majority of modern theoretical models adequately and accurately reflect the properties of matter and the laws of Nature, since at all stages the construction of these theories is carried out in full accordance with the Hilbert principle.

But in a number of cases, the models developed by theorists turned out to be incorrect.

Let's consider some problems of the microworld, in the solution of which Hilbert's principle was violated.

2. Proton and neutron

2.1. Proton and neutron in the Gell-Mann quark model

It seems that specialists in elementary particle physics first proceeded from the assumption that during the creation of the world, each elementary particle was individually selected the appropriate parameters: charge, spin, mass, magnetic moment, etc.

Gell-Mann simplified this work somewhat. He developed a rule according to which the set of quarks determines the total charge and spin of the formed elementary particle. But the masses and magnetic moments of these particles do not fall under this rule.

Rice. 1. Quark structure of the proton and neutron according to Gell-Mann. The charges of quarks are selected so that the transformation of a neutron into a proton is carried out by replacing one d-quark with a u-quark. The Gell-Mann model does not pretend to predict the masses and magnetic moments of the proton and neutron

The Gell-Mann quark model assumes that the quarks that make up all elementary particles (except the lightest) should have a fractional (equal to 1/3 e or 2/3 e) electric charge.

In the 60s, after the formulation of this model, many experimenters tried to find particles with a fractional charge. But unsuccessfully.

In order to explain this, it was assumed that quarks are characterized by confinement, i.e. a property that prohibits them from expressing themselves in any way in a free state. At the same time, it is clear that confinement removes quarks from subordination to the Hilbert principle. In this form, the model of quarks with fractional charges claims to be scientific without confirmation by measurement data.

It should be noted that the quark model successfully describes some experiments on particle scattering at high energies, for example, the formation of jets or the feature of scattering high-energy particles without destruction. However, this does not seem to be enough to recognize the existence of quarks with a fractional charge.

2.2. Model of a proton consisting of quarks with an integer charge

Let us set ourselves the goal of constructing a model of the proton from quarks with an integer charge so that it predicts the mass and magnetic moment of the proton. We will assume that, as in the Gell-Mann model, the proton consists of three quarks. But in our case, two of them have a charge + e and one - e. Let these quarks not have their own spin, and their quantum motion is expressed by their rotation around a common center along a circle of radius R.

Rice. 2.

Let the radius be R is determined by the fact that on the circumference 2π R fits the length of the de Broglie wave of the quark λ D:

The generalized angular momentum (spin) of the system will be composed of two terms: the mechanical angular momentum of all three quarks 3 p q ×  R and the angular momentum of the magnetic field created by a quark with an uncompensated charge \(\frac(e)(c)(\bf(A))\):

and magnetic moment of circular current

here β = v/c.

Based on the fact that the proton spin is equal to ħ / 2, we have

Total mass of three quarks

Taking into account the magnitude of the quark mass (8), the magnetic moment created by it is equal to

2.3. Physical properties of the neutron

In the Gell-Mann quark model, the neutron is assumed to be an elementary particle in the sense that it is composed of a different set of quarks than the proton. In the 30s of the last century, theoretical physicists came to the conclusion about the elementarity of the neutron, without relying on measurement data, which did not exist at that time.

To explain the measurement data of the neutron parameters - the magnetic moment of the neutron, the mass and energy of its decay - let's consider the electromagnetic model of the neutron, in which it is not an elementary particle.

Let us assume that the neutron, like the Bohr hydrogen atom, consists of a proton around which an electron rotates at a very small distance from it. Near the proton, the motion of the electron should be relativistic. However, the peculiarity of the stable orbit that is formed in this case is that when calculating it, all relativistic corrections compensate each other and are completely eliminated.

Let us consider the electromagnetic model of the neutron in more detail.

2.4. Neutron structure

2.4.1. Electromagnetic model of the neutron

In the early days after the discovery of the neutron, the question of whether it should be considered an elementary particle was discussed in physics. There was no experimental data that could help resolve this issue, and soon it was believed that the neutron, like the proton, is an elementary particle. However, the fact that the neutron is unstable and decays into a proton and an electron (+ antineutrino) gives grounds to classify it as a non-elementary compound particle.

Let us consider a compound particle in which around a proton with a speed v → c a particle with rest mass rotates m e and charge - e. (Previously, a similar approach was considered in the works and).

Let us choose a cylindrical coordinate system in which the axis z coincides with the direction of the proton's magnetic moment

Between a positively charged proton and a negatively charged electron there must be a force of Coulomb attraction (, §24):

which manifests itself in the Lorentz force:

and the force created by the magnetic field of the ring tending to break it

The result is an equilibrium equation with unknowns R 0 and β takes the form:

The magnetic field in the system is created by the magnetic moment of the proton

Here α = e 2  / ħc– fine structure constant,

r c = ħ  / m e c– Compton radius.

In order to write down the second equation connecting these parameters, we use the virial theorem. According to this theorem, the kinetic energy of particles united by electromagnetic interaction during their finite motion is equal to half of their potential energy, taken with the opposite sign:

therefore, the second equation connecting these parameters takes the form:

In this case, the magnetic moment of the current ring, expressed in nuclear magnetons μ N

This value agrees well with the measured value of the neutron magnetic moment (ξ n = –1,91304272):

According to the virial theorem, the total energy of the system under consideration should be equal to its kinetic energy (26):

During the decay of a neutron, this energy will be converted into the kinetic energy of the emitted electron (and antineutrino), which is in exact agreement with the experimentally determined limit of the spectrum of decay electrons, equal to 782 keV.

2.5. Discussion

In the proton model considered above, composed of quarks with integral charges, there is no question of the observability of quarks in a free state. However, many unknowns remain.

It is not clear where the magnetic moment of the positron that forms the proton disappears. The magnetic moment of the electron forming the neutron does not manifest itself due to the fact that the spin of the ring current is zero. However, this is not the case with the quark-positron. It is not clear why the quark-positron does not annihilate with the quark-electron, and what interactions force them to combine into a completely stable particle - the proton, the decay of which is not observed in nature.

The obtained agreement between the estimates and the measurement data of the properties of the neutron indicates that it is not an elementary particle. It should be considered as a kind of relativistic analogue of the Bohr hydrogen atom. With the difference that in a Bohr atom the non-relativistic electron is held on the shell by Coulomb forces, and in a neutron the relativistic electron is held mainly due to magnetic interaction. In accordance with Hilbert's postulate, confirmation by experience of the electromagnetic model of the neutron discussed above seems to be a necessary and completely sufficient argument for its reliability.

However, to understand the model, it is important to use generally accepted theoretical apparatus when constructing it. It should be noted that for scientists accustomed to the language of relativistic quantum physics, the methodology used above in making estimates does not, at a quick glance, contribute to the perception of the results obtained. It is generally accepted that, for reliability, the influence of relativism on the behavior of an electron in a Coulomb field should be taken into account within the framework of the Dirac theory. However, in the specific case of calculating the neutron mass, its magnetic moment and decay energy, this is not necessary, since the spin of the electron in the state under consideration is zero and all relativistic effects are described by terms with coefficients \((\left((1 - \frac((( v^2)))(((c^2)))) \right)^( - 1/2))\), compensate each other and drop out completely. The neutron considered in our model is a quantum object, since the radius R 0 is proportional to Planck's constant ħ , but formally it cannot be considered relativistic, because coefficient \((\left((1 - \frac(((v^2)))(((c^2)))) \right)^( - 1/2))\)in the definition R 0 is not included. This makes it possible to calculate the neutron mass, its magnetic moment and decay energy by simply finding the equilibrium parameters of the system from the condition of the balance of forces, as is customary for non-relativistic objects. The situation is different with the assessment of the neutron lifetime. Relativism, apparently, should influence this parameter. Without taking it into account, it is not possible to correctly estimate the neutron lifetime even by order of magnitude.

3. On the nature of nuclear forces

3.1. Molecular hydrogen ion

In 1927, a quantum mechanical description of the simplest molecule, the molecular hydrogen ion, was published. The authors of this article, W. Heitler and F. London, calculated the attraction that arises between two protons due to the exchange of an electron if the state of the molecular ion is described by a double-well potential (Fig. 3). This exchange is a quantum mechanical effect and its classical analogue does not exist. (Some details of this calculation are given in).

The main conclusion of this work is that the binding energy between two protons, arising due to the exchange of an electron, is close in order of magnitude to the binding energy of a proton and an electron (the energy of the electron in the first Bohr orbit). This conclusion is in satisfactory agreement with the measurement data, which give a result that differs from the calculated one by less than two times.

Rice. 3. Schematic representation of a symmetric double-well potential. In the ground state, the electron can be either in the right or left side of the well. In an unperturbed state, its energy is equal to E 0 . Tunneling from one state to another leads to splitting of the ground level and a decrease in the energetically favorable state by Δ

Rice. 4. Schematic representation of the structure of light nuclei. The dashed line illustrates the possibility of an exchange transition of a relativistic electron between protons

3.2. Deuteron

The electromagnetic model of the neutron, discussed above, allows us to take a fresh look at the mechanism of interaction of the neutron with the proton. Neutron – i.e. a proton surrounded by a relativistic electron cloud and a free proton together form an object similar to a molecular hydrogen ion. The difference is that in this case the electron is relativistic, the radius of its orbit is R 0 ≈ 10–13 cm (28) and mass approximately 2.57 m e.

Application of the results of Heitler–London quantum mechanical calculations to this case makes it possible to estimate the binding energy of the deuteron with an accuracy approximately the same as in the case of the molecular hydrogen ion. The estimate predicts the binding energy to be approximately 2.13 10 –6 erg, while measurements give

3.3. Light kernels

3.3.1. Nucleus 3 2 He

From Fig. 4, which schematically shows the energy bonds in the 3 2 He nucleus, it is clear that they are composed of three pair interactions of protons. Therefore, it should be assumed that the binding energy of this nucleus should be equal to triple the binding energy of the deuteron:

The mass defect of this nucleus

Agreement of assessment E He3 with measured binding energy E(3 2 He) can be considered very good.

3.3.2. Nucleus 4 2 He

From the diagram of energy connections in the 4 2 He nucleus shown in Fig. 4, it is clear that these bonds are formed by six pair interactions of protons, realized by two electrons. For this reason, it can be assumed that the binding energy of the 4 2 He nucleus should be equal to:

The mass defect of this nucleus

This mass defect corresponds to the binding energy

This agreement between these values ​​can be considered quite satisfactory.

3.3.3. Core 6 3 Li

It can be assumed that the binding energy of the Li – 6 nucleus should be close to the sum of the binding energies of the He – 4 nucleus and the deuteron located on the following shell:

This assumption is possible if the exchange of electrons between protons of different shells is difficult.

At the same time, the mass defect of this nucleus

and the associated binding energy

which indeed confirms the weak coupling between protons on different shells.

It should be noted that the situation with other light nuclei is not so simple. Core 3 1 T consists of three protons and two electrons that communicate between them. The jump of two electrons in such a system must obey the Pauli postulate. Apparently, this is the reason that the binding energy of tritium is not very much higher than the binding energy of He – 3.

Nuclear bonds in the 7 3 Li nucleus, it would seem, can be represented by the diagram E Li7 ≈ E He4+ E T, but this idea leads to a rather rough estimate. However, for the unstable nucleus Be – 8 a similar representation E Be8 ≈ 2 E He4 leads to very good agreement with measurements.

3.4. Discussion

The good agreement between the calculated binding energy for some light nuclei and the measurement data suggests that nuclear forces (at least in the case of these nuclei) have the exchange character described above.

For the first time, attention to the possibility of explaining nuclear forces on the basis of the effect of electron exchange was apparently drawn by I.E. Tamm back in the 30s of the last century. However, later in nuclear physics the model of exchange of π-mesons, and then gluons, became dominant. The reason for this is clear. To explain the magnitude and range of nuclear forces, a particle with a short intrinsic wavelength is needed. A nonrelativistic electron is not suitable for this. However, on the other hand, the π-meson or gluon exchange models also did not turn out to be productive. These models were unable to provide a sufficiently accurate quantitative explanation of the binding energy of even light nuclei. Therefore, the above simple and measurement-consistent estimate of this energy is unambiguous evidence that the so-called strong interaction (in the case of some light nuclei) is a manifestation of the effect of attraction between protons arising due to the exchange of a relativistic electron.

4. Neutrinos and mesons

4.1. Neutrino

It was previously shown that within the framework of the standard Maxwellian theory of the electromagnetic field there are two possibilities. Using different excitation methods, it is possible to excite either a transverse electromagnetic wave (photon) or a magnetic quantum (magnetic soliton) in empty space (ether), i.e. a wave devoid of an electrical component. To generate electromagnetic waves in a vacuum, you need to use an oscillating electric or magnetic dipole.

According to Maxwell's equations, the magnitude of the electric field carried by a photon is proportional to the second derivative with respect to time of the time-varying magnetic moment that the photon generates. If the time dependence of the magnetic moment is described by an ideally sharp Heaviside step function, then the first derivative of this step is the δ-function, and the second derivative is zero. Therefore, at the leading edge of the step, which lasts about 10–23 seconds (this is the estimate of the time of transformation of a π-meson into a μ-meson, at which an antineutrino is born), a quantum should be emitted that has a δ-shaped magnetic component and is devoid of an electrical component (see for more details in) .

The characteristic features of a magnetic soliton are that, being circularly polarized, it must have spin ħ  / 2, and its interaction with matter is almost two dozen orders of magnitude weaker than that of an electromagnetic wave. This feature is due to the fact that there are no magnetic monopoles in nature.

This suggests that a magnetic soliton can be identified with a neutrino. In this case, when a magnetic moment is born, an antineutrino appears, and when it disappears, a neutrino appears.

Thus, in the process of sequential transformation of a π  – -meson, first into a μ  – -meson, and then into an electron, three such magnetic γ-quanta appear (Fig. 5).

Rice. 5. Scheme of the birth of three magnetic solitons (neutrinos) during the decay of a π -meson. The π -meson does not have a magnetic moment. During decay, it turns into a μ – -meson, carrying a magnetic moment. This process must be accompanied by the emission of a magnetic γ-quantum (antineutrino emission). When a μ – -meson decays, its magnetic moment disappears and another magnetic γ-quantum (neutrino) is emitted. The third magnetic soliton (antineutrino) appears at the moment of electron birth

4.2. Mesons

In the chain of transformations pion → muon → electron, three neutrinos are born (Fig. 5). Charged pions (π -mesons), whose spins are zero, do not have magnetic dipoles. At the moment of transformation of the π  – meson into a muon (μ‑meson), a magnetic moment appears abruptly, which is accompanied by the emission of a muon antineutrino \((\widetilde \nu _\mu )\). When a muon decays, muon neutrino radiation ν μ is generated, which is caused by the disappearance of the muon magnetic moment. At the same time, an electron with a magnetic moment is born, which leads to the emission of an electron antineutrino \(\mathop (\widetilde \nu )\nolimits_e \).

The fact that no other products besides neutrinos and antineutrinos arise in these reactions leads us to the assumption that the pion and muon are not independent elementary particles, but are excited states of the electron.

These mesons have masses

here λ D= 2π ħ  / P– de Broglie wavelength,

P– generalized particle momentum,

n= 1, 2, 3... – integer.

The invariant angular momentum (spin) of such a particle

we get

This mass value is very close to the mass of the π meson (46), which has a spin equal to zero:

This mass value is very close to the mass of the μ-meson (46), which has a spin equal to ħ  / 2:

\[\frac(((M_(1/2))))(((M_((\mu ^ \pm ))))) \simeq 0.9941.\]

(54)

The discovered possibility of calculating the masses of mesons based only on their spins confirms the assumption that these mesons are excited states of the electron.

5. Conclusion

The above calculations of the properties of elementary particles reveal the insufficiency of the quark model with fractional charges of quarks, within which such estimates cannot be obtained. This model in its modern form demonstrates the possibility of classifying particles, but this does not prove that such a classification is the only possible and correct one.

It is important to note that to describe the proton-neutron interaction (in light nuclei) there is no need to involve the gluon model, nor to use the theories of strong and weak interactions.

