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 a lot of such particles, much more than atoms of chemical elements.
Particles 10 times heavier than a proton and about the same mass as the boron nucleus have recently been discovered. Desperate to reveal any hierarchy in the growing set of equally elementary objects, some physicists put forward the idea of bootstrap lacing, or nuclear democracy, according to which each elementary particle consists of all other particles more precisely, 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 of the 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 various ways. The definition of structure elements becomes very ambiguous.
Since one and the same particle can be composed in various ways from other particles. Moreover, it remains unclear whether it is possible at all along this path to formulate an exact closed system of equations that determines various properties, including the structure of elementary particles. Theorists have analyzed only very crude bootstrap models that take into account the relationship of only two or three kinds of particles, and although in some cases they have obtained promising qualitative results, attempts to refine them immediately run into enormous difficulties.
The idea of a bootstrap cannot be considered a satisfactory solution to the problem of the simplest elements. Much more fruitful turned out to be 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. The guiding principle is the identification of 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. The discovery of the so-called unitary symmetry, which made it possible to combine isotopic multiplets of ordinary and strange particles into single octets and decaplets, was of great importance. Taking into account the spins made it possible to construct even more complex families of particles, unitary multiplets of mesons combined into a family consisting of 35 particles 35 - a lash, and the octet and decaplet of baryons into a family of 56 elements 56 - a lash. Further development of the systematics of particles is associated with the idea of quarks.
It turned out that individual unitary multiplets are not completely isolated from each other, but are linked by strict symmetry rules. And the most striking thing was that these rules predicted the existence of particles with fractional electric quark charges. At the modern level of development of science, these particles can really be considered the most elementary, because everything else can be built from them, interacting particles sometimes by simple addition, like atomic nuclei from protons and neutrons, and sometimes considering them as excited states of already constructed particles and in at the same time, the 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 single out any more elementary building elements.
Quarks can be considered as the next, deeper, superelementary level of organization of matter from the point of view of the magnitude of the mass defect, that is, the density from packing inside protons, mesons and other less elementary objects.
From the standpoint of the theory of quarks, the structural level of elementary particles is the region of objects consisting of quarks and antiquarks and characterized by a large mass defect with respect to any of their decays and virtual dissociation.
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 by a fractional electric charge, but also by a fractional baryon number. Among other elementary particles, it looks like a kind of centaur in its properties, it is simultaneously a meson and a baryon. Initially, it was believed that a quark has three states, two of them differ only in the magnitude of the electric charge, and in the third state, the quark manifests itself as a strange particle.
However, after the discovery of families of charmed charmed particles, a fourth charm had to be added to the three quark states. In fact big world At the 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 stuck together quark and antiquark. In this case, it is necessary to assume that the quark and antiquark have one more, fifth state.
For the quantum number that characterizes this state, there is not even a generally accepted name, most often it is called the charm of a quark or the corresponding English term beauty. Five quantum degrees of freedom of a quark is usually called its flavor, some authors prefer to talk about five degrees of taste of a quark. But even these do not exhaust the list of quark properties. Analysis of the experimental data led to the conclusion that each of the five aromas of quark tastes has three colors, that is, each of the five quark states is split into three independent states characterized by the value of the specific quantum number of the color.
The color of a quark changes when it emits or absorbs a gluon of an intermediate field quantum that glues quarks and antiquarks into mesons and baryons. We can say that the gluon field is a color field, its quanta transfer color. The term gluons comes from the English word glue glue. Nowadays, the idea of super-elementary particles of quarks literally permeates the physics of energy.
With their help, so much experimental data is explained that it is simply impossible to get around physics without these amazing particles, just like, for example, a chemist 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 striking mystery. 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 remain, although probable, but still hypothetical objects. Indirect experiments are convincing that quarks and gluons are physical objects, and not just a convenient phenomenological way of describing in our usual corpuscular language some still incomprehensible aspects of the structure of elementary particles. First of all, these are experiments on probing protons into a neutron with the help of very fast electrons and neutrinos, when the incident particle scatters bounces off, colliding with one of the quarks inside the target particle. Taking into account quarks, the list of strongly interacting superelementary particles will be reduced to three particles - a quark, an antiquark and a gluon that binds them.
To them should be added about a dozen more of the simplest particles of other types, the structure of which has not yet manifested itself in the experiment, the quantum of the electromagnetic field, the photon, which is 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 such effects as scattering of muonic neutrinos by electrons. A whole group of elementary particles with a lifetime exceeding the lifetime of resonances by a factor of a thousand has been discovered, starting with the J-meson. In fact, it is already now necessary to include these particles in the table of relatively stable elementary particles.
Significant advances in the theory of elementary particles. The unified theory of weak and electromagnetic interactions has received solid experimental confirmation, although it still cannot be reckoned with certainty. The quark model of the structure of hadrons receives more and more experimental confirmation. After many years of stagnation, great progress has been made in the theory of strong interactions, which are now regarded as inter-quark interactions.
It is very likely that leptons and quarks are truly elementary particles, indivisible even further. All the vast majority of hadrons are built from quarks. The model of four color 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 a stationary target is bombarded with high-energy protons, superheavy neutral mesons, called upsilons with a mass of about 9.4 GeV, have been discovered. Three modifications of these mesons with similar masses were found.
To include upsilons in the quark model, one must assume that there are quarks more massive than the c-quark. To preserve the quark-lepton symmetry requires the introduction of two new quarks corresponding to the pair -lepton, -neutrino. These quarks have already received the name top top in English and bottom bottom. So, with an increase in the energy of the colliding particles, the birth of new more and more heavier particles is revealed.
This complicates the already complicated picture of the world of elementary particles. New problems are emerging, although many old problems remain unresolved. Probably, the main unsolved problem should be considered the problem of quarks, whether they can be free or whether their trapping inside hadrons is absolute. If, in principle, quarks cannot be isolated and detected in a free state, then how to make sure that they exist with certainty. ...
Undoubtedly, the 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 -
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William Hilbert formulated a postulate about 400 years ago, which 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 not agree 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 is 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 (a burst of a magnetic field), devoid of an electric component and having a 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 of it suggest that the magnetic γ-quantum can be identified with the neutrino. On this basis, it is possible to take a fresh look at the nature of the π-meson, μ-meson and λ-hyperon by calculating their masses and magnetic moment.
1. The main postulate of 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 composed of quarks with an integer charge.
2.3. Physical properties of the neutron.
2.4. The structure of the neutron.
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 nuclei.
3.3.1. Nucleus 3 2 He.
3.3.2. The 4 2 He nucleus.
3.3.3. The nucleus is 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 sciences in the 21st century, it may seem that medieval science was concentrated in theology, astrology and alchemy. But this is absolutely not the case. The Middle Ages was the time when the foundations of modern science were developed.
The medieval scientist William Hilbert (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-scientific research *.
* It can be assumed that the idea of this principle, as they say, was in the air among the educated people of that time. But he found his own formulation, which has come down to us, this principle thanks to W. Hilbert.
Hilbert's principle is simply stated:
All theoretical constructions 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 number of scientific constructions were created, which were accepted by the scientific community and are still dominant in their fields of knowledge, but at the same time they do not satisfy the Hilbert principle.
1.1. Hilbert's postulate and modern physics
It should be emphasized that in 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 wrong.
Let us consider some problems of the microworld, in the solution of which the Hilbert principle was violated.
2. Proton and neutron
2.1. Proton and neutron in the Gell-Mann quark model
One gets the impression that the specialists in elementary particle physics first proceeded from the assumption that when the world was created, each elementary particle was individually selected for the appropriate parameters: charge, spin, mass, magnetic moment, etc.
Gell-Mann simplified this work somewhat. He developed a rule according to which a 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. Gell-Mann quark structure of the proton and neutron. Quark charges 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 claim to predict the masses and magnetic moments of the proton and neutron
The quark Gell-Mann model assumes that the quarks, of which all elementary particles (except for the lightest) are composed, must have a fractional (equal to 1/3 e or 2/3 e) electric charge.
In the 1960s, 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 forbids them to manifest 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 the scattering of particles at high energies, for example, the formation of jets or the feature of the scattering of high-energy particles without destruction. However, this does not seem to be enough to recognize the existence of quarks with fractional charges.
2.2. Model of a proton composed of quarks with an integer charge
Let's set ourselves the goal of constructing a model of a 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... Suppose that these quarks do not have their own spin, and their quantum motion is expressed by their rotation around a common center around a circle of radius R.
Rice. 2.
Let the value of the radius R is determined by the fact that on the circumference 2π R the length of the de Broglie quark wave λ D:
The generalized angular momentum (spin) of the system will be composed of two terms: from mechanical moment rotation of all three quarks 3 p q × R and angular momentum of the magnetic field created by a quark with an uncompensated charge \ (\ frac (e) (c) (\ bf (A)) \):
and the magnetic moment of the circular current
here β = v/c.
Based on the fact that the magnitude of the proton spin is ħ / 2, we have
The total mass of three quarks
Taking into account the magnitude of the quark mass (8), the magnetic moment created by it is obtained 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 consists of a different set of quarks than the proton. In the 30s of the last century, theoretical physicists came to the conclusion about the elementary nature of the neutron, not relying on measurement data, which were not available at that time.
To explain the measurement data of the parameters of the neutron - the magnetic moment of the neutron, the mass and energy of its decay - let us 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 revolves at a very small distance from it. Near a proton, the motion of an electron must be relativistic. However, the peculiarity of the stable orbit formed in this case is that during its calculation, all relativistic corrections cancel each other out and completely drop out.
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 in physics, the question of whether it should be considered an elementary particle was discussed. There were no experimental data that could help solve this problem, and soon the opinion was formed that the neutron, like the proton, is an elementary particle. However, the fact that a neutron is unstable and decays into a proton and an electron (+ antineutrino) gives grounds to class it as a non-elementary compound particle.
Consider a compound particle in which around a proton with a velocity v → c a particle with a rest mass rotates m e and charge - e... (Previously, a similar approach was considered in works and).
Let us choose a cylindrical coordinate system in which the axis z coincides with the direction of the magnetic moment of the proton
There must be a force of Coulomb attraction between a positively charged proton and a negatively charged electron (, §24):
which manifests itself in the Lorentz force:
and the force created by the magnetic field of the ring tending to break it
As a result, this equation of equilibrium 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- constant of fine structure,
r c = ħ / m e c Is the 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 is in good agreement with the measured value of the magnetic moment of the neutron (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 exactly agrees with the experimentally determined limit of the spectrum of decay electrons, equal to 782 keV.
2.5. Discussion
In the model of the proton considered above, composed of quarks with integer charges, there is no question of the observability of quarks in a free state. However, a lot remains unclear.
It is not clear where the magnetic moment of the positron, which 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 make them unite into a completely stable particle - a proton, the decays of which are not observed in nature.
The obtained agreement of the estimates with the data of measurements of the properties of the neutron suggests that it is not an elementary particle. It should be considered as a kind of relativistic analogue of Bohr's hydrogen atom. With the difference that in a Bohr atom a nonrelativistic electron is held on the shell by Coulomb forces, and in a neutron a relativistic electron is held mainly due to magnetic interaction. In accordance with Hilbert's postulate, the confirmation by experiment of the above electromagnetic model of the neutron seems to be a necessary and completely sufficient argument for its reliability.
Nevertheless, in order to understand the model, it is important to use the generally accepted theoretical apparatus when constructing it. It should be noted that for scientists accustomed to the language of relativistic quantum physics, the technique used in the above estimates does not facilitate the perception of the results obtained at a cursory glance. It is generally accepted that for reliability, taking into account the influence of relativism on the behavior of an electron in a Coulomb field should be carried out within the framework of Dirac's theory. However, in the specific case of calculating the neutron mass, its magnetic moment and decay energy, this is not necessary, since the electron spin in the state under consideration is zero and all relativistic effects described by terms with the coefficients \ ((\ left ((1 - \ frac ((( v ^ 2))) (((c ^ 2)))) \ right) ^ (- 1/2)) \), cancel each other out and completely drop out. 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, since coefficient \ ((\ left ((1 - \ frac (((v ^ 2))) (((c ^ 2)))) \ right) ^ (- 1/2)) \) into definition R 0 is not included. This makes it possible to calculate the mass of a neutron, its magnetic moment and decay energy, simply by finding the equilibrium parameters of the system from the condition of the balance of forces, as is customary for nonrelativistic objects. The situation is different with the estimate of the neutron lifetime. This parameter is likely to be influenced by relativism. Without taking it into account, it is not possible to correctly estimate the neutron lifetime, even in 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 in the event that the state of a molecular ion is described by a double-well potential (Fig. 3). This exchange is a quantum mechanical effect and does not exist in its classical counterpart. (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 an 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 either be in the right or left side of the well. In an unperturbed state, its energy is E 0. Tunneling from one state to another leads to the 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, considered above, allows a new look at the mechanism of interaction of a neutron with a proton. Neutron - i.e. a proton surrounded by a relativistic electron cloud - and a free proton together make up an object like 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 a mass of about 2.57 m e.
The application of the results of quantum mechanical calculations by Heitler - London to this case makes it possible to estimate the binding energy of a deuteron with an accuracy of about the same as in the case of a molecular hydrogen ion. The estimate predicts a binding energy of approximately 2.13 · 10 –6 erg, while measurements give
3.3. Light nuclei
3.3.1. Nucleus 3 2 He
Fig. 4, which schematically shows the energy bonds in the 3 2 He nucleus, it can be seen 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 three times the binding energy of the deuteron:
The mass defect of this nucleus
Evaluation Consent 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 energy ties in the 4 2 He nucleus shown in Fig. 4, it can be seen 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
Such agreement of these values can be considered quite satisfactory.
3.3.3. Nucleus 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 next shell:
This assumption is possible if the exchange of an electron between protons of different shells is difficult.