Indeed, the exchange of a relativistic electron between protons in a deuteron and as well as the exchange of a non-relativistic electron in a molecular hydrogen ion is a quantum mechanical phenomenon and there is no reason to attribute to this exchange effect in the case of a deuteron the role of a fundamental interaction of Nature.

Neutrino emission occurs during the process of β-decay (or K-capture). The decay processes of nuclei, both α and β, do not require the introduction of any new special fundamental natural interaction. But β-decay has an essential feature: during β-decay, a magnetic moment of a free electron appears (or disappears during K-capture) in an extremely short time. This produces a magnetic impact on the ether and leads to the emission of a magnetic γ-quantum, i.e. neutrino. This phenomenon is purely electromagnetic in nature, and to describe it there is no need to introduce a special weak or electroweak interaction.

However, the absence of the need to introduce strong and weak interactions into the description of other objects of the microworld has not been formally proven. It is obvious that to calculate nuclear forces in heavy nuclei it will be necessary to involve other effects associated, for example, with the existence of nuclear shells.

Nevertheless, the possibility of an electromagnetic description of some particles makes relevant the question of the correctness of the existing description of many other, more complex objects of the microworld.

Obviously, in accordance with the main postulate of the natural sciences of W. Gilbert, verification of the correctness of such a description should be based on experimental data on the basic properties of the objects under study. A successful method of systematizing particles into a certain table cannot be considered an exhaustive proof of the correctness and uniqueness of this approach.

Literature:

1. Gilbert W. About the magnet, magnetic bodies and the big magnet - the Earth. M.: Publishing House of the USSR Academy of Sciences, 1956.
, 2016.

Systematics of elementary particles. Superelementary particles. The main difficulty that arises in defining the concept of an elementary particle is due to the fact that at present there are many more such particles than there are atoms of chemical elements.

Particles 10 times heavier than a proton and with approximately the same mass as a boron nucleus have recently been discovered. Desperate to identify any hierarchy in the growing set of equally elementary objects, some physicists have put forward the idea of ​​bootstrap lacing, or nuclear democracy, according to which each elementary particle consists of all other particles, or rather, the structure of each elementary particle is determined by the interactions of all other particles.

However, this idea does not eliminate the feeling of satisfaction due to too many simplest entities; a consistent formulation of the bootstrap idea, somewhat reminiscent of the concept of Democritus, leads to the conclusion about an infinite number of elementary objects. The structure of micro-objects in bootstrap theory takes on a relative meaning, something like a special coordinate system that can be chosen in different ways. The definition of structure elements becomes very ambiguous.

Since one and the same particle can be composed of other particles in different ways. Moreover, it remains unclear whether it is even possible in this way to formulate an exact closed system of equations that determines various properties, including the structure of elementary particles. Theorists have analyzed only very rough bootstrap models that take into account the relationship of only two or three types of particles, and although in a number of cases encouraging qualitative results have been obtained, attempts to refine them immediately encounter enormous difficulties.

The bootstrap idea cannot be considered a satisfactory solution to the problem of the simplest elements. The way of combining particles into closed groups of multiplets, the members of each of which can be interpreted as different states of the same particle, turned out to be much more fruitful. The guiding principle here is to identify symmetries in the properties of various particles.

This group approach, using the well-developed mathematical apparatus of group theory, is a further development of the formalism of charge isotopic multiplets. Of great importance was the discovery of the so-called unitary symmetry, which made it possible to combine the isotopic multiplets of ordinary and strange particles into single octets and decaplets. Taking spins into account made it possible to construct even more complex families of particles: unitary multiplets of mesons united into a family consisting of 35 particles 35 - plet, and the octet and decaplet of baryons into a family of 56 elements 56 - plet. Further development of particle taxonomy is associated with the idea of ​​quarks.

It turned out that individual unitary multiplets are not completely isolated from each other, but are connected by strict symmetry rules. And the most amazing thing was that these rules predicted the existence of particles with fractional electric charges of quarks. These particles, at the modern level of development of science, can really be considered the most elementary, because from them all other interacting particles can be built, sometimes by simple addition, like atomic nuclei from protons and neutrons, and sometimes by considering them as excited states of already constructed particles and in At the same time, quarks themselves cannot be built from other elementary particles. In this sense, quarks differ significantly from all other particles, among which, as already noted, it is impossible to identify any more elementary building elements.

Quarks can be considered as the next, deeper, superelementary level of organization of matter and from the point of view of the magnitude of the mass defect, that is, the density from the packing inside protons, mesons and other less elementary objects.

From the perspective of quark theory, the structural level of elementary particles is the region of objects consisting of quarks and antiquarks and characterized by a large mass defect in relation to any of their decays and virtual dissociations.

At the same time, although the quark is the simplest particle known today, it has very complex properties. A quark differs from all other particles known to us not only in its fractional electric charge, but also in its fractional baryon number. Among other elementary particles, it looks like a kind of centaur; in its properties, it is both a meson and a baryon. It was initially believed that a quark has three states, two of which differ only in the magnitude of the electric charge, and in the third state the quark appears as a strange particle.

However, after the discovery of families of charmed charmed particles, a fourth charm had to be added to the three states of the quark. At the world's largest proton accelerator in Batavia, near Chicago, a new amazing particle was discovered - the meson. Its mass significantly exceeds the mass of a nucleon, and its properties are such that it has to be considered as a quark and an antiquark stuck together. In this case, we have to assume that the quark and antiquark have one more, fifth state.

The quantum number characterizing this state does not yet have even a generally accepted name; most often it is called the beauty of a quark or the corresponding English term beauty. The five quantum degrees of freedom of a quark are usually called its flavor; some authors prefer to talk about the five degrees of taste of a quark. But these do not exhaust the list of quark properties. Analysis of experimental data led to the conclusion that each of the five quark flavors has three colors, that is, each of the five quark states is split into three more independent states, characterized by the value of a specific color quantum number.

The color of a quark changes when it emits or absorbs a gluon, a quantum of the intermediate field that glues quarks and antiquarks into mesons and baryons. We can say that the gluon field is a field of color, its quanta transfer color. The term gluons comes from the English word glue. Currently, the idea of ​​superelementary quark particles literally permeates energy physics.

With their help, so much experimental data is explained that it is simply impossible for a physicist to do without these amazing particles, just as, for example, a chemist cannot do without atoms and molecules. According to most physicists, if quarks do not exist in nature as real objects, then this in itself would be a stunning mystery. And at the same time, quarks have never been observed in their pure form, although almost two decades have passed since they were introduced into the theory.

All numerous attempts to detect quarks or gluons in a free state invariably end in failure. Strictly speaking, gluons and quarks still remain, although probable, but still hypothetical objects. Indirect experiments convince us that quarks and gluons are physical objects, and not just a convenient phenomenological way of describing in the corpuscular language familiar to us some other incomprehensible aspects of the structure of elementary particles. First of all, these are experiments on probing protons into neutrons using very fast electrons and neutrinos, when the incident particle scatters and rebounds, colliding with one of the quarks located inside the target particle. Taking quarks into account, the list of strongly interacting superelementary particles will be reduced to three particles: a quark, an antiquark, and the gluon that binds them.

To these should be added about a dozen of the simplest particles of other types, the structure of which has not yet manifested itself in experiment: the quantum of the electromagnetic field, the photon, confidently predicted by theorists, the graviton and the family of leptons.

Conclusion. Over the past years, the situation in the theory of elementary particles has changed significantly. Weak neutral currents were discovered, leading to effects such as the scattering of muon neutrinos by electrons. A whole group of elementary particles with a lifetime that is a thousand times longer than the lifetime of resonances has been discovered, starting with the J-meson. In fact, now it is necessary to include these particles in the table of relatively stable elementary particles.

Significant advances have been made in the theory of elementary particles. The unified theory of weak and electromagnetic interactions has received solid experimental confirmation, although it still cannot be considered absolutely reliable. The quark model of the structure of hadrons is receiving more and more experimental confirmation. After many years of stagnation, great progress has been made in the theory of strong interactions, which are now considered to be interquark interactions.

It is very likely that the truly elementary particles, no longer indivisible, are leptons and quarks. The vast majority of hadrons are built from quarks. The model of four colored quarks and four leptons allows us to understand in general terms the structure of matter. Scientists have come close to solving a new problem, the problem of the structure of elementary particles. When bombarding a stationary target with high-energy protons, superheavy neutral mesons, called upsilons, with a mass of about 9.4 GeV were discovered. Three modifications of these mesons with similar masses have been found.

To include upsilons in the framework of the quark model, one must assume that there are quarks more massive than the c-quark. To preserve quark-lepton symmetry, the introduction of two new quarks, corresponding to the -lepton, -neutrino pair, is required. These quarks have already received the name top top in English and bottom bottom. So, with an increase in the energy of colliding particles, the birth of new, heavier and heavier particles is detected.

This complicates the already complex picture of the world of elementary particles. New problems are emerging, although many old problems remain unresolved. Probably, the main unresolved problem should be considered the problem of quarks: can they be free or is their capture inside hadrons absolute? If quarks cannot in principle be isolated and detected in a free state, then how can one be convinced that they undoubtedly exist? Further, the existence of intermediate vector bosons W, W- and W0, which are so necessary for confidence in the validity of a unified theory of weak and electromagnetic interactions, will remain unproved experimentally .

There is no doubt that elucidation of the structure of elementary particles will be as significant a step as the discovery of the structure of the atom and nucleus.

End of work -

This topic belongs to the section:

The formation of the physical picture of the world from Galileo to Einstein

The functional significance of this kind of summary knowledge is seen in ensuring the synthesis of knowledge, the connection of various branches of natural science. At the same time, there are discrepancies in the understanding of why synthesis is necessary. This difference in the understanding of the functions of the picture of the world, in turn, leads to a discrepancy in the very approach to its analysis. In the first place..

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Introduction

1. The origin and development of ideas about quantum

1.1 Bohr's theory of the atom

2. Elementary particles and the problem of their structure

Conclusion

Bibliography

Introduction

In the study of nature, two stages can be distinguished: pre-scientific and scientific stages. The pre-scientific or natural-philosophical stage covers the period from the ancient period to the establishment of experimental natural science in the 16th-17th centuries. Ideas about nature during this period were of a purely natural-philosophical nature; observed natural phenomena were explained on the basis of mentally assembled philosophical principles. The greatest achievement of natural science during this period was the doctrine of ancient atomism, which was considered a discrete concept of the structure of matter. According to this doctrine, all bodies are formed from atoms, considered the smallest particles of matter. According to ancient atomism, which provided the primary theoretical model of the atom, atoms are invisible, indivisible and impenetrable microparticles, differing from each other only in quantitative relationships - shape, size, structure. Ancient atomism, which explained the whole as a mechanical set of parts that form it, was the first theoretical program. According to the teachings of Democritus, a vacuum is necessary to explain the mechanical placement of bodies in space and their deformation (compression, elongation, etc.) under the influence of external forces. Atomism explained the essence of natural processes by the mechanical interaction of atoms, their attraction and repulsion. The mechanical program for explaining nature, first put forward in ancient atomism, was realized in classical mechanics, which laid the foundation for the study of nature in a scientific way. Modern scientific ideas about the structural levels of the formation of matter should begin with the concept of classical physics about the study of the microworld, which arose as a result of a critical study of the concepts of classical mechanics, which are applied only in the microworld. The formation of scientific ideas about the structure of matter dates back to the 16th century, to the period when G. Galileo laid the foundations of the mechanical picture of the world. Galileo not only substantiated the heliocentric system of N. Copernicus, discovered the laws of inertia of motion and free fall, he also developed a new methodological way of describing nature - the scientific-theoretical method. The essence of this method lies in the fact that, having selected a number of physical and geometric characteristics of nature, Galileo turned them into the subject of scientific research. The selection of individual characteristics of an object provided the opportunity to create theoretical models and test them based on scientific experiment. The methodological concept formulated by Galileo played a decisive role in the establishment of classical natural science.

1. Origin anddevelopment of ideas about quantum

quantum elementary particle

During the transition of physics from the study of the macroworld to the study of the microworld, the ideas of classical physics about matter and field radically changed. While studying microparticles, scientists came across a picture that seemed paradoxical from the point of view of classical physics: the same object demonstrates both the property of waviness and the property of corpuscularity. This phenomenon is called wave-particle duality.

The first step in the field of studying the contradictory nature of particles was made by the German scientist Max Planck. It all started with the appearance in physics at the end of the 19th century of such a problem as the “ultraviolet catastrophe.” According to calculations based on the formulas of classical electrodynamics, the intensity of radiation from dark objects alone increased indefinitely. This was contrary to practice. From research conducted on the radiation of heat, M. Planck came to the conclusion that in the process of radiation, energy is emitted not in an arbitrary quantity and infinitely, but in indivisible portions - quanta. The quantum energy is determined by the number of oscillations corresponding to radiation (V) and the universal constant called Planck's constant: E=hn. As Planck noted, the arrival of the idea of ​​quantum in physics cannot yet be associated with the creation of quantum theory, however, December 14, 1900, the date of the appearance of the formula for quantum energy, became the date of laying the foundation of the same theory, the day of the birth of atomic physics and the beginning of a new period in natural science.

The first physicist who greeted the discovery of the influence of the elementary quantum with high spiritual inspiration and developed it in creativity. There was A. Einstein. In 1905, applying the idea of ​​the quantitative nature of radiation and absorption of energy during thermal radiation to radiation phenomena in general, he laid the foundation for quantum theory. Einstein, applying Planck's hypothesis to light phenomena, came to the conclusion that it was necessary to accept the corpuscular structure of light. The quantum theory of light or Einstein's theory of the photon confirmed that along with the fact that light is a wave phenomenon of propagation in space, it also has a continuous structure. Light can be considered as indivisible energy portions, light quanta and photons. The energy of photons is determined by Planck's constant (h) and the speed of the corresponding oscillations (n). Monochromatic light of various colors (red, yellow, green, blue, violet and others) consists of light quanta of different energies. Einstein's idea of ​​light quanta provided an opportunity to understand and visually describe the photoelectric phenomenon, the essence of which is the separation of an electron from light matter. Experiments have shown that the existence of the photoelectric effect is determined not by the intensity of the light wave incident on the metal, but by the frequency of the light. If we assume that each photoelectron is separated by one photon, it becomes clear that the effect occurs when the energy of the photon becomes large enough to break the mutual connection of matter and electron.

10 years after the origin of the interpretation of the photoelectric effect in a similar situation, it was confirmed by the experiments of the American physicist R.E. Milliken. Discovered in 1923 by the American scientist A.H. Compton's phenomenon (“Compton effect”) finally confirmed the quantum theory. In general, the quantum theory of light is one of the theories of physics that has been repeatedly confirmed by experiments. However, in this way the wave nature of light was finally confirmed by experiments on the phenomena of diffraction interference. In this regard, such a paradoxical situation was created: it became known that light behaves both as a wave and as a corpuscular at the same time. In this case, the photon acts as a specific type of corpuscular. The main characteristic of the discreteness of a photon, a special portion of energy (E=hn) is determined by the characteristic of a pure wave - frequency (n). Like all great natural scientific discoveries, the quantum theory of light has acquired a significant ideological, theoretical and cognitive character.

The idea of ​​phonons-quanta of the electromagnetic field became a great gift to the development of quantum theory. Therefore, A. Einstein is considered one of the great creators of quantum theory. Einstein's theory, developing the views of M. Planck, provided the opportunity for the Danish scientist N. Bohr to develop a new model of the atom.

1.1 Ttheory of the atom proposed by Bohr

In 1913, the Danish scientist Niels Bohr, applying the principle of quantity to solving problems of the structure of the atom and the characteristics of the spectrum of the atom, eliminated the contradictions in the model of the atom created by Rutherford. The model of the atom proposed in 1911 by Rutherford resembled the solar system: the nucleus was located in the center, and electrons revolved around it in circular orbits. The nucleus was positively charged, the electrons had a negative electrical charge. The forces of attraction in the solar system in the atom were replaced by electrical forces. The positive electric charge of the atomic nucleus, which was equal to the atomic number of the element in Mendeleev's periodic system, was balanced by the negative electric charge of the electrons. Therefore, the atom was electrically neutral.