At the same time, the mass defect of this nucleus
and the associated binding energy
which really confirms the weak coupling between protons on different shells.
It should be noted that the situation with the rest of the light nuclei is not so simple. Kernel 3 1 T consists of three protons and two electrons that communicate between them. The jump of two electrons in such a system should obey Pauli's 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 scheme E Li7 ≈ E He4 + E T, but this view 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 of the calculated binding energy for some light nuclei with the measurement data suggests that nuclear forces (at least in the case of these nuclei) have the exchange character described above.
Apparently I.E. Tamm back in the 30s of the last century. However, later in nuclear physics, the predominant model became the exchange of π-mesons, and then gluons. The reason for this is clear. To explain the magnitude and radius of action of nuclear forces, a particle with a small intrinsic wavelength is needed. A nonrelativistic electron is not suitable for this. However, on the other hand, the models of π-meson or gluon exchange have not been productive either. These models could not give a sufficiently accurate quantitative explanation of the binding energy of even light nuclei. Therefore, the above simple and consistent with measurements estimate of this energy is unequivocal proof 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 shown earlier that there are two possibilities within the framework of the standard Maxwellian theory of the electromagnetic field. Using different methods of excitation, it is possible to excite in empty space (ether) either a transverse electromagnetic wave (photon) or a magnetic quantum (magnetic soliton), i.e. a wave devoid of an electrical component. To generate electromagnetic waves in a vacuum, an oscillating electric or magnetic dipole must be used.
According to Maxwell's equations, the quantity electric field carried by a photon is proportional to the second time derivative of the time-varying magnetic moment that the photon generates. If the time dependence of the magnetic moment is described by a perfectly sharp Heaviside step function, then the first derivative of this step is the δ-function, and the second derivative is zero. Therefore, with the leading edge of the step lasting about 10–23 seconds (this is the estimate of the time of the 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 details in) ...
A characteristic feature of a magnetic soliton is that, being circularly polarized, it must have a 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, at the birth of a magnetic moment, an antineutrino arises, and when it disappears, a neutrino.
Thus, in the process of successive transformation of the π - meson, first into the μ - meson, and then into the electron, three such magnetic γ quanta arise (Fig. 5).
Rice. 5. Scheme of the production of three magnetic solitons (neutrinos) during the decay of the π - meson. π - -meson has no magnetic moment. When decaying, it turns into a μ - meson carrying a magnetic moment. This process should be accompanied by the emission of a magnetic γ-quantum (antineutrino emission). When the 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 equal to zero, do not have magnetic dipoles. At the moment of the transformation of a π - -meson into a muon (μ-meson), a magnetic moment appears abruptly, which is accompanied by the emission of a muonic antineutrino \ ((\ widetilde \ nu _ \ mu) \). When the muon decays, the radiation of the muon neutrino 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 momentum of a particle,
n= 1, 2, 3 ... is an integer.
The invariant angular momentum (spin) of such a particle
we get
This mass is very close to the mass of the π-meson (46), which has a spin of zero:
This mass 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, proceeding only from 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 quark charges, within the framework of which such estimates cannot be obtained. This model in its modern form demonstrates the possibility of classifying particles, but it does not prove that such a classification is the only possible and correct one.
It is important to note here that to describe the proton-neutron interaction (in light nuclei) there is no need to invoke the gluon model, as well as to use the theory of strong and weak interactions.
Indeed, the exchange of a relativistic electron between protons in a deuteron and, like the exchange of a nonrelativistic electron in a molecular hydrogen ion, is a quantum mechanical phenomenon and there is no reason to ascribe to this exchange effect in the case of a deuteron the role of the fundamental interaction of Nature.
Emission of neutrinos occurs in the process of β-decay (or K-capture). Nuclear decay processes, both α and β, do not require the introduction of any new special fundamental natural interaction. But β-decay has an essential feature: in β-decay, extremely a short time the magnetic moment of a free electron appears (or disappears during K-capture). This produces a magnetic impact on the ether and leads to the emission of a magnetic γ-quantum, i.e. neutrino. This phenomenon has a purely electromagnetic character, and for its description it is not necessary 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. Obviously, to calculate the 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 electromagnetic description of some particles makes the question of the correctness of the existing description of many other, more complex objects of the microworld urgent.
Obviously, in accordance with the main postulate of natural sciences by W. Hilbert, 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:
- Gilbert W. About magnet, magnetic bodies and a big magnet - the Earth. Moscow: Publishing House of the Academy of Sciences of the USSR, 1956. , 2016.
At the first stage, the desire to somehow limit the number of elementary constituents of matter led to a discussion of theoretical schemes in which only a fraction of the known hadrons were considered fundamental particles, which were considered as bound states consisting of fundamental hadrons. However, later it turned out that these schemes can describe the properties of all known particles.
With the increase in the number of discovered hadrons, the difficulties faced by such schemes became more complicated and it became more and more obvious that hadrons cannot be elementary formations, elementary particles, if they exist, must be objects of some other nature.
Integer-spin hadrons are called mesonic ones, since the first mesons discovered (seventh, K) had a mass intermediate between the mass of an electron and a proton. Due to their significant mass, hadrons with pivcylem spin are called baryonic hadrons. These include nucleons, hyperons and some other particles.
Knowledge of the characteristics of hadrons makes it possible to reliably classify them, that is, to single out groups with the same or similar properties. We have mentioned some of these rather broad groups. It turns out that it is possible to distinguish other groups of hadrons that are close to each other in some ways. Modern research is aimed at searching for fundamental particles, from which it is possible to create all highly intermittent particles, i.e. hadrons. These fundamental particles have the following requirements: they must be baryons and antibaryons - particles with respectively positive and negative baryon charges. their combination contributes to the formation of a baryon charge of any hadrons. The baryon charge of mesons is zero, so they are obtained by combining baryons with an antibaryon. Fundamental particles must have the minimum pivcyle value of the usual spin, so that particles with any integers and pivcyle spins can be constructed from them. Among them, there must be a Baryon with a strangeness equal to one to control strange particles. It is also important that the mass of fundamental particles is not very different, which may indicate the same values of the strong interaction that exists between them. Another requirement is related to the isotopic spin of fundamental particles. To be able to get any isotopic multiplet, we must have at least an isotopic singlet and an isotopic doublet at our disposal.
S. Sakata, guided by these requirements, took three baryons as fundamental particles - a proton, a neutron and a -hyperon (p, n, X) and their antiparticles (p, n, X). Sakata's scheme satisfactorily describes mesonic hadrons, but turns out to be unsuitable for baryonic hadrons. To eliminate the shortcomings of Sakata's scheme, the octet formalism of M. Gell-Mann and Yu. Neumann was applied. The authors of the octet formalism proposed to expand Sakata's scheme by choosing eight baryons instead of three as fundamental particles.