The analysis of the planetary model of the atom within the framework of classical electrodynamics contained two impossible contradictions. The first of these contradictions was that electrons, in order not to lose their stability, must rotate around the nucleus. As is known, circular motion is characterized by centrifugal acceleration. According to the laws of classical electrodynamics, accelerated electrons must certainly emit electromagnetic energy. However, in this case, electrons must fall onto the nucleus in a very short period (10-8 seconds), spending their energy on radiation. We know this well from everyday experience. If electrons fell onto the nucleus, a body consisting of them, for example the table in front of us, would change its size by 10 thousand times.

The second contradiction of the planetary model of the atom is related to the fact that the electron, gradually approaching the nucleus as a result of radiation, for the continuous change of its frequency, the radiation spectrum of the atom must be intact. Experience shows that the emission spectrum of an atom is linear. In other words, Rutherford's planetary model of the atom does not coexist with Maxwell's electrodynamics.

The quantum theory of the atom, which could solve both of these contradictions (the so-called “Bohr’s theory of the structure of the atom”) was put forward by N. Bohr. The content of this theory was formed from the following provisions, combined into a single, whole idea:

regularities of the linear spectrum of the hydrogen atom;

nuclear model of the atom proposed by Rutherford;

quantum nature of radiation and absorption of light.

The new hypothesis put forward by N. Bohr to explain the structure of the atom was based on three postulates that did not harmonize with the principles of classical physics.

The first postulate: in each atom there are several stationary states of electrons (stationary orbits). Electromagnetic waves moving along the stationary orbits of an atom are neither emitted nor absorbed.

The second postulate: an atom only emits or absorbs a portion of energy when an electron passes from one stationary state to another.

Third postulate? The electron moves around the nucleus in such circular stationary orbits in which, at the moment of electron momentum, Planck’s constant is completely similar to the relative 2p:

where m, n, r are respectively the mass of the electron, the speed and radius of the stationary orbit in which it moves, n=1,2,3... are integers.

These postulates laid the foundation for a new period in the study of the properties and structure of the atom.

The first postulate showed the limitations of classical physics, and in special cases the inappropriateness of its laws to stationary states. It is not so easy to accept the idea of ​​electrons emitting energy in specifically selected orbits. At this very moment the question arises: “Why?” However, due to the fact that this postulate was adequate to the experimental results, physicists were forced to accept it. From the second postulate the conclusion follows that the energy of an atom is emitted in portions. The transition of an electron from one orbit to another is necessarily accompanied by integer numbers of energy quanta. Thus, the state of electrons in an atom is characterized by 4 quantum numbers - the main, orbital, magnetic and orbital quantum numbers. The main quantum number (n) determines the energy of the electron in the regions of the nucleus; in complex atoms, the serial number of the layer of electrons. The orbital quantum number (l) characterizes the adjustments introduced into the energy of an atom by the simultaneous movement of atoms. The spin quantum number (s) determines the special mechanical torque characterizing the rotational motion of electrons. Bohr's postulates explained the stability of the atom: in stationary states, an electron does not emit electromagnetic energy without the existence of external causes. Only now has it become clear why, with a constant assessment of states, atoms of chemical elements do not emit electromagnetic waves. The atomic model proposed by Bohr, despite the fact that it gave an accurate description of the hydrogen atom, consisting of one proton and one electron, and this description agreed quite well with the experimental facts, the later application of this model to multi-electron atoms encountered certain difficulties. No matter how accurately theorists tried to describe the movement and orbit of electrons in an atom, the difference between theoretical results and experimental data remained large. However, during the development of quantum theory, it became clear that these differences are mainly associated with the waviness property of electrons. The wavelength of an electron moving in a circular orbit in an atom was part of the measurements of the atom and was approximately 10-8 cm. Although the movement of particles inherent in any system can only be described quite accurately as the mechanical movement of a material point in a closed orbit , when the wavelength of the particle compared to the system of changes will be so small that it will not be taken into account. In other words, you need to take into account that an electron is not a point, not a strong “ball”; it has an internal structure that can change depending on its inherent states. However, in this case, the details of the internal structure of the electron remain unknown. Here it becomes clear that it is fundamentally impossible to imagine the structure of an atom on the basis of ideas about the orbits of supposedly point electrons, therefore the internal orbits of an atom have become ideal objects; they do not even exist in reality. According to their wave nature, electrons and their electric charge are supposedly unevenly distributed throughout the atom and have a low electron density at some points and a higher electron density at others. A description of the distribution of electron charge density inside an atom is given in quantum mechanics: at some points the electron charge density reaches its maximum. The curve connecting the points of maximum marks of the electron charge density is formally called the electron orbit. The trajectory of the hydrogen atom calculated in Bohr's theory coincided with the curve passing through the points of maximum marks of the average charge density, which in turn fully corresponds to the experimental data. Bohr's theory seems to outline the boundary line of the first stage in the development of modern physics. Bohr's atomic theory, by adding a small number of new considerations, was the last attempt to describe the structure of the atom on the basis of classical physics. Bohr's postulates showed that classical physics is not able to explain such results from the simplest experiments related to the structure of the atom. Bohr's postulates, alien to classical physics, violated its integrity and, in turn, were able to explain only a small area of ​​experimental data. Therefore, the idea arises that Bohr’s postulates, which discovered new, hitherto unknown to science, properties of matter, at the same time partially and did not fully reflect them. Bohr's theory, and his postulates which could not be applied to complex atoms, were powerless in explaining the essential phenomena of physics, just as diffraction and interference could not explain the wave properties of light and matter. Many questions related to the structure of the atom were answered only as a result of the development of quantum mechanics. It was found that Bohr's model of the atom cannot be literally understood as it was before. It would be incorrect to visually describe the processes of the atom in the forms of mechanical models created by analogy with the phenomena of the macrocosm. It soon became known that the concepts of time and space precisely defined for the macrocosm are unsuitable for describing microphysical phenomena. Gradually, theoretical physicists turned the atom into an even more abstract system - a set of unobservable equations.

2. Elementary partsobjects and the problem of their structure

The problem of the structure of matter has been one of the pressing problems that has always been at the center of attention of natural science, especially in its advanced field - physics. Clearly reflecting the relationship between philosophy and natural science, this problem has not only philosophical, but also practical and industrial-technical significance. To do this, it is enough to say that modern physical theories, which form an important stage in the scientific and technological revolution, including quantum mechanics and the theory of elementary particles, are closely related to the discovery and use of nuclear energy, which laid the foundation for the “atomic age.”

Modern physics has achieved great achievements in the field of studying the structure and properties of matter. However, despite this, nature has many still undiscovered secrets in the field of the structure and properties of matter. Penetrating into the depths of theoretical cognitive matter and discovering new levels of its structure, we believe this more and more. At the present stage of its development, physics has entered a path full of scientific discoveries that leads it forward in the direction of even greater mastery of the forces of human nature. However, physics did not immediately take this path. Before achieving certain achievements along this path, it went through a long and difficult path of development, and during this period it eliminated natural philosophical metaphysical ideas about the structure and properties of matter inherent in one of the eras.

The modern doctrine of the structure of matter began to emerge on the basis of stable practical facts, starting only at the end of the 19th and beginning of the 20th centuries. Without stopping at the successes of scientific knowledge, this teaching, which was enriched and developed, united four aspects organically connected with each other: first of all, this teaching is an atomistic teaching, because according to this teaching, every body, every physical area is formed from microparticles and microregions , secondly, this doctrine is a statistical doctrine, because, based on statistical concepts, it determines the properties and patterns of movement of micro-objects, their mutual influences and transformations by statistical laws, thirdly, this doctrine is quantum theory, and the properties and patterns of movement of microparticles are qualitatively different from the properties and patterns of movement of microscopic bodies determined by classical physics; finally, this teaching is a relativistic teaching, because in this theory the connection between space, time and matter is described through a relativistic theory - the theory of relativity.

Developing human knowledge, not stopping at the field of knowledge of the structure and properties of matter, discovered its complexity of structure and inexhaustibility of properties and confirmed this with new facts. The greatest achievement achieved in the field of studying the structure of matter is the transition from the atomic level to the level of elementary particles. The first elementary particle discovered at the end of the 19th century was the electron; in the first half of the 20th century, the photon, proton, positron, neutron, neutrino and other elementary particles were discovered. Currently, elementary particles are considered the smallest “elementary” particles among micro-objects surrounding atoms and molecules. After the Second World War, thanks to the use of modern experimental technology and, first of all, powerful accelerators that create conditions of high energy and enormous speeds, the existence of more than 300 elementary particles was discovered. One part of the elementary particles was discovered in experiment, the other part (resonances, quarks, virtual particles) were considered theoretical.

What does the concept of “elementary particle” express in modern physics? Before answering this question, it is necessary to note the inherent aspect of the natural scientific concept that, like all physical concepts, the concept of “elementary” is relative and acquires different meanings at different stages of the development of scientific knowledge. Until the mid-60s of our century, ideas about elementary particles resembled one of the types of views on atoms expressed by Democritus. However, these first naive ideas about elementary particles did not last long: it was soon proven that there are no unchanging, impenetrable, structureless particles. Under the influence of real facts, the concept of “elementary” has undergone changes and, in general, everything that can be called an “elementary particle” has taken on an indefinite character. Currently, a number of authors rightly note that the concept of “elementary” is used in two meanings: on the one hand, as a synonym for the simplest, on the other hand, as a subatomic particle, that is, an indicator of fundamentality. Taking into account each two meanings expressed by the concept of “elementary particle”, we can say in the full and broad sense of the word that the so-called “elementary” particles are such material formations that consist of other particles known to science and are found as a single whole in all processes in mutual influence, which include the physical quantities that characterize them - mass, electron charge, spin, pairing, singleness, isotropic spin and other initial parameters that cannot be theoretically calculated and can be accurately applied to physical theory only experimentally.

Physics of elementary particles is, in the words of the scientist academician I.B. Tammin, the main field “leading modern physics to the eve of significant changes and revolutionary upheavals.” Elementary particles were figuratively likened to “unexplored planets.” It is no coincidence that noteworthy discoveries in physics were made after the 60s in this area. In order to get an idea of ​​the achievements in this area, it is enough to say that over the past 25-30 years the number of elementary particles has increased from 35 to 340 and a further increase in this figure is expected in the future. Especially since the 30s of our century, in addition to the previously known electron, photon and proton, many additional new particles were discovered: neutron, positron, neutrons of various masses and charges (also neutral), mesons, hyperons and their so-called corresponding antiparticles. The increase in the number expressing the number of “elementary” particles showed the loss of its former meaning of the concept of “elementary”. Because all these particles could not fulfill the function of the last “bricks” in the world building. Being in this position, elementary particles tried to explain the multitude and diversity, to classify from the point of view of ensuring development, to classify from the point of view of ensuring the development of achievements of scientific knowledge in this area. The implementation of such classifications is associated with a description of the properties and main characteristics of elementary particles.

Currently, a wealth of properties of elementary particles known in science has been determined. Moreover, many of these properties have no analogues among the known properties of macroscopic objects. The main characteristics of elementary particles described in the abstract language of mathematics are the following: mass, charge, average period of existence, spin, isotropic spin, singleness, pairing, leptin charge, borion charge, mutual influence. We will try to characterize this property of elementary particles.

One of the most important properties characterizing elementary particles is mass. Note that the rest mass of elementary particles is determined relative to the rest mass of the electron (me=9.1×10-31 kg). Currently, the classification of elementary particles depending on the value of their rest mass is more widespread. According to this classification, all elementary particles are divided into 4 groups: 1) light elementary particles - leptons. This includes the electron, neutrino and their antiparticles - positron, antineutrino, as well as positive and negative mu-mesons. With the exception of the latter, leptons are stable before entering into mutual influence and exist in a free state for more than 1020 years. Mu-mesons are not stable particles; after living for two hundred millionths of a second, they decay and turn into an electron, neutron and antineutron. The rest mass of neutrinos and antineutrinos is very small; taken together they are equal to 0.0005 of the mass of an electron.

2) particles of average mass - mesons. This includes positive, negative and neutral pi mesons with a mass of 270 me - rest mass, and some types of ka-mesons with a mass of 970 me. All mesons are unstable and have a very short period of existence (up to 7-19 seconds).

3) heavy particles - nucleons. This includes the proton, neutron and their antiparticles - antiproton and antineutron. The proton and antiproton are stable, the neutron and antineutron are unstable particles and have a relatively long lifetime - 17 minutes.

4) hyperons are the heaviest particles. This group includes a lot of particles and antiparticles. The mass of hyperons is from 2182 me to 2585 me. The lifetime of all hyperons is the same - 10-10 seconds.

Sometimes nucleons and hyperons are combined into a single group called baryons. This group can also include the photon, which forms a special group and is a quantum of the electromagnetic field. Despite the fact that such a classification of elementary particles does not reveal the basic laws that unite them, in any case, it provides the opportunity to study a number of properties and transformations of particles and even predict the existence of some particles. It should be noted that the structure of matter and the inexhaustibility of properties find themselves not only in the gradual increase in the number of known particles, but also in the less important fact of the mutual transformation of particles of “elementary” matter. The definition of generality (dualism) in the properties of field matter particles also led to the idea of ​​their mutual transformation. Already some time after the discovery of the positron (1932), it became known that electron-positron matter pairs, when combined under certain conditions, turn into light quanta - photons, which are particles of the electromagnetic field, and are formed from them. Then it became known that such a mutual transformation occurs not only between particles of matter and field, which are two types of matter, but also between the particles of matter themselves. As a result, it became clear that particles of matter are not immutable and simple; they can transform into each other in the process of mutual influence, and can be formed and absorbed by various particle complexes. Another important property of elementary particles is their electric charge, which reflects their connection with the electromagnetic field. One part of the known particles has a positive charge, the other part has a negative charge, and some particles have no electric charge. In addition to the photon and both mesons, each particle has an antiparticle of opposite charge. The reason that different elementary particles do not necessarily have the same electric charge and that some elementary particles lack electric charge is not yet known to us. It is very possible that this is a manifestation of the yet undiscovered deep internal patterns of elementary particles of commonality in the structure of particles. One of the essential physical characteristics of elementary particles is the period of their existence. According to the period of existence, elementary particles are divided into stable, quasi-stable and unstable (resonant) particles. There are five stable particles: photon, electron neutrono, mion neutrono, electron and proton. In the structure of macrobodies, stable particles play a decisive role. The remaining particles are not stable. These particles, which range from an average lifetime of 10-10 to 10-24 seconds, eventually split into other particles. Quasistable elementary particles with average periods of existence from 10-10 to 10-24 seconds are called resonances. Due to their short period of existence, these particles cannot leave the atom or the nucleus of an atom and disintegrate into other particles. The existence of resonant particles was only theoretically calculated and it is not yet possible to notice them in a real experiment.