It turned out to be possible to extend the new scheme to baryonic hadrons. Based on the proposed scheme, Gell-Mann predicted the existence of an unknown at that time and ~ -hyperon. At the same time, using the octet scheme, they determined not only all the quantum numbers of the provided hyperons, but also its mass. The predicted value of the mass coincided with the experimental value when the ^ "-hyperon was discovered at Brookhaven in a two-meter hydrogen bubble chamber irradiated with K-mesons.
In the first form of this model, three types of quarks were proposed, designated by the letters u, d9 s, which come from the English words up (up), down (down), strange (strange). The strangeness was carried by the s quark, so all strange particles included at least one s quark, or s antiquark. In the quark model, the mass distribution between hadrons reflects the mass distribution between quarks. So, since the s-quark is much more massive than other quarks, the mass of strange hadrons is much larger than the mass of hadrons.
Later the system of quarks was expanded, quarks were additionally introduced: "charmed" (c), "attractive" (b) and "truthful" (t). The properties that are attributed to quarks are given in Table. 18.3. The reason for the increase in the number of quarks was that bound states of three quarks like uu (D +), ddd (D), sss (? ~) Contradict Pauli's principle. From table. 18.3 it can be seen that all quantum numbers of quarks in these formations are the same. Since quarks have spin pivots and, therefore, can be described by Fermi statistics, in one system there can be no not only three, but even two quarks with the same set of quantum numbers. Proceeding from some considerations, in particular to eliminate the contradiction with Pauli's principle, the concept of "color" of a quark was introduced. The idea arose that each quark can exist in three "colored" forms: red, green, blue (note that a mixture of these colors gives a "zero" white color). Then it can be argued that the quarks that form, for example, Q ~ -hyperon have different colors, so the Pauli principle is not violated.
The combination of "colors" of quarks in the case of hadrons should be such that, on the whole, the "color" of the hadronic was zero (ie, the hadron should be "colorless"). So, the composition of a proton includes quarks and (red), and (green) and d (blue). The result is zero (white) "color".
Antiquarks are considered to be painted in additional “colors” (“anticolors”), giving zero “color” together with the “color”. Therefore, mesons consisting of a quark and an antiquark also have zero "color". Basically, the "color" of a quark (like an electric charge) conveys a difference in properties that determines the attraction and repulsion of quarks. By analogy with the quanta of the fields of various interactions (photons in electromagnetic interaction, p-mesons in strong interaction, etc.), particles-carriers of interactions between quarks have been introduced. These particles were called gluons (from the English. Glue - glue). They transfer "color" from one quark to another, with the result that the quarks are held together.
Another characteristic feature of quarks is their electrical charge. Quarks d, s, b have a charge of -1 / 3, while the charge of quarks c, c, t is +2 / 3. Antiquarks d, s, b, etc. have electric charges of opposite sign, therefore, the electric charge antiquark d is equal to +1 / 3, antiquark is equal to -2 / 3, etc. antiquarks are also characterized by opposite colors: anti-worm, anti-green and anti-blue. In the formation of hadrons, quarks can be combined in two ways: either three quarks combine with one quark of each "color", or a quark of a certain "color" attaches an antiquark to itself with a corresponding "antiquark". These combinations are called "colorless", and they, besides this, have another important feature. In all possible combinations, the fractional electric charges of the quarks add up so that they give an integer total charge; no other combinations (except those formed by addition of already allowed combinations) have this property. The quark composition of the proton uud, giving a total electric charge of 2/3 + 2 / 3-1 / 3 or +1. The neutron is composed of uud quarks with a charge of 2 / 3-1 / 3-1 / 3, resulting in zero. A positive pion contains a quark and and an antiquark J, their charges +2 / 3 and +1 / 3 add up to +1.
It is customary to divide leptons and quarks into three generations. Each generation consists of a charged lepton, its corresponding neutrino and two quarks, one of which has a charge of -1 / 3, and the second +2 / 3. The first generation consists of an electron, an electron neutrino, and diu quarks. Since quarks exist in three "colors", this generation contains eight particles, representatives of other generations are observed practically only in laboratory experiments with accelerated particles. In a unified theory, these three generations are described independently, but in a similar way.
In fig. 18.2 depicts three generations of leptons and quarks: charges in target leptons, in quarks - fractional. Leptons exist in a free form, and quarks are only components of more complex particles - hadrons. An ordinary substance contains particles only from the first generation. The development of elementary particle physics allows for a complex structure of quarks and leptons, i.e. they, in turn, are composed of sub-quarks. The subquark hypothesis is being discussed by many scientists, although no one has yet been able to get around the difficulties that are encountered along the way, apparently because they are of a fundamental nature.
Now the "interior" of the particles has been studied to a size of the order of 10 ~ 18 m, but no subquarks have been found. It is quite likely that the fundamental physical laws known today cease to operate at distances less than 10 ~ 18 m, and the discovery of subquarks, if it takes place, will lead to a change in the basic concepts of the laws of nature.
We have considered some of the problems of particle physics, which studies the properties of matter. It is difficult to predict the course of development of this branch of physics. However, experimental results in the field of elementary particle physics are a reliable basis for its development in the future.
All currently known elementary particles can be divided into groups according to their general properties and relation to interaction. There are four such interactions in nature: strong, electromagnetic, weak and gravitational.
Strong the interaction has the highest intensity compared to other interactions. It determines the connection between protons and neutrons in the nuclei of atoms (by exchanging virtual n-mesons), which ensures the exceptional strength of these formations.
Electromagnetic interaction characterizes less intense processes. It determines the connection of atomic electrons with nuclei, the connection of atoms in molecules, as well as the interaction of matter with electromagnetic fields.
Weak interaction characterizes the processes associated with the particles themselves, in particular with (β-decay, as well as decays of μ, π, K-mesons and hyperons. It turned out that the weak interaction is universal, all particles participate in it. The lifetime of most of such particles lies in the range of 10 -8 - 10 -10 s, while the typical time of strong interactions is 10 -23 -10 -24 s. An illustration of such an interaction is the fact that neutrinos capable of only weak matter, the distance is ~ 10 14 km.
Gravitational the interaction, so well known for its macroscopic manifestations, in the case of elementary particles, gives extremely insignificant effects due to the small value of their masses. However, these effects significantly increase in the microworld at distances of the order of 10 -33 cm, since the mass of the generated particles increases. These interactions play a dominant role in the megaworld.
Comparison of these four interactions by dimensionless parameters associated with the squares of the corresponding interaction constants gives the following ratios for the strong, electromagnetic, weak and gravitational: 1:10 -3: 10 -10: 10 -38. Generally speaking, the intensity of various processes depends in different ways on energy; therefore, with an increase in the energy of interacting particles, the relative role of various interactions changes.
Depending on the participation in certain types of interactions, all particles, as we have already indicated, can be divided into four groups.
I group: е, μ, τ, ν е, ν μ, ν τ - leptons participate in weak and electromagnetic interactions; II group are strongly interacting particles (there are now more than 300 of them), called hadrons(they also participate in weak and electromagnetic interactions).