Another important characteristic of particles is spin. Spin is a completely new property of particles that is inherent only to them and has no analogue in macroscopic physics; its description as a moment of mechanical momentum is in itself crude and inaccurate. We can look at spin as a special “rotation”, analogous to the rotation of a particle in the macrocosm. The spin of elementary particles is measured in units and can neither be increased nor decreased. Spin determines the general nature of the type of statistics included in the particle (Bose-Einstein and Fermi-Dirac statistics) and the theory that describes its motion. The spin of a proton, neutron and electron is S-e, the spin of a photon is 1-e. Particles with half spin obey Fermi-Dirac statistics and are called fermions, particles with full spin obey Bose-Einstein statistics and are called bosons. It is known that in the same situation, when suddenly a fermion is no longer possible, there can be several bosons in the same situation. Thus, fermions behave as “individualists”, bosons - as “collectivists”. Despite the fact that this property of the internal nature of elementary particles has not yet been fully studied, the connection of these properties with the properties of symmetry and asymmetry of space has now been determined. Spin is considered as a manifestation of the degree of internal independence in the movement of elementary particles. Thus, each elementary particle is characterized by 4 degrees of independence: three of them are degrees of external freedom, expressing the movement of the particle in space; one is the internal degree of freedom of the spin. The existence of spin also indicates the complex structure of the particle and a certain type of internal connections. One of the important properties of elementary particles is also the magnetic moment. This property occurs in both charged and uncharged particles. It is assumed that a certain part of the magnetic moment of charged particles is determined by their location in space. For example, it is assumed that the magnetic moment of protons and neutrons is due to the current created by clouds of mesons gathered around them. Let's take a broader look at this problem. It is known that despite the fact that a neutron has no electric charge, it has a certain amount of magnetic moment. This shows that the magnetic moment of a particle should not be primarily determined by its internal structure. In this case, how should the creation of the neutron magnetic moment be explained? It is assumed that due to the fact that the neutron is an unstable particle, it dissociates into a proton and into a positive meson quantum of the meson field, and approximately 25% of its existence is in this position. Therefore, the neutron acquires 25% of the magnetic moment of the positive pimeson. The experimentally observed magnetic moment of the neutron is very close to the number calculated theoretically. Elementary particles, in addition to the electric charge, are additionally characterized by the charges of the lepton and baryon. The Lepton charge of all leptons is taken as +1, the baryon charge of all baryons is taken as +1. Pairing is also one of the important characteristics of elementary particles. This value applies to right and left symmetries. In the theory of elementary particles, the coordinates of each particle are characterized by a wave function y, which may or may not change the mark of these coordinates as a mirror image (x® -x, u® -u, z® -z). In the first case, the function y is asymmetric or a single function, the pairing of the corresponding particle is +1, in the second case, the function y is symmetric or paired, but the pairing of the particle is taken to be -1. One of the very important characteristics of elementary particles is also mutual transformation, accompanied by the emission and absorption of quanta of the field corresponding to the elementary particles during the period of mutual influence. These processes, which differ from each other in the intensity of their occurrence, determine the division of the mutual influence inherent in elementary particles into 4 types: strong, electromagnetic, weak and gravitational mutual influence. The properties of elementary particles are mainly determined by strong electromagnetic and weak mutual influences. Strong mutual influences occur at the level of the atomic nucleus, their constituent parts consisting of mutual attraction and repulsion. The forces of mutual influence, called nuclear forces, extend over a very small distance - 10-13 cm. Strong mutual influences, firmly binding protons and neutrons under certain conditions, create a material system characterized by high binding energy - the nucleus of an atom. Despite the fact that electromagnetic mutual influences are approximately 1000 times weaker than strong mutual influences, the radius of their influence is close to infinity. This type of mutual influence is characteristic of electrically charged particles. The carrier of electromagnetic mutual influence is free from electric charge and rest mass of the photon. A photon is a quantum of the electromagnetic field. Through electromagnetic mutual influences, combining the nucleus of an atom and an electron into a single system, atoms are created, and by combining, atoms create molecules. Electromagnetic mutual influences are the main mutual influences accompanied by chemical and biological processes.

Weak mutual influences exist between different particles. Weak mutual influences associated with the process of spontaneous decay of particles, for example, with the process of transformation of a neutron in a nucleus into a proton, electron and antineutrino (n0® p+ + e- +n), can extend over a very small distance (10-15 - 10-22 cm). According to modern scientific knowledge, most particles are unstable only due to weak mutual influences. Gravitational mutual influences are extremely weak forces that are taken into account in the theory of elementary particles. For comparison, we note that they are 1040 times weaker than strong mutually influencing forces. However, for ultra-small distances (on the order of 10-33 cm) and ultra-high energies, gravitational forces become significant; in terms of their strength, they acquire a worthy form for comparison with other types of mutual influence. On a cosmic scale, gravitational mutual influences play a decisive role. The radius of influence of these forces is unlimited. In nature, not one, but sometimes several types of mutual influence and properties act between elementary particles, and the structure of particles is determined by the commonality of all types of mutual influence taking part. For example, the proton, which is part of the hadronic type of elementary particles, takes part in strong mutual influence, and in electromagnetic mutual influence due to the fact that it is an electrically charged particle. On the other hand, a proton can be generated in the b decay process of a neutron, that is, in weak mutual influences, thus it is associated with weak mutual influences. And finally, the proton, as a material formation with mass, takes part in gravitational mutual influences. Unlike the proton, a number of elementary particles take part in all types of mutual influence, but only in some of their types. For example, a neutron, due to the fact that it is an uncharged particle, does not take part in electromagnetic mutual influences, and the electron and mu-mesons do not participate in strong mutual influences. Fundamental mutual influences are the reason for the transformation of particles - their destruction and generation. For example, the collision of a neutron and a proton produces two neutrons and one positive pimeson. The period of transformation of elementary particles depends on the mutually influencing force. Nuclear reactions associated with strong mutual influences occur in 10-24 - 10-23 seconds. This is the period when an elementary particle transforms into a high-energy particle and acquires a speed close to the speed of light, dimensions of the order of 10-13 cm. Changes caused by electromagnetic mutual influences occur in 10-21 - 10-19 seconds, changes caused by weak mutual influences (for example, the process of decay of elementary particles) - in 10-10 seconds. The period of various changes occurring in the microcosm can be approached from the point of view of reasoning about the creating mutual influences. Quanta of mutual influence of elementary particles are realized through the physical fields corresponding to these particles. In modern quantum theory, a field is understood as a system of particles that change in number (sex quanta). The state when the field, and in general, field quanta exist with the lowest energy, is called vacuum. Particles of the electromagnetic field (photons) in a vacuum in a state of excitation lose the mechanical properties that they contain and which are inherent in corpuscular matter (for example, during movement the body does not feel friction). Vacuum does not contain simple types of matter, however, despite this, it is not emptiness in the true sense of the word, so in vacuum excitation quanta of the electromagnetic field arise - photons that realize electromagnetic mutual influence. In a vacuum, in addition to the electromagnetic field, there are other physical fields, including the gravitational field, which has not yet been noted in the so-called graviton experiments. A quantum field is a collection of quanta and is discrete in nature. Thus, the mutual influence of elementary particles, their mutual transformations, emission and absorption of photons is discrete in nature and occurs only in a situation of quantization. As a result, the following question arises: in what exactly is the continuity of the field, its continuity, manifested? In both quantum electrodynamics and quantum mechanics, the field state is described unambiguously not by observable real phenomena, but only by a wave function associated with the reciprocal concept. The square of the modulus of this function shows the ability to observe the physical phenomena under consideration. The main problem of quantum field theory is the description of various types of mutual influences of particles in the corresponding equations. This problem has so far found its solution only in quantum electrodynamics, which describes the mutual influences of electrons, positrons and photons. Quantum field theory has not yet been created for strong and weak mutual influences. Currently, these types of mutual influence are not described using strict methods. Although it is known that it is impossible to understand elementary particles if they are not in the corresponding physical theory, it is impossible to understand their structure, determined by the structure of these theories. Therefore, the problem of the structure of elementary particles has not yet been fully resolved. Modern physics is currently proving the existence of complex particles that have the internal structure of particles considered “elementary”. It became known that the proton and neutron, as a result of the virtual processes occurring in them, undergo internal transformations. As a result of experiments carried out to study the structure of protons, it was determined that the proton, which until recently was considered indivisible, the simplest and most structureless, is in fact a complex particle. At its center there is a dense core called the “core”, it is surrounded by positive pi mesons. The complexity of the structure of “elementary” particles was proven by the quark hypothesis put forward in 1964 by the American scientist Hel-Mann and independently by the Swedish scientist Zweig. According to this hypothesis, elementary particles with relationships characterized by strong mutual influences (hadrons: proton, neutron, hyperons) should be formed from quark particles whose charge is equal to one-third or two-thirds of the electron charge. Thus, the theory shows that the electric and baryon charges of the marked quarks that form the particles should be expressed as a fractional number. Indeed, particles called quarks have not yet been discovered and remain hypothetical inhabitants of the microworld at the current level of scientific development.

Conclusion

Thus, on the one hand, it is clear that elementary particles have a special structure, on the other hand, the nature of this structure still remains unclear. From the above data it becomes clear that elementary particles are not elementary at all, they have an internal structure and can be divided and transformed into each other. We still know very little about both structures. Thus, today, based on a number of facts, we can claim that the matter of elementary particles is a new type, qualitatively different from more complex particles (nucleus, atom, molecule). At the same time, this difference is so significant that the categories and expressions we use when studying nuclei, atoms, molecules, macroscopic bodies (“simple” and “complex”, “internal structure”, “formed”) can also be applied to elementary particles. The concepts “simple and complex”, “component parts”, “structure”, “whole” are, in general, relative concepts. For example, despite the fact that an atom has a complex structure, and its structure consists of nuclear and electronic tiers, it is simpler in comparison with its constituent molecule. In the hierarchy of structures of material systems, the atomic nucleus, atom, molecule, and macroscopic bodies themselves create a single structural level. Therefore, the elements of the body, compared to the elements of the next level, are simpler and act as their constituent parts. On the other hand, they are more complex compared to the elements located at lower levels and being their components. All systems, starting from the nucleus of an atom to those very large sizes, have this property: in each of them it is possible to separate the structural elements that form the bodies under consideration and are simpler than elements at a lower level into their constituent parts. In terms of their meaning, the processes of consolidation and separation are the same. For example, the molecules of a given chemical substance consist of a certain number of atoms and can break down into them under certain conditions. In this case, the mass of the complex whole is greater than the mass of each of its constituent parts. This last position is not true for elementary particles. Thus, the decay products of elementary particles are not simpler than divisible, yet exact “transforming” particles. They are also elementary particles. According to modern concepts, decay products, together with the particles that generate them, are located at a single level of hierarchy. For example, a neutron under certain conditions is divided into a proton, an electron and an antineutron (n0 ®p+ + e- +). Although the neutron is no more complex or simpler than the proton, electron and antineutron. In addition, a proton and an electron can be obtained as a result of other reactions. Therefore, we can say that the possibility of each elementary particle is that it can be a “component” of other elementary particles. On the other hand, it is not so important that at each elementary level the whole should consist of such a large accumulation. In this case, the mass of the whole can be even several times less than the masses of its components. For example, in a number of cases, as a result of the merging of a nyuklon and an antinyuklon, a meson is obtained whose mass is less than the mass of either of them. This anomaly is explained by the fact that during the creation of an elementary particle, the mass absorbing the released energy

can be so large that the resulting reaction products are not at all similar to the original particle. Therefore, in the world of elementary particles, the concepts “simple and complex”, “component”, “structure”, “whole” acquire a completely different meaning than in atomic physics and classical physics. The specificity of elementary particles is also manifested in energetic mutual influences. Starting with macroscopic objects and ending with the nucleus of an atom, the energy of all material systems is formed from two components: a special one corresponding to the mass of the body (E=mc2) and the binding energy of its constituent elements. Although these types of energy are inseparable from each other, they are completely different in nature. The special energy of objects is much greater than the energy of their connection; it can be separated into all its constituent parts. For example, due to external energy, a molecule can be divided into atoms (H2O®H+O+H), but in this case a noticeable change will not occur in the atoms themselves. In elementary particles this problem takes on a different form. All the energy of elementary particles is not divided into special and binding. Therefore, despite the fact that elementary particles do not have an internal structure, they cannot be divided into their constituent parts. Elementary particles do not contain internal particles that remain more or less unchanged. According to modern concepts, the structure of elementary particles is described by means of continuously generated and continuously dividing “virtual” particles. For example, meson annihilation (from the Latin word “annihilatio” - destruction) is formed from continuously created and then disappearing virtual nucleons and virtual antinucleons. Formal advancement of the concept of a virtual particle shows that the internal structure of elementary particles cannot be described by means of other particles. A theory of the origin and structure of elementary particles that satisfies physicists has not yet been created. A number of prominent scientists came to the idea that this theory could be created taking into account only cosmic conditions. The idea of ​​the generation of elementary particles from vacuum in force, electromagnetic and gravitational fields is acquiring significant significance. Because the relationship between the micro, macro and mega worlds is embodied only in this idea. In the megaworld, the structure and mutual transformations of elementary particles are determined by fundamental mutual influences. It is obvious that in order to adequately describe the structure of the material world, it is necessary to develop a apparatus of new concepts.

Bibliography

1. Makovelsky. Ancient Greek atomists. Baku, 1946.

2. Kudryavtsev. Course on the history of physics. M., Education, 1974, p.179.

3. Philosophy of natural science. M., 1966, p.45; E.M. Balabanov. Into the depths of the atom, M., 1967.

4. Philosophy and natural science. M., 1964, pp. 74-75; S.T. Melyukhin. Towards a philosophical assessment of modern concepts of field and matter. In the book: Dialectical materialism and modern natural science, M., 1957, p. 124-127.

5. Kuznetsov B. Paths of physical thought. Ed. "Science", M., 1968, p. 296-298

6. Akhizer A.I., Rekalo M.P. Biography of elementary particles, Kyiv, 1978.

7. Stanyukovich K.P., Lapchinsky V.G. Systematics of elementary particles.

8. In the Book: On the systematics of particles, M., 1969, pp. 74-75.

9. Balabanov E.M. Deep into the atom. M., 1967, pp. 38-39.

10. Novozhilov Yu.V. Elementary particles. M., 1974; Sproul R. Modern physics. M., 1974;

11. Soddy F. History of atomic energy. M., 1979.

12. Gott V.S. About the inexhaustibility of the material world. M., “Knowledge”, 1968, p.31.

13. Knyazev V.N. Concepts of interaction in modern physics. M.

14. Svechnikov G.A. Infinity of matter. M., 1965, p. 17-21; Omelyanovsky M

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Federal State Educational Institution

higher professional education

"SOUTH FEDERAL UNIVERSITY"

Faculty of Economics

Elementary particles.

Their classification and main properties.

Performed

1st year student, 11th group

Bublikova Ekaterina

Rostov-on-Don – 2009

Introduction. The world of elementary particles.

Fundamental physical interactions.

1. Gravity.

   Electromagnetic interaction.

   Weak interaction.

   Strong interaction.

Classification of elementary particles.

1. Characteristics of subatomic particles.

   History of the discovery of elementary particles.

2.5. Quark theory.

2.6. Particles are carriers of interactions.

3. Theories of elementary particles.

3.1. Quantum electrodynamics.

3.2. Theory of electroweak interaction.

3.3. Quantum chromodynamics.

3.4. On the way to... The Great Unification.

List of used literature.

The world of elementary particles.

In the middle and second half of the twentieth century, truly amazing results were obtained in those branches of physics that study the fundamental structure of matter. First of all, this manifested itself in the discovery of a whole host of new subatomic particles. They are usually called elementary particles, but not all of them are truly elementary. Elementary particles in the precise meaning of this term are primary, further indecomposable particles, of which all matter is supposed to consist, but many of them, in turn, consist of even more elementary particles.

The world of subatomic particles is truly diverse. Currently, more than 350 elementary particles are known. These include protons and neutrons that make up atomic nuclei, as well as electrons orbiting the nuclei. But there are also particles that are practically never found in the matter around us. If the average lifetime of a neutron located outside the atomic nucleus is 15 minutes, then the lifetime of such short-lived particles is extremely short, it amounts to the smallest fractions of a second. After this extremely short time, they disintegrate into ordinary particles. There are an amazing number of such unstable short-lived particles: several hundred of them are already known. However, it cannot be considered that unstable elementary particles “consist” of stable ones, if only because the same particle can decay in several ways into different elementary particles.

Each elementary particle (with the exception of absolutely neutral particles) has its own antiparticle.

Physicists discovered the existence of elementary particles when studying nuclear processes, so until the middle of the 20th century, elementary particle physics was a branch of nuclear physics. Currently, elementary particle physics and nuclear physics are close but independent branches of physics, united by the commonality of many problems considered and the research methods used. The main task of elementary particle physics is the study of the nature, properties and mutual transformations of elementary particles.

In the 1960s and 1970s, physicists were completely baffled by the number, variety, and strangeness of the newly discovered subatomic particles. There seemed to be no end to them. It is completely unclear why there are so many particles. Are these elementary particles chaotic and random fragments of matter? Or perhaps they hold the key to understanding the structure of the Universe? The development of physics in subsequent decades showed that there is no doubt about the existence of such a structure. At the end of the twentieth century, physics begins to understand the significance of each of the elementary particles.

The world of subatomic particles is characterized by a deep and rational order. This order is based on fundamental physical interactions.