The study of hadrons led to the conclusion that there is something in common in their structure. In 1964 M. Gell-Mann and J. Zweig put forward a hypothesis that the structure of all hadrons includes objects exotic in their characteristics, called quarks... It was assumed that there are three types of quarks u, d, s, whose charges are fractional е u = + 2/3, e d = e s = - 1/3 of the electron charge, and masses m u = m d ~ 300 MeV, m s ~ 450 MeV. In the future, as the logic of the development of the theory demanded, to describe the weak interactions of hadrons (weak decays), it was necessary to introduce quarks of another type, the so-called c-quarks with a charge e c = e u = + 2 / s of the electron charge. This quark is characterized by a new quantum number called charm.
In November 1974, a new particle J / ψ with unusual properties was discovered (the mass of 3.1 GeV is about three times the mass of a proton), the lifetime is ~ 10 -20 s (that is, 1000 times longer than any known previously particles with such a large mass). It splits into pairs e + + e - or μ + + μ -. Soon a particle was also discovered, called ψ "(mass 3.7 GeV).
Experiments have shown that the particles J / ψ, ψ "belong to a whole family of mesons, which is in good agreement with the spectrum of charmonium with an effective mass corresponding to the c-quark mass predicted by the theory (m с ≈ 1.6 GeV). was to discover hadrons with obvious “charm.” At present, phenomena have been discovered that indicate the creation of charmed particles.
Physicists believe that the existence of the c-quark is experimentally confirmed. But since the existence of c-quarks was based on the assumption of the existence of light quarks - u, d, s, the discovery of charmed charmed hadrons is of fundamental importance for confirming the truth of the entire quark hypothesis.
Theoretical physicists came to the conclusion that quarks of each type should be in one of three states, which are now usually characterized by three flowers(for example, yellow, blue, red); they assume that the strong interaction of quarks is the interaction of their color with a new field, the so-called. gluonic (from the English glue - glue, because this field, as it were, "glues" the quarks in the hadron). The quanta of the gluon field - gluons- do not participate in electromagnetic and weak interactions. They not only change the color state of the quark, but they themselves bear the color and interact with the gluon field. All this gave rise, by analogy with quantum electrodynamics, a new branch of physics - the so-called quantum chromodynamics.
It is important to emphasize that quarks and gluons are not observed in a free state, they do not "fly out" from hadrons.
There are special studies that prove the fundamental impossibility of the existence of quarks in a free state.
Physicists have long been trying to create a consistent theory of weak interactions. In 1967 S. Weinberg and A. Salam proposed a variant of such a theory - they built a model based on the use of general principles symmetry. This theory predicted the existence of previously unknown particles - quanta of special vector fields responsible for the transfer of both weak and electromagnetic interactions.
Two of these W ± particles must have charges and can be actually observable, since, in their opinion, it is the exchange of charged W ± mesons that generates the weak interaction of the so-called charged currents. As for the two neutral particles W °, B ° -quants of neutron fields, then quanta of any of their linear combinations can be physically observable:
where Θ W, is the so-called Weinberg angle.
It was shown that one of their combinations - the so-called field A - is identified with the electromagnetic field, and the exchange of neutral Z ° mesons gives rise to a new type of weak interactions - the so-called neutral currents, which were discovered in 1973, they became the first confirmation of the relative truth of the Weinberg-Salam model. At present, W ± and Z ° -particles are discovered.
It is necessary to pay attention to the discovery of new leptons. This is an extremely rare event. Suffice it to recall that the electron (e) was discovered in 1897, and the muon (μ) in 1936-1938. 1975-1976 data appeared in favor of the existence of τ ±, the so-called heavy lepton with a mass of 1.8 GeV (2 Mp). The study of the τ-lepton provides another argument in favor of the three states of quarks. An assumption was made about the existence of a new lepton (v τ - a new neutrino), the τ-lepton has a new lepton quantum number, which was named sevolepton(from the English sequential - sequential).
Further research led to the conclusion that in order to restore symmetry, the number of quarks should be increased. Four was no longer enough to describe the objects of the microworld, it was necessary to introduce two more quarks. The fact is that in May - June 1977, L. Lederman's group obtained important results, namely, a new family of heavy particles with masses of ~ 10 GeV was discovered.
The discovery of these particles (they were called γ-mesons) gave rise to the need for the existence of an even heavier "b" quark with an effective mass m b ~ 5 GeV with a new quantum number called "beauty".
The new γ-mesons are particles with hidden charm. Thus, the study of hadrons and leptons has enriched science with knowledge about new objects, about their quantitative and qualitative characteristics, about their interactions. All this testifies to the onset of a new era in the study of the inexhaustible properties of micro-objects, which, together with various fields, constitute a fragment of the integral material world.
Now there is hope for the creation of a unified theory of interaction. At one time A. Einstein tried to create such a field theory. W. Heisenberg also made a lot of effort to build a unified (so-called spinor) theory of "pra-matter". Now we have witnessed the formation of another version of the unified theory of interaction, called the Great Unification.
Already managed to create a single electroweak interaction, encouraging results have been obtained in combining strong and electroweak interactions; and strong and weak interactions are in themselves a manifestation of it. Outside the unification, there is still gravitational interaction, but there are already approaches to including it (supersymmetry) in the unified theory of interaction.
The modern development of the physics of elementary particles has made it possible to show that the known particles (leptons, hadrons, quarks, gluons, photons) essentially determine the specifics of the processes of the microworld. Apparently, this list is far from complete, as is the theory of elementary particles itself.
As noted, the physics of elementary particles has a huge amount of empirical material and theory already provides a rational explanation of a significant part of it. However, it still lags significantly behind the experiment and is not an internally closed system of certain principles and concepts, although its conceptual apparatus is much more capacious and differs from the apparatus of previously existing theories.
Let us now consider in retrospect some of the attempts to construct a unified theory covering all particles and fields. There are two main trends here that are ultimately related to each other. The first of them originates from the idea of Louis de Broglie, which consists in using as a basis the simplest wave function of the spinor type, which describes a particle with a minimum non-vanishing angular momentum, i.e., the spin S = 1/2 (in fractions of h / 2π) ... Then, by combining these wave functions (eventually multiplying), we, under some additional conditions, obtain by a similar "fusion" all other possible wave functions of particles with spins 0.1; 3/2; 2 ... Combining two angular momenta + 1/2 and - 1/2, we get 0, combining two angular momenta + 1/2 and + 1/2, we get 1 (since spins + 1/2 can be oriented only in parallel either antiparallel). The fusion method succeeds, combining two Dirac equations describing spin particles ("fermions"), to obtain the Klein-Gordon and Proca equations, and in the particular case of vanishing rest mass, Maxwell's electrodynamics equations. In this way, in principle, it is possible to construct photons from neutrino-antineutrino pairs. The ideas of Louis de Broglie's neutrino theory of light were developed by Kronig, Jordan, A. Sokolov.