1. Fundamental physical interactions.

In his daily life, a person is faced with many forces acting on his body. Here is the force of the wind or the oncoming flow of water, air pressure, a powerful release of explosive chemicals, human muscular strength, the weight of heavy objects, the pressure of light quanta, the attraction and repulsion of electrical charges, seismic waves that sometimes cause catastrophic destruction, and volcanic eruptions that led to the death of civilization, etc. Some forces act directly upon contact with the body, others, for example, gravity, act at a distance, through space. But, as it turned out as a result of the development of theoretical natural science, despite such great diversity, all forces acting in nature can be reduced to just four fundamental interactions: gravitational, electromagnetic, weak and strong. It is these interactions that are ultimately responsible for all changes in the world; they are the source of all transformations of bodies and processes. Elementary particles are divided into groups according to their abilities for various types of fundamental interactions. The study of the properties of fundamental interactions is the main task of modern physics.

1.1. Gravity.

In the history of physics, gravity (gravity) became the first of the four fundamental interactions to be the subject of scientific research. After its appearance in the 17th century. Newton's theory of gravity - the law of universal gravitation - managed for the first time to realize the true role of gravity as a force of nature. Gravity has a number of features that distinguish it from other fundamental interactions.

The most surprising feature of gravity is its low intensity. The magnitude of the gravitational interaction between the components of a hydrogen atom is 10n, where n = -39, based on the force of interaction of electric charges. It may seem surprising that we feel gravity at all, since it is so weak. How can she become the dominant force in the Universe?

It's all about the second amazing feature of gravity - its universality. Nothing in the Universe is free from gravity. Each particle experiences the action of gravity and is itself a source of gravity. Since every particle of matter exerts a gravitational pull, gravity increases as larger clumps of matter form. We feel gravity in everyday life because all the atoms of the Earth work together to attract us. And although the effect of the gravitational attraction of one atom is negligible, the resulting force of attraction from all atoms can be significant.

Gravity - long-range force of nature. This means that, although the intensity of gravitational interaction decreases with distance, it spreads in space and can affect bodies very distant from the source. On an astronomical scale, gravitational interactions tend to play a major role. Thanks to long-range action, gravity prevents the Universe from falling apart: it holds planets in orbits, stars in galaxies, galaxies in clusters, clusters in the Metagalaxy.

The gravitational force acting between particles is always an attractive force: it tends to bring the particles closer together. Gravitational repulsion has never been observed before (although in the traditions of quasi-scientific mythology there is a whole field called levitation - the search for the "facts" of antigravity). Since the energy stored in any particle is always positive and gives it positive mass, particles under the influence of gravity always tend to get closer.

What is gravity, a certain field or a manifestation of the curvature of space-time - there is still no clear answer to this question. There are different opinions and concepts of physicists on this matter.

1.2. Electromagnetic interaction.

Electrical forces are much larger than gravitational forces. Unlike the weak gravitational interaction, the electrical forces acting between bodies of normal size can be easily observed. Electromagnetism has been known to people since time immemorial (auroras, lightning flashes, etc.).

For a long time, electrical and magnetic processes were studied independently of each other. A decisive step in the knowledge of electromagnetism was made in the middle of the 19th century by J. C. Maxwell, who united electricity and magnetism in a unified theory of electromagnetism - the first unified field theory.

The existence of the electron was firmly established in the 90s of the last century. It is now known that the electric charge of any particle of matter is always a multiple of the fundamental unit of charge - a kind of “atom” of charge. Why this is so is an extremely interesting question. However, not all material particles are carriers of electric charge. For example, the photon and neutrino are electrically neutral. In this respect, electricity differs from gravity. All material particles create a gravitational field, while only charged particles are associated with an electromagnetic field. The carrier of electromagnetic interaction between charged particles is the electromagnetic field, or field quanta - photons.

Like electric charges, like magnetic poles repel, and opposite ones attract. However, unlike electric charges, magnetic poles do not occur individually, but only in pairs - a north pole and a south pole. Since ancient times, attempts have been known to obtain, by dividing a magnet, only one isolated magnetic pole - a monopole. But they all ended in failure. Perhaps the existence of isolated magnetic poles in nature is excluded? There is no definite answer to this question yet. Some theoretical concepts allow for the possibility of a monopole.

Like electrical and gravitational interactions, the interaction of magnetic poles obeys the inverse square law. Consequently, electric and magnetic forces are “long-range”, and their effect is felt at large distances from the source. Thus, the Earth's magnetic field extends far into outer space. The Sun's powerful magnetic field fills the entire Solar System. There are also galactic magnetic fields.

Electromagnetic interaction determines the structure of atoms and is responsible for the vast majority of physical and chemical phenomena and processes. Electromagnetic interaction also leads to the emission of electromagnetic waves.

1.3. Weak interaction.

Physics has moved slowly towards identifying the existence of the weak interaction. The weak force is responsible for particle decays, and its manifestation was therefore confronted with the discovery of radioactivity and the study of beta decay.

Beta decay has revealed an extremely strange feature. Research led to the conclusion that this decay violates one of the fundamental laws of physics - the law of conservation of energy. It seemed that in this decay part of the energy disappeared somewhere. In order to “save” the law of conservation of energy, W. Pauli suggested that, together with the electron, during beta decay, another particle flies out. It is neutral and has an unusually high penetrating ability, as a result of which it could not be observed. E. Fermi called the invisible particle "neutrino".

Neutrino (Italian neutrino, diminutive of neutrone - neutron), a stable uncharged elementary particle with spin 1/2 and possibly zero mass. Neutrinos are classified as leptons. They participate only in weak and gravitational interactions and therefore interact extremely weakly with matter. There are electron neutrinos, always paired with an electron or positron, muon neutrinos, paired with a muon, and tau neutrinos, associated with a heavy lepton. Each type of neutrino has its own antiparticle, which differs from neutrinos in the sign of the corresponding lepton charge and helicity: neutrinos have left-handed helicity (spin is directed against the motion of the particle), and antineutrinos have right-handed helicity (spin is in the direction of motion).

But the prediction and detection of neutrinos is only the beginning of the problem, its formulation. It was necessary to explain the nature of neutrinos, but there remained a lot of mystery here. The fact is that both electrons and neutrinos were emitted by unstable nuclei. But it was irrefutably proven that there are no such particles inside nuclei. How did they arise? It was suggested that electrons and neutrinos do not exist in the nucleus in a “ready form”, but are somehow formed from the energy of the radioactive nucleus. Further research showed that the neutrons included in the nucleus, left to their own devices, after a few minutes decay into a proton, electron and neutrino, i.e. instead of one particle, three new ones appear. The analysis led to the conclusion that known forces could not cause such a disintegration. It was apparently generated by some other, unknown force. Research has shown that this force corresponds to some weak interaction.

It is much weaker than electromagnetic, although stronger than gravitational. It spreads over very short distances. The radius of weak interaction is very small and is about 2*10^(-16) cm. The weak interaction stops at a minimum distance from the source and therefore cannot affect macroscopic objects, but is limited to individual subatomic particles. All elementary particles except the photon participate in weak interaction. It determines most of the decays of elementary particles, the interaction of neutrinos with matter, etc. The weak interaction is characterized by a violation of parity, strangeness, and “charm.” A unified theory of weak and electromagnetic interaction was created in the late 60s by S. Weinberg, S. Glashow and A. Salam. It describes the interactions of quarks and leptons, carried out through the exchange of four particles: massless photons (electromagnetic interaction) and heavy intermediate vector bosons - particles W+, W- and Z°, which are carriers of the weak interaction (experimentally discovered in 1983). This single interaction came to be called electroweak. Since Maxwell's theory of the electromagnetic field, the creation of this theory was the largest step towards the unity of physics.

1.4. Strong interaction.

The last in the series of fundamental interactions is the strong interaction, which is a source of enormous energy. The most typical example of energy released by the strong force is our Sun. In the depths of the Sun and stars, starting from a certain time, thermonuclear reactions caused by strong interaction continuously occur. But man has also learned to release strong interactions: a hydrogen bomb has been created, technologies for controlled thermonuclear reactions have been designed and improved.

Physics came to the idea of ​​the existence of strong interaction during the study of the structure of the atomic nucleus. Some force must hold the protons in the nucleus, preventing them from scattering under the influence of electrostatic repulsion. Gravity is too weak for this; Obviously, some new interaction is needed, moreover, stronger than electromagnetic. It was subsequently discovered. It turned out that although the strong interaction significantly exceeds all other fundamental interactions in its magnitude, it is not felt outside the nucleus. The radius of action of the new force turned out to be very small. The strong force drops off sharply at a distance from a proton or neutron greater than about 10^(-15) m.

In addition, it turned out that not all particles experience strong interactions. It is experienced by protons and neutrons, but electrons, neutrinos and photons are not subject to it. This means that only hadrons participate in the strong interaction.

The strong interaction exceeds the electromagnetic interaction by about 100 times. The theoretical explanation of the nature of the strong interaction has been difficult to develop. A breakthrough occurred in the early 60s, when the quark model was proposed. In this theory, neutrons and protons are considered not as elementary particles, but as composite systems built from quarks. The modern theory of the strong interaction is quantum chromodynamics.

Thus, in fundamental physical interactions the difference between long-range and short-range forces is clearly visible. On the one hand, there are interactions of unlimited range (gravity, electromagnetism), and on the other, interactions of short range (strong and weak). The world of physical elements as a whole unfolds in the unity of these two polarities and is the embodiment of the unity of the extremely small and the extremely large - short-range action in the microworld and long-range action throughout the Universe.

1.5. The problem of the unity of physics.

Knowledge is a generalization of reality, and therefore the goal of science is the search for unity in nature, linking disparate fragments of knowledge into a single picture. In order to create a unified system, it is necessary to open a connecting link between various branches of knowledge, some fundamental relationship. The search for such connections and relationships is one of the main tasks of scientific research. Whenever it is possible to establish such new connections, the understanding of the surrounding world deepens significantly, new ways of knowing are formed that point the way to previously unknown phenomena.

Establishing deep connections between different areas of nature is both a synthesis of knowledge and a method that guides scientific research along new, untrodden roads. Newton's discovery of the connection between the attraction of bodies under terrestrial conditions and the movement of planets marked the birth of classical mechanics, on the basis of which the technological basis of modern civilization is built. The establishment of a connection between the thermodynamic properties of gas and the chaotic movement of molecules put the atomic-molecular theory of matter on a solid basis. In the middle of the last century, Maxwell created a unified electromagnetic theory that covered both electrical and magnetic phenomena. Then, in the 20s of the twentieth century, Einstein made attempts to combine electromagnetism and gravity in a single theory.

But by the middle of the twentieth century, the situation in physics had changed radically: two new fundamental interactions were discovered - strong and weak, i.e. when creating a unified physics, one has to take into account not two, but four fundamental interactions. This somewhat cooled the ardor of those who hoped for a quick solution to this problem. But the idea itself was not seriously questioned, and the enthusiasm for the idea of ​​a single description did not go away.

There is a point of view that all four (or at least three) interactions represent phenomena of the same nature and their unified theoretical description must be found. The prospect of creating a unified theory of the world of physical elements based on a single fundamental interaction remains very attractive. This is the main dream of physicists of the twentieth century. But for a long time it remained only a dream, and a very vague one.

However, in the second half of the twentieth century, the prerequisites for the realization of this dream and the confidence that this is not a matter of the distant future appeared. It looks like it could soon become a reality. A decisive step towards a unified theory was made in the 60-70s with the creation first of the theory of quarks, and then of the theory of electroweak interaction. There is reason to believe that we are on the threshold of a more powerful and deeper unification than ever before. There is a growing belief among physicists that the contours of a unified theory of all fundamental interactions - the Grand Unification - are beginning to emerge.

2. Classification of elementary particles.

2.1. Characteristics of subatomic particles.

The discovery at the turn of the nineteenth and twentieth centuries of the smallest carriers of the properties of matter - molecules and atoms - and the establishment of the fact that molecules are built from atoms, for the first time made it possible to describe all known substances as combinations of a finite, albeit large, number of structural components - atoms. Further identification of the presence of constituent atoms - electrons and nuclei, establishment of the complex nature of nuclei, which turned out to be built from only two types of particles (protons and neutrons) , significantly reduced the number of discrete elements that form the properties of matter. It is impossible to say with certainty that particles that are elementary in the sense of the above definition exist. Protons and neutrons, for example, which for a long time were considered elementary, as it turned out, have a complex structure. The possibility cannot be ruled out that the sequence of structural components of matter is fundamentally infinite. It may also turn out that the statement “consists of...” at some stage of the study of matter will turn out to be devoid of content. In this case, the definition of “elementary” given above will have to be abandoned. The existence of elementary (subatomic) particles is a kind of postulate, and testing its validity is one of the most important tasks of physics.

The characteristics of subatomic particles are mass, electric charge, spin (intrinsic angular momentum), particle lifetime, magnetic moment, spatial parity, charge parity, lepton charge, baryon charge, strangeness, “charm”, etc.

When they talk about the mass of a particle, they mean its rest mass, since this mass does not depend on the state of motion. A particle with zero rest mass moves at the speed of light (photon). No two particles have the same mass. The electron is the lightest particle with a non-zero rest mass. The proton and neutron are almost 2000 times heavier than the electron. And the heaviest known elementary particle (Z - particle) has a mass 200,000 times the mass of an electron.

The electric charge varies over a fairly narrow range and is always a multiple of the fundamental unit of charge - the charge of the electron (-1). Some particles, such as the photon and neutrino, have no charge at all.

An important characteristic of a particle is spin. It has no classical analogue and, of course, indicates the “internal complexity” of a microobject. True, sometimes they try to compare with the concept of spin a model of an object rotating around its axis (the word “spin” itself is translated as “spindle”). This model is visual, but incorrect. In any case, it cannot be taken literally. The term “rotating microobject” found in the literature does not mean the rotation of the microobject, but only the presence of a specific internal angular momentum. In order for this moment to “turn” into the classical angular momentum (and thus the object would actually begin to rotate), it is necessary to require the fulfillment of the condition s >> 1 (much more than one). However, this condition is never met. The spin is also always a multiple of some fundamental unit, which is chosen to be ½. All particles of the same type have the same spin. Typically, particle spins are measured in units of Planck's constant ћ. It can be an integer (0, 1, 2,...) or a half-integer (1/2, 3/2,...). Thus, a proton, neutron and electron have a spin of S, and the spin of a photon is equal to 1. Particles with a spin of 0, 3/2, 2 are known. A particle with a spin of 0 looks the same at any angle of rotation. Particles with spin 1 take the same form after a full rotation of 360°. A particle with spin 1/2 takes on its previous appearance after a rotation of 720°, etc. A particle with spin 2 returns to its previous position after half a turn (180°). Particles with a spin greater than 2 have not been detected, and perhaps they do not exist at all. Knowing the spin of a microobject allows us to judge the nature of its behavior in a group of its own kind (in other words, it allows us to judge the statistical properties of the microobject). It turns out that, according to their statistical properties, all microobjects in nature are divided into two groups: a group of microobjects with an integer spin and a group of microobjects with a half-integer spin.

Microobjects of the first group are capable of “populating” the same state in an unlimited number, and the more strongly this state is “populated,” the higher the number. Such microobjects are said to obey Bose-Einstein statistics. For short, they are simply called bosons. Microobjects of the second group can “populate” states only one by one. And if the state in question is occupied, then no microobject of this type can get into it. Such micro-objects are said to obey Fermi-Dirac statistics, and for brevity they are called fermions. Of the elementary particles, bosons include photons and mesons, and fermions include leptons (in particular electrons), nucleons, and hyperons.

Particles are also characterized by their lifetime. Based on this criterion, particles are divided into stable and unstable. Stable particles are the electron, proton, photon and neutrino. A neutron is stable when in the nucleus of an atom, but a free neutron decays in about 15 minutes. All other known particles are unstable, their lifetime ranges from a few microseconds to 10n seconds (where n = -23). This means that when this time expires, they spontaneously, without any external influences, disintegrate, turning into other particles. For example, a neutron spontaneously decays into a proton, an electron, and an electron antineutrino. It is impossible to predict exactly when the indicated decay of a particular neutron will occur, because each specific decay event is random. Each unstable elementary particle is characterized by its own lifetime. The shorter the lifetime, the greater the probability of particle decay. Instability is inherent not only in elementary particles, but also in other micro-objects. The phenomenon of radioactivity (spontaneous transformation of isotopes of one chemical element into isotopes of another, accompanied by the emission of particles) shows that atomic nuclei can be unstable. Atoms and molecules in excited states also turn out to be unstable: they spontaneously go into the ground or less excited state.