The weak point of the fusion method is the absence of any forces that condition the fusion itself. It remains unclear what causes, for example, neutrinos to turn into quanta of the electromagnetic field. The so-called nonlinear unified spinor theory of matter by W. Heisenberg tried to answer this question. The name of this theory is clearly unfortunate. It was about the creation of a unified theory of elementary particles and fields, and not about the theory of matter, for the only theory of matter, as an objective reality that exists outside and independently of the cognizing subject, is dialectical materialism. If we take some unified spinor field as the basis of the new theory, then it is capable of interacting only with itself. This leads to the appearance of the so-called nonlinear terms in the Dirac equations (which were first introduced by D. Ivanenko back in 1938), and then considered in more detail by W. Heisenberg (193, 441-485; 34).
This theory does not give exact values of particle masses and coupling constants, but, undoubtedly, this is one of the attempts that deserve attention, although it is not without its drawbacks. This is only a research program that should not be overestimated, as has already been the case in individual articles published in our press.
It should be borne in mind that already several years ago the incorrectness of the mathematical interpretation of the Heisenberg spinor theory was revealed, and it was also shown that the indefinite metric introduced by Heisenberg leads to a violation of microcausality. It can be assumed with good reason that Heisenberg's concrete attempt to create a unified theory of elementary particles has so far failed, but the direction of research he has chosen should not be discounted. In recent years, there has been a kind of return to the ideas of W. Heisenberg.
In 1958 in the USA, when Pauli was reporting on Heisenberg's theory, N. Bohr, who was present at the discussion, replied: "For a new theory, Heisenberg's theory is not crazy enough" (crasy) (23, 20). N. Bohr meant the absence in this theory of an unusual, outlandish idea. In our opinion, physicists do not yet have such an idea. Academician I. Tamm considered the most promising direction in the development of the theory of elementary particles attempts to radically revise our space-time concepts as applied to ultra-small scales. He refers to the statements of Academician L. T. Mandelstam about the inapplicability of the usual concepts of space and time to nuclear scales, as well as to the work of H. Snyder (1947), who proposed a method for quantizing space and time, leading to the conclusion that space is discrete. Snyder showed that the quantized space, that is, the space of non-commuting coordinates, is discrete and at the same time isotropic. However, Snyder's ideas were hardly further developed with the exception of the works of Golfand and Kadyshevsky.
VG Kadyshevsky (50, 1961, 136. (1)) proposed to introduce into the theory of elementary particles the universal length "l" on the basis of changes in the geometry of space-time. He believed that the new geometry should satisfy the following conditions:
a) the form S 2 = X 2 0 - X 2 2 is not invariant to the transformation of coordinates, while the group of motions would admit a lower degree of isotropy of the 4-space than the Lorentz group;
b) non-invariance of the interval and the presence of a universal length would be the reasons for nonconservation of parity;
c) there must be a subgroup for which S 2 is an invariant, so that one can describe the symmetries of large regions of the 4-space - large in comparison with the elementary length "l". The author connects the length "l" with the value of C - the universal constant of weak interaction. After highlighting the factors " h"and" C "for" l "is followed by the value 7 * 10 -17 cm. This and subsequent works are very interesting, but so far the possibilities of this theory remain unclear.
In 1959, the Canadian physicist H. Koisch and the Soviet physicist I.S.Shapiro in their studies considered a discrete space consisting of a finite number of elements and showed good agreement between a number of conclusions and experimental data. It is also one of the possible search paths, bringing closer to the creation of a systematics of elementary particles, to a new generalizing physical theory. However, IS Shapiro, speaking in 1962 at the Conference on the Philosophical Problems of Elementary Particle Physics, assessed his work as an initial stage, very far from the creation of a theory that allows comparison with experiment. A philosophical analysis of this problem was given by R. A. Aronov (31.1957.3).
In physics, questions were considered about the so-called spectral representations and dispersion relations. In the opinion of a number of physicists, this was a kind of new stage in its development, when the analytical properties of physical quantities (for example, scattering amplitudes) were investigated as they continued from real values into the complex region. The application of the theory of functions of a complex variable to these quantities gave extremely important results. Mandelstam (99) introduced double dispersion relations, considering the complex values of not only energy, but also momentum. Regge proposed a generalization of the S-matrix formalism and dispersion relations to complex angular momentum values. As a result of the application of "registika", the ratios were determined between the amplitudes of the probabilities of various scattering processes: ππ, πN, NN, etc. at high energies. However, there are data (in the field of ultrahigh energy physics) that limit the claims of the "regis" to the comprehensiveness of their ideas.
Academician I. Tamm considered the dispersion theory to a certain extent phenomenological, since it, without going into the mechanism of elementary physical phenomena, extracts from the experimental data the numerical values of a number of parameters included in it and then correctly predicts the results of a much wider range of experiments than those on on the basis of which these parameters were determined. In the second edition of this book, we wrote (p. 194) that although at first glance there is a close unity of theory and practice, it seems to us that the theory itself is of a prescription nature. We agreed with I. Tamm's conclusion that "the success of the dispersion theory (both present and future) does not at all solve the main problem of creating a new physical theory based on a limited number of general principles and postulates" (23, 21). The subsequent development of physics has confirmed these assumptions. There were many other attempts to build a theory of elementary particles. Let's briefly analyze some of them.
Fermi and Yang proposed to consider the p-meson as formed from a nucleon and an antinucleon using some still unknown forces acting at extremely small distances p + ¯p = π. The huge potential binding energy "eats up" almost the entire mass of both nucleons, leaving only the mass of the pion. The proposal of S. Sakata, who based the theory on p, π, λ and three corresponding antiparticles, aroused interest. Then, by combining these basic particles, you can get all pions, K-mesons and hyperons. “This model,” S. Sakata wrote, “attracted attention, since it not only served as a“ substantial ”basis for the structure of strong interaction, but also made it possible to explain the mass spectrum of composite particles and predicted the existence of resonant particles that were then discovered” (74, 168). However, the nature of the adhesion forces remained unclear. A minimum of three main particles are needed to ensure the presence of such fundamental properties as charge, isospin, strangeness (represented by the λ-hyperon). It is clear, again, that the basis should be based on "rotating" spinor particles, fermions, since in the absence of "rotation" there would be nowhere to get it. We see here a kind of revival of the theory of Helmholtz and Kelvin, who tried in the middle of the 19th century. build matter from hypothetical ether vortices.
When constructing a "composite" model, Sakata proceeded from the following view of elementary particles: "... I consider elementary particles as one of an endless set of levels of the structure of matter, qualitatively different from each other and in the aggregate forming nature. My point of view is based on the provisions of the materialistic dialectics ... it is necessary first of all to establish whether more than thirty types of elementary particles discovered to date belong to one or several different levels of the structure of matter "(31, 1962, 6, 134). Sakata and his collaborators tried to include leptons in their scheme. Leptons e -, v, μ and some "baryon" field B (the so-called B-matter) are taken as a basis. Combining one of the leptons with the B field, they get the main particles. Thus, the similarity noted by Marshak - Gamba - Okuba (203) between baryons (p, π, λ and leptons v, e -, μ -) is realized. The same symmetry is realized in the nonlinear spinor theory of particles.