Instability, determined by probabilistic laws, is, along with the presence of spin, the second highly specific property inherent in microobjects. It can also be considered as an indication of a certain “internal complexity” of a micro-object.

However, instability is a specific, but by no means obligatory, property of a microobject. Along with unstable ones, there are many stable micro-objects: photon, electron, proton, neutrino, stable atomic nuclei, as well as atoms and molecules in the ground state.

Lepton charge (lepton number) is an internal characteristic of leptons. It is designated by the letter L. For leptons it is +1, and for antileptons -1. There are: electronic lepton charge, which is possessed only by electrons, positrons, electron neutrinos and antineutrinos; muonic lepton charge, which is possessed only by muons and muon neutrinos and antineutrinos; lepton charge of heavy leptons and their neutrinos. The algebraic sum of the lepton charge of each type is conserved with very high accuracy across all interactions.

Baryon charge (baryon number) is one of the internal characteristics of baryons. Denoted by the letter B. All baryons have B = +1, and their antiparticles have B = -1 (for other elementary particles B = 0). The algebraic sum of baryon charges included in a system of particles is conserved under all interactions.

Strangeness is an integer (zero, positive or negative) quantum number that characterizes hadrons. The strangeness of particles and antiparticles is opposite in sign. Hadrons with S equal to 0 are called strange. Strangeness is preserved in the strong and electromagnetic interactions, but is violated in the weak interaction.

“Charm” (charm) is a quantum number characterizing hadrons (or quarks). It is preserved in the strong and electromagnetic interactions, but is violated by the weak interaction. Particles with a non-zero charm value are called "charmed" particles.

Magneton is a unit of measurement of magnetic moment in the physics of the atom, atomic nucleus and elementary particles. The magnetic moment, caused by the orbital motion of electrons in an atom and their spin, is measured in Bohr magnetons. The magnetic moment of nucleons and nuclei is measured in nuclear magnetons.

Parity is another characteristic of subatomic particles. Parity is a quantum number that characterizes the symmetry of the wave function of a physical system or an elementary particle under some discrete transformations: if during such a transformation the function does not change sign, then the parity is positive; if it does, then the parity is negative. For absolutely neutral particles (or systems) that are identical to their antiparticles, in addition to spatial parity, one can introduce the concepts of charge parity and combined parity (for other particles, replacing them with antiparticles changes the wave function itself).

Spatial parity is a quantum mechanical characteristic that reflects the symmetry properties of elementary particles or their systems during mirror reflection (spatial inversion). This parity is denoted by the letter P and is conserved in all interactions except weak ones.

Charge parity - the parity of an absolute neutral elementary particle or system, corresponding to the operation of charge conjugation. Charge parity is also conserved in all interactions except weak ones.

Combined parity is the parity of an absolutely neutral particle (or system) relative to the combined inversion. Combined parity is conserved in all interactions, with the exception of decays of the long-lived neutral K meson caused by the weak interaction (the reason for this violation of combined parity has not yet been clarified).

2.2. History of the discovery of elementary particles.

The idea that the world is made of fundamental particles has a long history. For the first time, the idea of ​​the existence of the smallest invisible particles that make up all surrounding objects was expressed 400 years BC by the Greek philosopher Democritus. He called these particles atoms, that is, indivisible particles. Science began to use the idea of ​​atoms only at the beginning of the 19th century, when on this basis it was possible to explain a number of chemical phenomena. In the 30s of the 19th century, in the theory of electrolysis developed by M. Faraday, the concept of an ion appeared and the elementary charge was measured. But from about the middle of the 19th century, experimental facts began to appear that cast doubt on the idea of ​​​​the indivisibility of atoms. The results of these experiments suggested that atoms have a complex structure and that they contain electrically charged particles. This was confirmed by the French physicist Henri Becquerel, who discovered the phenomenon of radioactivity in 1896.

This was followed by the discovery of the first elementary particle by the English physicist Thomson in 1897. It was the electron that finally acquired the status of a real physical object and became the first known elementary particle in human history. Its mass is approximately 2000 times less than the mass of a hydrogen atom and is equal to:

m = 9.11*10^(-31) kg.

The negative electric charge of an electron is called elementary and is equal to:

e = 0.60*10^(-19) Cl.

Analysis of atomic spectra shows that the electron spin is equal to 1/2, and its magnetic moment is equal to one Bohr magneton. Electrons obey Fermi statistics because they have half-integer spin. This is consistent with experimental data on the structure of atoms and the behavior of electrons in metals. Electrons participate in electromagnetic, weak and gravitational interactions.

The second discovered elementary particle was the proton (from the Greek protos - first). This elementary particle was discovered in 1919 by Rutherford, while studying the products of fission of atomic nuclei of various chemical elements. Literally, a proton is the nucleus of an atom of the lightest isotope of hydrogen - protium. The proton spin is 1/2. A proton has a positive elementary charge +e. Its mass is:

m = 1.67*10^(-27) kg.

or approximately 1836 electron masses. Protons are part of the nuclei of all atoms of chemical elements. After this, in 1911, Rutherford proposed a planetary model of the atom, which helped scientists in further research into the composition of atoms.

In 1932, J. Chadwick discovered the third elementary particle, the neutron (from the Latin neuter - neither one nor the other), which has no electrical charge and has a mass of approximately 1839 times the mass of an electron. The neutron spin is also 1/2.

The conclusion about the existence of a particle of an electromagnetic field - a photon - originates from the work of M. Planck (1900). Assuming that the energy of electromagnetic radiation from an absolutely black body is quantized (i.e., consists of quanta), Planck obtained the correct formula for the radiation spectrum. Developing Planck's idea, A. Einstein (1905) postulated that electromagnetic radiation (light) is actually a flow of individual quanta (photons), and on this basis explained the laws of the photoelectric effect. Direct experimental evidence of the existence of the photon was given by R. Millikan in 1912 - 1915 and A. Compton in 1922.

The discovery of the neutrino, a particle that hardly interacts with matter, dates back to W. Pauli’s theoretical guess in 1930, which, due to the assumption of the birth of such a particle, made it possible to eliminate difficulties with the law of conservation of energy in the beta decay processes of radioactive nuclei. The existence of neutrinos was experimentally confirmed only in 1953 by F. Reines and K. Cowan.

But matter consists of more than just particles. There are also antiparticles - elementary particles that have the same mass, spin, lifetime and some other internal characteristics as their “twins” - particles, but differ from particles in the signs of electric charge and magnetic moment, baryon charge, lepton charge, strangeness and etc. All elementary particles, except absolutely neutral ones, have their own antiparticles.

The first discovered antiparticle was the positron (from the Latin positivus - positive) - a particle with the mass of an electron, but a positive electric charge. This antiparticle was discovered in cosmic rays by American physicist Carl David Anderson in 1932. Interestingly, the existence of the positron was theoretically predicted by the English physicist Paul Dirac almost a year before the experimental discovery. Moreover, Dirac predicted the so-called processes of annihilation (disappearance) and the birth of an electron-positron pair. The annihilation of a pair itself is one of the types of transformations of elementary particles that occurs when a particle collides with an antiparticle. During annihilation, a particle and an antiparticle disappear, turning into other particles, the number and type of which are limited by conservation laws. The reverse process of annihilation is the birth of a couple. The positron itself is stable, but in matter it exists for a very short time due to annihilation with electrons. The annihilation of an electron and a positron is that when they meet, they disappear, turning into γ- quanta (photons). And in a collision γ- When a quantum occurs with any massive nucleus, an electron-positron pair is born.

In 1955, another antiparticle was discovered - the antiproton, and a little later - the antineutron. An antineutron, like a neutron, has no electrical charge, but it undoubtedly belongs to antiparticles, since it participates in the process of annihilation and the birth of a neutron-antineutron pair.

The possibility of obtaining antiparticles led scientists to the idea of ​​​​creating antimatter. Antimatter atoms should be built in this way: in the center of the atom there is a negatively charged nucleus, consisting of antiprotons and antineutrons, and positrons with a positive charge revolve around the nucleus. In general, the atom also turns out to be neutral. This idea received brilliant experimental confirmation. In 1969, at a proton accelerator in the city of Serpukhov, Soviet physicists obtained nuclei of antihelium atoms. Also in 2002, 50,000 antihydrogen atoms were produced at the CERN accelerator in Geneva. But, despite this, accumulations of antimatter in the Universe have not yet been discovered. It also becomes clear that at the slightest interaction of antimatter with any substance, their annihilation will occur, which will be accompanied by a huge release of energy, several times greater than the energy of atomic nuclei, which is extremely unsafe for people and the environment.

At present, antiparticles of almost all known elementary particles have been experimentally discovered.

A major role in the physics of elementary particles is played by conservation laws that establish equality between certain combinations of quantities characterizing the initial and final state of the system. The arsenal of conservation laws in quantum physics is larger than in classical physics. It was replenished with laws of conservation of various parities (spatial, charge), charges (leptonic, baryon, etc.), internal symmetries characteristic of one or another type of interaction.

Isolating the characteristics of individual subatomic particles is an important, but only the initial stage of understanding their world. At the next stage, we still need to understand what the role of each individual particle is, what its functions are in the structure of matter.

Physicists have found that, first of all, the properties of a particle are determined by its ability (or inability) to participate in strong interactions. Particles participating in strong interactions form a special class and are called hadrons. Particles that participate in the weak interaction and do not participate in the strong interaction are called leptons. In addition, there are particles that carry interactions.

2.3. Leptons.

Leptons are considered truly elementary particles. Although leptons may or may not have an electrical charge, they all have a spin of 1/2. Among leptons, the most famous is the electron. The electron is the first of the discovered elementary particles. Like all other leptons, the electron appears to be an elementary (in the proper sense of the word) object. As far as is known, the electron does not consist of any other particles.

Another well-known lepton is the neutrino. Neutrinos are the most common particles throughout the Universe. The Universe can be imagined as a boundless neutrino sea, in which islands in the form of atoms are occasionally found. But despite such prevalence of neutrinos, it is very difficult to study them. As we have already noted, neutrinos are almost elusive. Without participating in either strong or electromagnetic interactions, they penetrate through matter as if it were not there at all. Neutrinos are some kind of “ghosts of the physical world.”

Muons are quite widespread in nature, accounting for a significant portion of cosmic radiation. In many respects, the muon resembles an electron: it has the same charge and spin, participates in those interactions, but has a large mass (about 207 electron masses) and is unstable. In about two millionths of a second, the muon decays into an electron and two neutrinos. In the late 1970s, a third charged lepton was discovered, called the tau lepton. This is a very heavy particle. Its mass is about 3500 electron masses. But in all other respects it behaves like an electron and a muon.

In the 60s, the list of leptons expanded significantly. It was found that there are several types of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. Thus, the total number of neutrino varieties is three, and the total number of leptons is six. Of course, each lepton has its own antiparticle; thus the total number of different leptons is twelve. Neutral leptons participate only in weak interactions; charged - in the weak and electromagnetic. All leptons participate in gravitational interactions, but are not capable of strong ones.

2.4. Hadrons.

If there are just over a dozen leptons, then there are hundreds of hadrons. Such a multitude of hadrons suggests that hadrons are not elementary particles, but are built from smaller particles. All hadrons are found in two varieties - electrically charged and neutral. Among hadrons, the most famous and widespread are the neutron and proton, which in turn belong to the class of nucleons. The remaining hadrons are short-lived and decay quickly. Hadrons participate in all fundamental interactions. They are divided into baryons and mesons. Baryons include nucleons and hyperons.

To explain the existence of nuclear forces of interaction between nucleons, quantum theory required the existence of special elementary particles with a mass greater than the mass of the electron, but less than the mass of the proton. These particles, predicted by quantum theory, were later called mesons. Mesons were discovered experimentally. There turned out to be a whole family of them. All of them turned out to be short-lived unstable particles, living in a free state for billionths of a second. For example, a charged pi-meson or pion has a rest mass of 273 electron masses and a lifetime:

t = 2.6*10^(-8) s.

Further, during studies at charged particle accelerators, particles with masses exceeding the mass of a proton were discovered. These particles were called hyperons. Even more of them were discovered than mesons. The hyperon family includes: lambda-, sigma-, xi- and omega-minus hyperons.

The existence and properties of most known hadrons were established in accelerator experiments. The discovery of many different hadrons in the 50-60s greatly puzzled physicists. But over time, hadrons were classified by mass, charge and spin. Gradually a more or less clear picture began to emerge. Specific ideas emerged on how to systematize the chaos of empirical data and reveal the mystery of hadrons in scientific theory. The decisive step here was taken in 1963, when the theory of quarks was proposed.

2.5. Quark theory.

The theory of quarks is a theory of the structure of hadrons. The main idea of ​​this theory is very simple. All hadrons are made of smaller particles called quarks. This means that quarks are more elementary particles than hadrons. Quarks are hypothetical particles because were not observed in the free state. The baryon charge of quarks is 1/3. They carry a fractional electrical charge: they have a charge whose value is either -1/3 or +2/3 of the fundamental unit - the charge of the electron. A combination of two and three quarks can have a total charge of zero or one. All quarks have spin S, so they are classified as fermions. The founders of the theory of quarks, Gell-Mann and Zweig, in order to take into account all the hadrons known in the 60s, introduced three types (colors) of quarks: u (from up - upper), d (from down - lower) and s (from strange - strange) .

Quarks can combine with each other in one of two possible ways: either in triplets or in quark-antiquark pairs. Relatively heavy particles - baryons - are made up of three quarks. The best known baryons are the neutron and the proton. Lighter quark-antiquark pairs form particles called mesons - “intermediate particles”. For example, a proton consists of two u-quarks and one d-quark (uud), and a neutron consists of two d-quarks and one u-quark (udd). In order for this “trio” of quarks not to decay, a holding force, a certain “glue”, is needed.

It turns out that the resulting interaction between neutrons and protons in the nucleus is simply a residual effect of the more powerful interaction between the quarks themselves. This explained why strong interactions seem so complex. When a proton “sticks” to a neutron or another proton, the interaction involves six quarks, each of which interacts with all the others. A significant part of the force is spent on firmly gluing a trio of quarks, and a small part is spent on fastening two trios of quarks to each other. But later it turned out that quarks also participate in weak interactions. The weak interaction can change the color of a quark. This is how neutron decay occurs. One of the d-quarks in the neutron turns into a u-quark, and the excess charge carries away the electron that is born at the same time. Similarly, by changing the flavor, the weak interaction leads to the decay of other hadrons.

The fact that all known hadrons could be obtained from various combinations of the three fundamental particles was a triumph for the theory of quarks. But in the 70s, new hadrons were discovered (psi particles, upsilon meson, etc.). This dealt a blow to the first version of the quark theory, since there was no longer room for a single new particle in it. All possible combinations of quarks and their antiquarks have already been exhausted.

The problem was solved by introducing three new colors. They were named c - quark (charm), b - quark (from bottom - bottom, and more often beauty - beauty, or charm), and subsequently another color was introduced - t (from top - top).

Until now, quarks and antiquarks have not been observed in free form. However, there is practically no doubt about the reality of their existence. Moreover, a search is underway for “real” elementary particles following quarks - gluons, which are carriers of interactions between quarks, because Quarks are held together by the strong interaction, and gluons (color charges) are carriers of the strong interaction. The field of particle physics that studies the interaction of quarks and gluons is called quantum chromodynamics. Just as quantum electrodynamics is the theory of electromagnetic interaction, quantum chromodynamics is the theory of strong interaction. Quantum chromodynamics is a quantum field theory of the strong interaction of quarks and gluons, which is carried out through the exchange between them - gluons (analogues of photons in quantum electrodynamics). Unlike photons, gluons interact with each other, which leads, in particular, to an increase in the strength of interaction between quarks and gluons as they move away from each other. It is assumed that it is this property that determines the short-range action of nuclear forces and the absence of free quarks and gluons in nature.

According to modern concepts, hadrons have a complex internal structure: baryons consist of 3 quarks, mesons - of a quark and an antiquark.

Although there is some dissatisfaction with the quark scheme, most physicists consider quarks to be truly elementary particles - point-like, indivisible and without internal structure. In this respect they resemble leptons, and it has long been assumed that there must be a deep relationship between these two distinct but structurally similar families.

Thus, the most probable number of truly elementary particles (not counting carriers of fundamental interactions) at the end of the twentieth century is 48. Of these: leptons (6x2) = 12 and quarks (6x3)x2 = 36.

2.6. Particles are carriers of interactions.

The list of known particles is not limited to the listed particles - leptons and hadrons, which form the building material of matter. This list does not include, for example, a photon. There is also another type of particles that are not directly the building material of matter, but provide all four fundamental interactions, i.e. form a kind of “glue” that prevents the world from falling apart. Such particles are called carriers of interactions, and a particular type of particle transfers its interactions.

The carrier of electromagnetic interaction between charged particles is the photon. Photon is a quantum of electromagnetic radiation, a neutral particle with zero mass. The photon spin is 1.

The theory of electromagnetic interaction was introduced by quantum electrodynamics.

The carriers of the strong interaction are gluons. These are hypothetical electrically neutral particles with zero mass and spin 1. Like quarks, gluons have the quantum characteristic of “color.” Gluons are carriers of interaction between quarks, because tie them in pairs or threes.

The carriers of the weak interaction are three particles - W+, W- and Z° bosons. They were discovered only in 1983. The radius of the weak interaction is extremely small, so its carriers must be particles with large rest masses. According to the uncertainty principle, the lifetime of particles with such a large rest mass should be extremely short - only about 10n sec (where n = -26). The radius of interaction carried by these particles is very small because such short-lived particles do not have time to move very far.

It is suggested that the existence of a carrier of the gravitational field - the graviton - is also possible (in those theories of gravity that consider it not (only) as a consequence of the curvature of space-time, but as a field). Theoretically, a graviton is a quantum of the gravitational field, having zero rest mass, zero electric charge and spin 2. In principle, gravitons can be detected in experiment. But since the gravitational interaction is very weak and practically does not manifest itself in quantum processes, it is very difficult to directly detect gravitons, and so far no scientist has succeeded.

The classification of particles into leptons, hadrons and carriers of interactions exhausts the world of subatomic particles known to us. Each type of particle plays its role in shaping the structure of matter and the Universe.

3. Theories of elementary particles.

3.1. Quantum electrodynamics (QED).

Quantum theory combines quantum mechanics, quantum statistics and quantum field theory.

Quantum mechanics (wave mechanics) is a theory that establishes the method of description and laws of motion of microparticles in given external fields. It allows us to describe the movement of elementary particles, but not their generation or destruction, i.e., it is used only to describe systems with a constant number of particles. Quantum mechanics is one of the main branches of quantum theory. Quantum mechanics for the first time made it possible to describe the structure of atoms and understand their spectra, establish the nature of chemical bonds, explain the periodic system of elements, etc. Since the properties of macroscopic bodies are determined by the movement and interaction of the particles that form them, the laws of quantum mechanics underlie the understanding of most macroscopic phenomena. Thus, quantum mechanics made it possible to understand many properties of solids, explain the phenomena of superconductivity, ferromagnetism, superfluidity, and much more. Quantum mechanical laws underlie nuclear energy, quantum electronics, etc. Unlike classical theory, all particles act in quantum mechanics as carriers of both corpuscular and wave properties, which do not exclude, but complement each other. The wave nature of electrons, protons and other particles is confirmed by particle diffraction experiments. The state of a quantum system is described by a wave function, the square of the modulus of which determines the probability of a given state and, consequently, the probabilities for the values ​​of the physical quantities that characterize it. It follows from quantum mechanics that not all physical quantities can simultaneously have exact values. The wave function obeys the principle of superposition, which explains, in particular, the diffraction of particles. A distinctive feature of quantum theory is the discreteness of possible values ​​for a number of physical quantities: the energy of electrons in atoms, angular momentum and its projection onto an arbitrary direction, etc.; in classical theory, all these quantities can only change continuously. A fundamental role in quantum mechanics is played by Planck's constant - one of the main scales of nature, separating the areas of phenomena that can be described by classical physics from areas for the correct interpretation of which quantum theory is necessary. Planck's constant is named after M. Planck. It is equal to:

Ћ = h/2π ≈ 1.0546. 10 ^(-34) J. s

A generalization of quantum mechanics is quantum field theory - this is a quantum theory of systems with an infinite number of degrees of freedom (physical fields). Quantum field theory is the main apparatus of the physics of elementary particles, their interactions and interconversions. The need for such a theory is generated by quantum-wave dualism, the existence of wave properties in all particles. In quantum field theory, interaction is represented as a result of the exchange of field quanta. This theory includes the theory of electromagnetic (quantum electrodynamics) and weak interactions, which appear in modern theory as a single whole (electroweak interaction), and the theory of strong (nuclear) interaction (quantum chromodynamics).

Quantum statistics is the statistical physics of quantum systems consisting of a large number of particles. For particles with an integer spin, this is the Bose Einstein statistics, and for particles with a half-integer spin, this is the Fermi-Dirac statistics.

In the middle of the twentieth century, a theory of electromagnetic interaction was created - quantum electrodynamics QED - this is a theory of interaction between photons and electrons, thought out to the smallest detail and equipped with a perfect mathematical apparatus. QED is based on a description of electromagnetic interaction using the concept of virtual photons - its carriers. This theory satisfies the basic principles of both quantum theory and relativity.

At the center of the theory is the analysis of the acts of emission or absorption of one photon by one charged particle, as well as the annihilation of an electron-positron pair into a photon or the generation of such a pair by photons.

If in the classical description electrons are represented as a solid point ball, then in QED the electromagnetic field surrounding the electron is considered as a cloud of virtual photons that relentlessly follows the electron, surrounding it with energy quanta. After an electron emits a photon, it produces a (virtual) electron-positron pair, which can annihilate to form a new photon. The latter can be absorbed by the original photon, but can generate a new pair, etc. Thus, the electron is covered with a cloud of virtual photons, electrons and positrons, which are in a state of dynamic equilibrium. Photons appear and disappear very quickly, and electrons do not move in space along well-defined trajectories. It is still possible in one way or another to determine the starting and ending points of the path - before and after scattering, but the path itself in the interval between the beginning and end of the movement remains uncertain.

The description of interaction using a carrier particle led to an expansion of the concept of a photon. The concepts of a real (quantum of light visible to us) and a virtual (fleeting, ghostly) photon, which is “seen” only by charged particles undergoing scattering, are introduced.

To test whether the theory agreed with reality, physicists focused on two effects that were of particular interest. The first concerned the energy levels of the hydrogen atom, the simplest atom. According to QED, the levels should be slightly shifted relative to the position they would occupy in the absence of virtual photons. The second decisive test of QED concerned the extremely small correction to the electron's own magnetic moment. The theoretical and experimental results of testing QED coincide with the highest accuracy - more than nine decimal places. Such a striking correspondence gives the right to consider QED the most advanced of the existing natural scientific theories.

Following this triumph, QED was adopted as a model for the quantum description of the other three fundamental interactions. Of course, fields associated with other interactions must correspond to other carrier particles.

3.2. Theory of electroweak interaction.

In the 70s of the twentieth century, an outstanding event occurred in natural science: two fundamental interactions out of four physics were combined into one. The picture of the fundamental principles of nature has become somewhat simpler. Electromagnetic and weak interactions, seemingly very different in nature, actually turned out to be two varieties of a single electroweak interaction. The theory of electroweak interaction had a decisive influence on the further development of elementary particle physics at the end of the twentieth century.

The main idea in constructing this theory was to describe the weak interaction in the language of the concept of a gauge field, according to which the key to understanding the nature of interactions is symmetry. One of the fundamental ideas in physics of the second half of the twentieth century is the belief that all interactions exist only to maintain a certain set of abstract symmetries in nature. What does symmetry have to do with fundamental interactions? At first glance, the very assumption of the existence of such a connection seems paradoxical and incomprehensible.

First of all, about what is meant by symmetry. It is generally accepted that an object has symmetry if the object remains unchanged as a result of one or another operation to transform it. Thus, a sphere is symmetrical because it looks the same when rotated at any angle relative to its center. The laws of electricity are symmetrical regarding the replacement of positive charges with negative ones and vice versa. Thus, by symmetry we mean invariance under a certain operation.

There are different types of symmetries: geometric, mirror, non-geometric. Among the non-geometric ones there are so-called gauge symmetries. Gauge symmetries are abstract in nature and are not directly fixed. They are associated with a change in the reference level, scale or value of some physical quantity. A system has gauge symmetry if its nature remains unchanged under this kind of transformation. So, for example, in physics, work depends on the difference in heights, and not on the absolute height; voltage - from the potential difference, and not from their absolute values, etc. The symmetries on which the revision of the understanding of the four fundamental interactions is based are precisely of this kind. Gauge transformations can be global or local. Gauge transformations that vary from point to point are known as "local" gauge transformations. There are a number of local gauge symmetries in nature, and an appropriate number of fields are needed to compensate for these gauge transformations. Force fields can be considered as a means by which nature creates its inherent local gauge symmetry. The significance of the concept of gauge symmetry is that it theoretically models all four fundamental interactions found in nature. All of them can be considered as gauge fields.

Representing the weak interaction as a gauge field, physicists proceed from the fact that all particles participating in the weak interaction serve as sources of a new type of field - a field of weak forces. Weakly interacting particles, such as electrons and neutrinos, carry a “weak charge,” which is analogous to an electric charge and binds these particles to a weak field.

To represent the weak interaction field as a gauge field, it is first necessary to establish the exact form of the corresponding gauge symmetry. The fact is that the symmetry of the weak interaction is much more complex than the electromagnetic one. After all, the mechanism of this interaction itself turns out to be more complex. First, in the decay of a neutron, for example, the weak interaction involves particles of at least four different types (neutron, proton, electron and neutrino). Secondly, the action of weak forces leads to a change in their nature (the transformation of some particles into others due to weak interaction). On the contrary, electromagnetic interaction does not change the nature of the particles participating in it.

This determines the fact that the weak interaction corresponds to a more complex gauge symmetry associated with a change in the nature of the particles. It turned out that to maintain symmetry, three new force fields are needed here, as opposed to a single electromagnetic field. A quantum description of these three fields was also obtained: there should be three new types of particles - carriers of interaction, one for each field. Collectively they are called spin-1 heavy vector bosons and are carriers of the weak force.

W+ and W- particles are carriers of two of the three fields associated with the weak interaction. The third field corresponds to an electrically neutral carrier particle, called the Z particle. The existence of a Z particle means that the weak interaction may not be accompanied by electric charge transfer.

In the creation of the theory of electroweak interaction, the concept of spontaneous symmetry breaking played a key role: not every solution to a problem must have all the properties of its original level. Thus, particles that are completely different at low energies may actually turn out to be one and the same particle at high energies, but in different states. Based on the idea of ​​spontaneous symmetry breaking, the authors of the theory of electroweak interaction, Weinberg and Salam, were able to solve a great theoretical problem - they combined seemingly incompatible things: a significant mass of weak interaction carriers, on the one hand, and the idea of ​​gauge invariance, which assumes the long-range nature of the gauge field, and means zero rest mass of carrier particles, on the other hand. Thus, electromagnetism and the weak interaction were combined into a unified theory of the gauge field.

This theory presents only four fields: the electromagnetic field and three fields corresponding to weak interactions. In addition, a constant scalar field (a type of Higgs field) has been introduced throughout space, with which particles interact differently, which determines the difference in their masses. Scalar field quanta are new elementary particles with zero spin. They are called Higgs (named after the physicist P. Higgs, who suggested their existence). The number of such Higgs bosons can reach several dozen. Such bosons have not yet been experimentally discovered. Moreover, a number of physicists consider their existence unnecessary, but a perfect theoretical model without Higgs bosons has not yet been found. Initially, W and Z quanta have no mass, but symmetry breaking causes some Higgs particles to merge with W and Z particles, giving them mass.

The theory explains the differences in the properties of electromagnetic and weak interactions by breaking symmetry. If the symmetry were not broken, then both interactions would be comparable in magnitude. Symmetry breaking entails a sharp decrease in the weak interaction. We can say that the weak interaction is so small because the W and Z particles are very massive. Leptons rarely come together at such short distances (r 10n cm, where n = -16). But at high energies ( > 100 GeV), when W and Z particles can be freely produced, the exchange of W and Z bosons occurs as easily as the exchange of photons (massless particles). The difference between photons and bosons is erased. Under these conditions, there should be complete symmetry between the electromagnetic and weak interactions - the electroweak interaction.

Testing the new theory consisted of confirming the existence of the hypothetical W and Z particles. Their discovery became possible only with the creation of very large accelerators of the latest type. The discovery of W and Z particles in 1983 meant the triumph of the theory of electroweak interaction. There was no longer any need to talk about the four fundamental interactions. There are three of them left.

3.3. Quantum chromodynamics.

The next step on the path to the Great Unification of fundamental interactions is the merging of the strong interaction with the electroweak interaction. To do this, it is necessary to give the features of a gauge field to the strong interaction and introduce a generalized idea of ​​isotopic symmetry. The strong interaction can be thought of as the result of the exchange of gluons, which ensure the binding of quarks (in pairs or triplets) into hadrons.

The idea here is as follows. Each quark has an analogue of electric charge, which serves as a source of the gluon field. It was called a color (of course, this name has nothing to do with ordinary color). If the electromagnetic field is generated by a charge of only one type, then three different color charges were required to create a more complex gluon field. Each quark is “colored” in one of three possible colors, which were quite arbitrarily called red, green and blue. And accordingly, antiques are anti-red, anti-green and anti-blue.

At the next stage, the theory of strong interaction is developed according to the same scheme as the theory of weak interaction. The requirement of local gauge symmetry (i.e., invariance with respect to color changes at each point in space) leads to the need to introduce compensating force fields. A total of eight new compensating force fields are required. The carrier particles of these fields are gluons, and thus the theory implies that there must be as many as eight different types of gluons, while the carrier of the electromagnetic force is only one (photon), and the carriers of the weak force are three. Gluons have zero rest mass and spin 1. Gluons also have different colors, but not pure, but mixed (for example, blue-anti-green). Therefore, the emission or absorption of a gluon is accompanied by a change in the color of the quark (“play of colors”). So, for example, a red quark, losing a red-anti-blue gluon, turns into a blue quark, and a green quark, absorbing a blue-anti-green gluon, turns into a blue quark. In a proton, for example, three quarks constantly exchange gluons, changing their color. However, such changes are not arbitrary in nature, but are subject to a strict rule: at any moment of time, the “total” color of three quarks must be white light, i.e. the sum "red + green + blue". This also applies to mesons consisting of a quark-antiquark pair. Since an antiquark is characterized by an anticolor, such a combination is obviously colorless (“white”), for example, a red quark in combination with an antired quark forms a colorless meson.

From the point of view of quantum chromodynamics (quantum color theory), strong interaction is nothing more than the desire to maintain a certain abstract symmetry of nature: maintaining the white color of all hadrons while changing the color of their constituent parts. Quantum chromodynamics perfectly explains the rules that govern all combinations of quarks, the interaction of gluons with each other, the complex structure of a hadron consisting of quarks “dressed” in clouds, etc.

It may be premature to evaluate quantum chromodynamics as the final and complete theory of the strong interaction, but its achievements are nonetheless promising.

3.4. On the way to... The Great Unification.

With the creation of quantum chromodynamics, hope arose for the creation of a unified theory of all (or at least three out of four) fundamental interactions. Models that describe at least three of the four fundamental interactions in a unified way are called Grand Unified models. Theoretical schemes that combine all known types of interactions (strong, weak, electromagnetic and gravitational) are called supergravity models.

The experience of successfully combining weak and electromagnetic interactions based on the idea of ​​gauge fields suggested possible ways for further development of the principle of the unity of physics and the unification of fundamental physical interactions. One of them is based on the amazing fact that the interaction constants of the electromagnetic, weak and strong interactions become equal to each other at the same energy. This energy was called the energy of unification. At energies above 10n GeV, where n = 14, or at distances r 10n cm, where n = -29, strong and weak interactions are described by a single constant, i.e., they have a common nature. Quarks and leptons are practically indistinguishable here.