Marshak called his considerations of symmetry "Kiev symmetry", since they were born at the symposia of the Kiev conference on high-energy physics in the summer of 1959. We are talking (as we have already mentioned) about some analogy that existed between the triplets of baryons (p, π, λ) and leptons (v, e -, μ -). Any term of the four-fermion interaction, with the participation of the operators of these particles, can be contrasted with a similar term obtained from the first by replacing λ by μ -, π by e -, p by v. Then, if the process is allowed / forbidden before the replacement, then it remains allowed / forbidden after replacing one particle from the baryon / lepton triad with a "symmetric factor" from the lepton / baryon triplet. Marshak points out that he carefully analyzed all the experimental data and did not find a single case that contradicts the indicated "symmetry", but the nature of this symmetry remains unclear. Now that the quark model has already been created, it becomes possible to interpret the Kiev symmetry as the correspondence of four quarks - u, c, d, s to four leptons - v е, v μ, e, μ, but the nature of this symmetry is still not well known.
We know that any, even the most successful, attempt to create a unified theory of matter and field will inevitably be temporary, transient. Further theoretical and experimental penetration into the depths of the microworld and, more and more extensive studies of phenomena in space, inevitably violating any single picture, will lead to its disintegration into separate elements, until tendencies to unification at a higher level reappear.
The introduction of various concepts that reflect the real properties of particles (isotopic spin, strangeness, baryon charge, etc.) brought us closer to the correct classification of particles. The principle of symmetry plays a huge role in the classification of microparticles. It is easy to see that elementary particles of each class (photons, leptons, mesons, hyperons) have certain symmetry properties common to them, but we will consider this issue in more detail in the course of the further presentation.
J. Chu, M. Gell-Mann and I. Neeman (21, 5E) proposed a new classification of strongly interacting particles of matter, in which the separation of particles into elementary and complex (composite) ones loses its meaning. These authors proposed to consider particles united into groups (supermultiplets) so that particles with different rest mass in each group can be considered as different excited states of the same system. The mass spectrum of particles in this scheme has a close analogy with the spectrum of energy states of an atom. Each of the particles can be regarded with the same basis as both simple and complex. To find the mass spectrum, two methods are proposed: one of them is based on the properties of symmetry and group theory, the other is based on the use of the so-called Regge trajectories, i.e., curves connecting the mass of a particle with its internal angular momentum (spin) in each group.
Many physicists currently consider the Gell-Mann octet scheme to be the most successful. It is based on the principle SU(3) symmetry. Eight known baryons are considered to be a supermultiplet corresponding to the highest symmetry; this symmetry is broken, and the supermultiplet splits into isotopic spin multiplets. Strongly interacting particles are described in the space of "unitary spin", which has eight components: the first three of them are isospin components, the next four play the role of operators that change the strangeness, and the last is proportional to the hypercharge. When the higher symmetry ("unitary") is broken, isospin and hypercharge are retained, and the components of the unitary spin corresponding to strangeness change; as a result, the supermultiplet splits into isotopic spin multiplets. Thus, the Gell-Mann theory to some extent takes into account the deep dialectical unity of symmetry and asymmetry in the world of elementary particles. This is what allowed this theory to unite strongly interacting particles according to a harmonious scheme and at the same time reflect their specificity (asymmetry of properties). The Gell-Mann octet scheme once again reveals the tremendous heuristic power of the symmetry principle. Within the framework of the "eightfold path" hypothesis, on the basis of symmetry and conservation laws, the existence of the Ω-hyperon was predicted, which was discovered at the Brookhaven accelerator in the United States (214). At one time we wrote that the successes to which the taking into account the property of unitary symmetry in the theory led to hope that experimental studies will lead to the discovery of other particles predicted by the theory with a fractional electric charge (± 1/3 and ± 2/3 of the electron charge) , the so-called quarks. The subsequent development of physics justified these hopes.
Let us point out some more attempts to systematize elementary particles. Thus, several years ago M.A.Markov (204) proposed an original model Maximonov... Based on the ideas of the general theory of relativity, he showed that the macro- and microcosm can closely merge with each other. The formal basis for the introduction of new hypothetical elements was the fact that two combinations with the dimension of mass can be made from the most important world constants of modern physical theory. One of these quantities has a numerical value of one millionth of a gram, while the other is ten times greater. The maximons introduced in this way are 10 19 times the mass of real hadrons (strongly interacting particles). Maximons are so heavy for their spatial dimensions that "these particles cannot be found in any vessel on the Earth's surface. Under the action of gravity, they fall to the center of the planet ... on accelerators of the distant future are excluded "(53.1966.51, 878).
Analysis of existing models shows some difference in the approach of their authors to the problem of systematization of micro-objects. Some proceed from certain properties of elementary particles and fields and try to solve the problem of the structure of micro-objects by introducing new properties of space-time symmetry, others, on the contrary, retain the known properties of space and time, but to explain the structure of micro-particles, they introduce new characteristics of the properties of material micro-objects and fields. This difference in approaches to solving the same problem is quite justified.
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The problem of elementary particles
At different stages of advancement "into the depth" of the 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 the 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 that did not have an internal structure. After the discovery of the neutron in 1932, it seemed that the main building blocks of which ordinary matter is built, it seemed, were protons, neutrons, electrons and photons.
But, since 1933, the number of discovered elementary particles is growing rapidly. When their number exceeded a hundred, it became clear that such a huge number of particles could not act as elementary constituents of matter.
They tried to classify 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 we know belong to leptons, and the proton and neutron to baryons. There is one more 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 a quark model was proposed in the 60s, based on the hypothesis of the existence of new truly elementary particles, which were called quarks. In the framework of the quark model, all baryons are considered as combinations of three quarks, and mesons are combinations of a quark and an antiquark.
Basic characteristics of elementary particles
The main characteristics of elementary particles are as follows:
Weight - m
Lifetime - 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 best known. The neutrino mass is possibly zero as well. The electron is the lightest of the stable particles with a nonzero mass (me = 0.911 · 10-30 kg). The proton has the lowest mass among baryons
(m p = 1.672 10 -27 kg). The mass of the neutron is slightly greater than the mass of the 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, with lifetimes ranging from a few microseconds to 10-23 s.
Electric charge. The electric charges of all studied elementary particles (except for quarks!) Are integer multiples of e
1.6 · 10-19 C (e is an elementary charge, numerically equal to the charge of an electron, or proton). In our world, the universal law of conservation of electric charge operates: the total electric charge of an isolated system is conserved.
Baryon (B) and lepton (L) numbers (charges) characterize the belonging of a particle to the class of baryons or leptons. Baryons have no lepton charge ( L = 0), for baryon particles B = 1, for antiparticles B = -1. Leptons have no baryon charge, and their lepton charge is L = 1 - for particles (electron, neutrino) and, accordingly L = -1 - for antiparticles (positron, antineutrino).