In the 70-90s, several competing theories of the Grand Unification were developed. They are all based on the same idea. If the electroweak and strong forces are really just two sides of the grand unified force, then the latter should also have an associated gauge field with some complex symmetry. It (symmetry) must be sufficiently general, capable of covering all gauge symmetries contained in both quantum chromodynamics and the theory of electroweak interaction. Finding such symmetry is the main task towards creating a unified theory of strong and electroweak interactions. There are different approaches that give rise to competing versions of Grand Unification theories.

However, all of these hypothetical versions of the Great Unification have a number of common features:

Firstly, in all hypotheses, quarks and leptons - carriers of the strong and electroweak interactions - are included in a single theoretical scheme. Until now they have been considered as completely different objects.

Secondly, the use of abstract gauge symmetries leads to the discovery of new types of fields that have new properties, for example, the ability to transform quarks into leptons. In the simplest version of the Grand Unified Theory, twenty-four fields are required to transform quarks into leptons. Twelve of the quanta of these fields are already known: a photon, two W particles, a Z particle and eight gluons. The remaining twelve quanta are new superheavy intermediate bosons, united under the common name X and Y - particles (with an electric charge of 1/3 and 4/3). These quanta correspond to fields that maintain broader gauge symmetry and mix quarks with leptons. Consequently, quanta of these fields (i.e. X and Y particles) can transform quarks into leptons (and vice versa).

Based on Grand Unified theories, at least two important patterns are predicted that can and should be tested experimentally: proton instability and the existence of magnetic monopoles. Experimental detection of proton decay and magnetic monopoles could provide a strong argument in favor of Grand Unified theories. Experimental efforts are aimed at testing these predictions. But there is still no firmly established experimental data on this matter. The fact is that Grand Unified theories deal with particle energies above 10n GeV, where n = 14. This is very high energy. It is difficult to say when it will be possible to obtain particles of such high energies in accelerators. This explains, in particular, the difficulty of detecting the X and Y bosons. And therefore, the main area of ​​application and testing of Grand Unified theories is cosmology. Without these theories, it is impossible to describe the early stage of the evolution of the Universe, when the temperature of the primary plasma reached 10n K, where n = 27. It was under such conditions that superheavy particles could be born and annihilated.

Thus, it becomes clear that proving the Grand Unified theory is the main task of physicists today, because this theory will not only help connect disparate fragments of human knowledge into a single picture, but also take a step towards understanding the origin of the Universe.

Bibliography.

School Student's Handbook. 5-11 grades. 2004

Computer encyclopedia of Cyril and Methodius. 2005

I. L. Rosenthal “Elementary particles and the structure of the Universe.” 1984

The problem of elementary particles

At various stages of advancement “into the depths” of a substance, various particles were called elementary (structureless). In search of the basic “building blocks” of the universe, man initially established that all compounds consist of “elementary” molecules. Then it turned out that molecules are built from “elementary” atoms. Centuries later, it was discovered that “elementary” atoms are built from “elementary” nuclei and electrons orbiting around them. Finally, it was discovered that the nuclei themselves are built from protons and neutrons, which until relatively recently were considered elementary particles without an internal structure. After the discovery of the neutron in 1932, it seemed that the basic building blocks from which ordinary matter is constructed were established: protons, neutrons, electrons and photons.

But since 1933, the number of detected elementary particles has been growing rapidly. When their number exceeded a hundred, it became clear that such a huge number of particles could not act as elementary components of matter.

They tried to classify the newly discovered elementary particles, first of all, by mass. Thus, the division of elementary particles into leptons (light) and baryons (heavy) appeared. The electron, positron and neutrino known to us belong to leptons, and the proton and neutron to baryons. There is another group of elementary particles - mesons (intermediate).

Baryons and mesons, as particles participating in the so-called strong interaction (see below), are often combined into a group of hadrons.

The problem of elementary particles, the number of which exceeded three and a half hundred, seemed insoluble for a long time. The breakthrough came when the quark model was proposed in the 60s, which was based on the hypothesis of the existence of new truly elementary particles, which were called quarks. Within the quark model, all baryons are considered as combinations of three quarks, and mesons are considered as combinations of a quark and an antiquark.

Basic characteristics of elementary particles

The main characteristics of elementary particles are the following:

Mass – m

Life time – τ

Electric charge–q

Baryon and lepton numbers (charges)– B, L

Spin – s

One of the main characteristics of subatomic particles is their mass, which simultaneously determines their rest energy. Among particles with zero mass, photons are the best known. The neutrino mass may also be zero. The electron is the lightest of the stable particles with non-zero mass (me =0.911·10-30 kg). The proton has the smallest mass among baryons

(m p =1.672·10 -27 kg). The mass of a neutron is slightly greater than the mass of a proton: mn − mp

2.5me.

Electron and proton are stable particles. The lifetime of a free neutron is about 900 seconds. Most elementary particles are highly unstable, their lifetimes range from a few microseconds to 10-23 s.

Electric charge. The electric charges of all studied elementary particles (except quarks!) are integer multiples of e

1.6·10-19 C (e is the elementary charge, numerically equal to the charge of an electron or proton). In our world, the universal law of conservation of electric charge applies: the total electric charge of an isolated system is conserved.

Baryon (B) and lepton (L) numbers (charges) characterize whether a particle belongs to the class of baryons or leptons. Baryons have no lepton charge ( L =0), for baryon particles B = 1, for antiparticles B = -1. Leptons do not have a baryon charge, and their lepton charge is equal to L = 1 – for particles (electron, neutrino) and accordingly L = -1 – for antiparticles (positron, antineutrino).

The main property of elementary particles is their ability to undergo mutual transformations, which occur only under the condition that all types of charges discussed above are conserved: electric, baryon, lepton (plus the laws of conservation of energy, momentum and angular momentum).

Spin (s) is a special internal characteristic of elementary particles associated with their own (spin) momentum, which is measured in

units of h (Planck's constant) or ћ =									(h crossed out).
In units of ћ, the spin of all elementary particles takes the values ​​or
integers: 0, 1, 2, … or half-integers: 1								, …

Particles with half-integer spin are called fermions, and particles with integer spin are called bosons. Fermions obey Pauli's exclusion principle according to which two identical particles cannot be in the same quantum state.34 All fermions are particles of matter.

Bosons, on the contrary, all tend to get into the same state. All bosons are quanta particles of some field. Of all the bosons, photons are the most common in the Universe.

34 A quantum state is completely characterized by a set of four quantum numbers: three of which are associated with the three-dimensionality of space, and the fourth with spin.

Thus, fermions act as “pure individualists,” while bosons are real “collectivists.”

Fundamental fermions - leptons and quarks

Currently, the truly elementary particles from which all matter in our world is built are considered to be leptons and quarks, whose spin is equal to ½.

The lepton family consists of particles of three generations: to first generation include electron e - and electron neutrinoν e ; second generation– muon μ and muon neutrinoν μ and, finally, third generation–

taon τ - and taon neutrino ν τ:

				μ −
	ν e			νμ		ν τ

The electron, muon and taon appear in pairs only with their neutrinos. Their enormous penetrating power, lack of charge and extremely small, possibly zero mass made them elusive for many years. The most elusive of all elementary particles turned out to be the tau neutrino, discovered only in the summer of 2000.

Neutrinos are so “incorporeal” that they easily penetrate the thickness of the Earth and are able to pass through a layer of lead several light years thick. Meanwhile, neutrinos, along with photons, are the most common particles in our world. If all the matter, including all the galaxies and intergalactic dust, were evenly distributed throughout the entire volume of the Universe, then for every cubic meter of space there would be one proton and one electron. There are billions of times more photons and neutrinos: there are about 500 particles in each cubic centimeter.

Neutrinos were first introduced by Pauli to explain the beta decays of nuclei,

in which the transformation of a proton into a neutron (the so-called β + - decay) and a neutron into a proton occurs:

	→ 0 n						→ 1 p	+− 1 e

Note that the transformation of a neutron into a proton is energetically favorable (since the mass of a proton is less than the mass of a neutron). This is what explains the instability of a free neutron.

If the process of converting a neutron into a proton occurs inside the nucleus,

it is called β - - decay. In this case, the β - particle is an electron.

The process of converting a proton into a neutron requires energy and can only occur inside the nucleus. β + - decay is accompanied by the birth of a particle completely similar to an electron, but with an electric charge of opposite sign, which is called a positron +1 e 0.

In addition to the electron (or positron), β − decays involve another elementary particle, called the neutrino − 0 ν 0 (a particle

accompanying β - − decay).

Antiparticles

The existence of the electron and positron suggests that other elementary particles may have their own “twins.” Indeed, almost every particle has its own antiparticle, the mass of which is strictly equal to the mass of the particle, and the sign of the charge is opposite. There is also a rather rare type of truly neutral particles that do not have twins (photons). In principle, there can exist an antiatom, the nucleus of which consists of antiprotons and antineutrons, and the electrons are replaced by antielectrons (positrons), an antimolecule and, finally, an antimatter, the properties of which will be no different from the properties of ordinary matter.

The most important property of particles and antiparticles is their ability to annihilate. Annihilation of a particle - antiparticle pair (from the Latin annihilatio -

destruction, disappearance) is one of the types of interconversion of elementary particles, accompanied by the release of energy, for example, the transformation of an electron and a positron upon their collision into photons (electromagnetic radiation):

1 e0 + +1 e0 → 2γ

The opposite effect is also possible - the formation of an electron-positron pair when two photons collide. It is clear that the photon energy must be no less than twice the rest energy of the electron E γ > 2m e c 2 (a little more

1MeV).

Our world consists of matter. On Earth, in the Solar System and in the outer space immediately surrounding the Solar System, there is no noticeable amount of antimatter, since due to annihilation reactions the close coexistence of particles and antiparticles is impossible. Those few antiparticles that can be produced in laboratory conditions die sooner or later. The long-term existence of stable antiparticles (for example, antiprotons or positrons) is possible only at a low density of matter - in special accumulators of charged particles or in outer space. Questions about why our world consists of matter, when and why the asymmetry of our Universe arose, are of fundamental importance and continue to attract the attention of theoretical physicists.

The second family of fundamental elementary particles from which hadrons (baryons and mesons) are built are called quarks. There are six varieties of quarks (physicists call them “flavors”), which, like leptons, group in pairs and form three generations. First generation– u and d quarks (up - top and down

Lower); second generation - s and c quarks (strange - strange and charm -

enchanted) and, finally, the third generation - b and t quarks (beauty - beautiful and true - true ; sometimes they are called bottom and top ). Last sixth t-quark was discovered relatively recently (in 1995).

Quarks are fermions (their spin is ½, like leptons). In this case, two internal quantum states with vector projections are possible -

back: +1/2 and –1/2

The baryon number for quarks is equal to one third B = 1/3, for antiquarks

− B = –1/3. Each quark has another characteristic, which physicists call flavor (strangeness, charm, etc.).

The most surprising thing is that quarks have a fractional electric charge, the value of which is either 2/3 of the elementary charge (the quark charge is positive) or 1/3 of the electron charge (the charge sign is negative).

All baryons are combinations of three quarks. Nucleons - the fundamental basis of atomic nuclei, are the lightest baryons and consist of first-generation quarks. A proton is made up of two u-quarks and one d-quark, a neutron from two d-quarks and one u-quark:

It is easy to check that the proton charge turns out to be equal to unity (2/3+2/3–1/3 = +1), and the neutron charge is zero (2/3 – 1/3 – 1/3 = 0).

The neutron is heavier than the proton because the d quark is heavier than the u quark.

The processes of β + – and β – – decays as the interconversion of quarks (u d) receive a new explanation.

Mesons are produced from the combination of a quark-antiquark pair. It's clear that
the baryon number of mesons is zero,						spin is equal to	zero or one.
Combinations of three antiquarks form antibaryons (antiprotons,
antineutrons, etc.).
Table 1 presents all fundamental fermions -
structural units of the structure of matter.
			Table No. 1
		Fundamental fermions
Foundation-
	Generations						III Electric
fermions			generation			generation	generation
	charged
			electron					−1
						νμ	ντ
	neutrino		electronic
					charmed		true
							Beautiful
All the diversity of hadrons arises due to various combinations
given						aromas.

correspond to bound states constructed only from u- and d-quarks. If in a bound state, along with u - and d -quarks, there is, for example, an s - or c -quark, then the corresponding hadron is called strange or

charmed.

The fact that all known baryons and mesons could be obtained from various combinations of quarks symbolized the main triumph of quark theory. However, all efforts to detect single quarks were in vain. A paradoxical situation has arisen. Quarks undoubtedly exist inside hadrons. This is evidenced not only by the considered quark systematics of hadrons, but also by the direct “transmission” of nucleons by fast electrons. In this experiment (essentially completely similar to Rutherford’s experiment), it was discovered that inside hadrons, electrons are scattered on point particles with charges equal to –1/3 and +2/3 and spin equal to ½, that is, direct physical evidence of the existence of quarks inside hadrons. But it is impossible to remove quarks from hadrons. This phenomenon is called "confinement"

(confinement - captivity, English).

Fundamental Interactions

The next fundamental question that science must answer to explain the structure of matter is related to the nature and nature of the interaction between particles, which under certain conditions leads to the formation of bound states. What makes quarks combine into nucleons, nucleons into nuclei, nuclei and electrons into atoms, atoms into molecules? Why are there accumulations of matter in the form of planets, stars, and galaxies in the Universe? What is the nature of the forces that cause all the changes that occur in our material world?

It turns out that everything that happens in nature can be reduced to just

four fundamental interactions

The role of fundamental interactions in nature

Gravitational interaction is the weakest and at the same time the most universal. Gravitational interaction acts between any objects that have mass or energy. It is gravity that prevents the Universe from falling apart, collecting matter into planets and stars, keeping planets in orbit, “connecting” stars into galaxies. In general, on an astronomical scale, gravitational interaction plays a decisive role. In the microcosm, gravity can be neglected compared to other more intense interactions.

Electromagnetic interaction common to all particles

having an electric charge. Like gravitational, electromagnetic interaction is long-range, and the law that determines the force acting between point charges at rest is similar to the law of gravity - this is Coulomb’s law, known from school:

		m 1 m 2			q 1 q 2

However, unlike gravity, which is always an attraction, electrical attraction exists only between charges of opposite signs, while charges of the same sign repel. It is thanks to electromagnetic interaction that the formation of atoms and molecules is possible. Intermolecular forces that determine the properties of various states of aggregation of a substance are also of an electrical nature. Most observable physical forces (elasticity, friction, etc.) actually come down to it; it is what underlies the chemical transformations of substances and all observable electrical, magnetic and optical phenomena.

Strong and weak interactions appear only in the microcosm, at the subnuclear level.

Strong interaction inherent in quarks and formations of quarks - hadrons. The main function of the strong interaction is to combine quarks (and antiquarks) into hadrons. The nuclear forces that unite nucleons into nuclei are specific echoes of the strong interaction (often called the residual strong interaction).

Weak interaction inherent in all fundamental fermions. For neutrinos, this is the only interaction in which they participate. Unlike the strong interaction, the function of the weak interaction is to change the nature (flavor) of particles, that is, to transform one quark into another (the same applies to leptons).

In the absence of the weak interaction, not only the proton and electron would be stable, but also muons, π - mesons, strange and charmed particles that decay as a result of the weak interaction. If we could “turn off” the weak interaction, the Sun would go out,

since the process of converting a proton into a neutron (β decay), as a result of which four protons turn into 2 He4, two positrons and two neutrinos (the so-called hydrogen cycle, which serves as the main source of energy for the Sun and most stars.) would be impossible.

Characteristics of fundamental interactions

The intensity of interactions can be judged by the speed of the processes they cause. Usually compared to each other process speed at an energy of 1 GeV, characteristic of particle physics. At such energies, the process caused by the strong interaction

occurs in a time of 10-24 s, the electromagnetic process in a time of 10-21 s, the characteristic time of processes occurring due to weak interaction is much longer: 10-10 s.