The main property of elementary particles is their ability to interconvert, which occur only under the condition that all types of charges considered above are preserved: electric, baryonic, 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 intrinsic (spin) moment, which is measured in
units h (Planck's constant) or ћ = |
(h strikethrough). |
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In units of ћ, the spin of all elementary particles takes on the values or |
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integers: 0, 1, 2, ... or half-integers: 1 |
, … |
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Particles with half-integer spin are called fermions, and particles with integer spin are called bosons. Fermions obey the Pauli 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 other hand, all tend to get into the same state. All bosons are particles-quanta of some field. Of all the bosons, photons are the most abundant in the universe.
34 A quantum state is fully 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 "highly individualists", while bosons are the most real "collectivists".
Fundamental fermions - leptons and quarks
At present, leptons and quarks, whose spin is equal to ½, are considered to be truly elementary particles, of which all matter in our world is built.
The family of leptons consists of particles of three generations: to first generation include the electron e - and electron neutrinoν e; second generation- muon μ and muonic neutrinoν μ and, finally, third generation–
taon τ - and taon neutrino ν τ:
μ − |
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ν e |
νμ |
ν τ |
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Electron, muon and taon appear in a pair only with their own neutrinos. Huge penetrating ability, lack of charge and extremely small, perhaps 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 can easily penetrate the Earth and are able to pass through a layer of lead several light years thick. Meanwhile, neutrinos, along with photons, are the most abundant particles in our world. If all matter, including all galaxies and intergalactic dust, is uniformly stirred throughout the entire volume of the Universe, then for every cubic meter of space there will 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 β-decays of nuclei,
at which there is a transformation of a proton into a neutron (the so-called β + - decay) and a neutron into a proton:
→ 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 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 is associated with energy costs and can only occur inside the nucleus. β + - decay is accompanied by the birth of a particle completely analogous to an electron, but with an opposite electric charge, which is called a positron +1 e 0.
In addition to the electron (or positron), another elementary particle is involved in β - decays, which is called neutrino - 0 ν 0 (particle,
accompanying β - - decay).
Antiparticles
The existence of an electron and a positron suggests that other elementary particles can also have their "twins". Indeed, practically 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 (photon). In principle, there can exist an antiatom, the nucleus of which consists of antiprotons and antineutrons, and electrons are replaced by antielectrons (positrons), an antimolecule and, finally, antimatter, the properties of which will not differ in any way 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 Lat.annihilatio -
destruction, disappearance) - 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 when they collide into photons (electromagnetic radiation):
1 e0 + +1 e0 → 2γ
The opposite effect is also possible - the formation of an electron-positron pair in the collision of two photons. It is clear that the photon energy should be no less than the doubled electron rest energy E γ> 2m e c 2 (slightly more
1 MeV).
Our world is made up of matter. On the 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 close coexistence of particles and antiparticles is impossible. The few antiparticles that can be produced in laboratory conditions sooner or later die. The long-term existence of stable antiparticles (for example, antiprotons or positrons) is possible only at a low density of matter - in special storage rings for 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 is called quarks. There are six types of quarks, (physicists call them "flavors" - flavors) which, like leptons, are grouped in pairs and form three generations. First generation- u and d quarks (up - up and down
Lower); second generation - s and c quarks (strange - strange and charm -
charmed) 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 projections of the vector 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 that physicists have called flavor (weirdness, 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 (in this case, the quark charge is positive), or 1/3 of the electron charge (the sign of the charge is negative in this case).
All baryons are combinations of three quarks. Nucleons - the fundamental basis of atomic nuclei, are the lightest baryons and consist of first generation quarks. The proton is composed 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 in this case turns out to be equal to unity (2/3 + 2 / 3–1 / 3 = +1), and the neutron charge to 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 interconversions of quarks (u d) receive a new explanation.
Mesons are obtained from a combination of a quark-antiquark pair. It's clear that |
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the baryon number of mesons is zero, |
spin is |
zero or one. |
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Combinations of three antiquarks form antibaryons (antiprotons, |
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antineutrons, etc.). |
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Table 1 lists all fundamental fermions - |
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structural units of the structure of matter. |
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Table No. 1 |
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Fundamental fermions |
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Fundamen- |
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Generations |
III-th Electric |
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fermions |
generation |
generation |
generation |
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charged |
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electron |
−1 |
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νμ |
ντ |
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neutrino |
electronic |
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charmed |
true |
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beautiful |
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The whole variety of hadrons arises due to various combinations |
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given |
aromas. |
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there correspond bound states constructed only from u and d quarks. If in the 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 can be obtained from various combinations of quarks symbolized the main triumph of quark theory. However, all efforts to find single quarks were in vain. A paradoxical situation has developed. 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 (in fact, completely analogous to Rutherford's experiment), it was found that inside hadrons, electrons are scattered by 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 snatch quarks from hadrons. This phenomenon is called "confinement"
(confinement- captivity, eng.).
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 unite into nucleons, nucleons into nuclei, nuclei and electrons into atoms, atoms into molecules? Why are there clusters of matter in the Universe in the form of planets, stars, galaxies? What is the nature of the forces that cause all those 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 versatile. The gravitational interaction acts between any objects with mass or energy. It is gravity that does not allow the Universe to fall apart, collecting matter into planets and stars, keeping planets in orbits, "tying" stars into galaxies. In general, on an astronomical scale, gravitational interaction plays a decisive role. In the microcosm, gravity can be neglected in comparison with other more intense interactions.
Electromagnetic interaction inherent in all particles,
having an electric charge. Like gravitational, electromagnetic interaction is long-range, and the law that determines the force acting between point resting charges is similar to the law of gravitation - this is Coulomb's law known from the school:
m 1 m 2 |
q 1 q 2 |
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However, unlike gravity, which is always attraction, electric attraction exists only between charges of opposite signs, while charges of the same name are repelled. It is thanks to the electromagnetic interaction that the formation of atoms and molecules is possible. Intermolecular forces that determine the properties of various aggregate states of a substance are also electrical in nature. Most of the observed physical forces (elasticity, friction, etc.) are actually reduced to it, it is this that underlies the chemical transformations of substances and all observed electrical, magnetic and optical phenomena.
Strong and weak interactions manifest themselves only in the microcosm, at the subnuclear level.
Strong interaction is inherent in quarks and formations of quarks - hadrons. The main function of strong interactions 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 is 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 the particles, that is, in the transformation of one quark into another (the same applies to leptons).
In the absence of a weak interaction, not only a proton and an electron would be stable, but also muons, π - mesons, strange and charmed particles that decay as a result of weak interaction. If it was possible to "turn off" the weak interaction, then the Sun would go out,
since the process of transformation of a proton into a neutron (β - decay) would be impossible, as a result of which four protons are converted 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.).
Characteristics of fundamental interactions
The intensity of interactions can be judged by the speed of the processes that they cause. Usually compared with each other process speed at an energy of 1 GeV, typical for elementary particle physics. At such energies, the process due to the strong interaction
occurs in a time of 10-24 s, the electromagnetic process in a time of 10-21 s, while the characteristic time of the processes occurring due to weak interaction is much longer: 10-10 s.