The concepts of the macroworld of classical physics and the concept of the microworld of modern science. Systematics of elementary particles. Superelementary particles The problem of the structure of elementary particles

About 400 are now known. elementary particles. Some of them "live" for a very short time, quickly turning into other particles, managing to fly distances equal to the radius of the atomic nucleus (10 -12 - 10 -13 cm) during their existence. The minimum time available for experimental measurement is characterized by a value of about 10 -26 s. Some elementary particles turned out to be unexpectedly heavy - even heavier than individual atoms.

Modern physicists pay much attention to the systematization of elementary particles, to the disclosure of the internal unity both between them and between the fundamental types of interaction corresponding to them - strong, weak, electromagnetic and gravitational.

The intensity of weak interaction is 10-11 orders of magnitude (10 10 -10 11 times) less than the intensity of nuclear forces. Therefore, it was called weak, its radius of action is less than 10 -15 cm. The electromagnetic interaction at distances commensurate with the radius of action of nuclear forces is only 10 2 -10 3 times weaker than them. The weakest at these distances is the gravitational interaction, the intensity of which is many orders of magnitude lower than the weak interaction.

Even the weak interaction exceeds the gravitational interaction by many orders of magnitude. And the force of the Coulomb, electric repulsion of two electrons is 10 42 times greater than the value of their gravitational attraction. If we imagine that the electromagnetic forces that “attract” electrons to the atomic nucleus weaken to the level of gravitational forces, then the hydrogen atom would become larger than the part of the Universe that we see. Gravitational forces increase very slowly with decreasing distances. They become predominant only in fantastically small intervals less than 10 -32 cm, which are still inaccessible for experimental research. With the help of the experiment, it is now possible to "view" distances close to 10 -16 cm.

These four types of fundamental (lying in the very foundation of matter) interactions are carried out through the exchange of the corresponding particles, which serve as a kind of carriers of these interactions. The radius of action of forces depends on the mass of particles. The electromagnetic interaction is carried by photons (the rest mass is equal to zero), the gravitational interaction is carried by gravitons (so far hypothetical, experimentally not established particles, the mass of which should also be zero). These two interactions, carried by massless particles, have a large, possibly infinite range. Moreover, only gravitational interaction generates attraction between identical particles, the other three types of interactions cause repulsion of particles of the same name. The carriers of the strong interaction that binds protons and neutrons in atomic nuclei are gluons. This interaction is characteristic of heavy particles, called hadrons. The weak interaction is carried by vector bosons. This interaction is characteristic of light particles - leptons (electrons, positrons, etc.).

The diversity of the microcosm implies its unity through the interconvertibility of particles and fields. The transformation of a "pair" - a particle and an antiparticle - into particles of a different "sort" is especially important. The first to discover was the transformation of an electron and a positron into electromagnetic field quanta - photons and the reverse process of "generating" pairs from photons with a sufficiently high energy.

At present, the development of the problem of systematization of elementary particles is associated with the idea of ​​the existence quarks - particles with a fractional electric charge. Now they are considered "the most elementary" in the sense that all strongly interacting particles - hadrons - can be "built" from them. From the standpoint of quark theory, the level of elementary particles is the region of objects consisting of quarks and antiquarks. At the same time, although the latter are considered at this level of knowledge to be the simplest, most elementary of the known particles, they themselves have complex properties - charge, "charm" ("charm"), "color" and other unusual quantum physical properties. Just as in chemistry one cannot do without the concepts of "atom" and "molecule", so elementary particle physics cannot do without the concept of "quark".

Thus the list hadrons - heavy particles characterized by strong interaction - consists of three particles: quark, antiquark and linking them gluon. Along with them, there are about ten light particles - leptons (electrons, positrons, neutrinos, etc.), - which correspond to the weak interaction. Also known photon - carrier of electromagnetic interaction. And still hypothetical, only theoretically predictable, remains graviton, with which the gravitational interaction is associated. So far, nothing is known about the internal structure of leptons, photons, and graviton. Now there already exists a more or less specific idea of ​​synthesis, the relationship of weak, strong and electromagnetic types of interaction. The possibility of explaining their relationship with the gravitational interaction is also found. All this testifies to the gradual realization of the fundamentally unlimited possibility of theoretical thinking in the cognition of the unity of the world, which remains infinitely diverse in its manifestations within the framework of unity.

Literature for Chapter 10

Barashenkov V. S. Are there boundaries of science: quantitative and qualitative inexhaustibility of the material world. - M., 1982.

Heisenberg V. Physics and philosophy: Part and whole. - M., 1989.

Zeldovich Ya.B., Khlopov M.Yu. The drama of ideas in the knowledge of nature: Particles, fields, charges. - M., 1988.

Markov M.A. On the nature of matter. - M., 1976.

Pakhomov B.Ya. Formation of the modern physical picture of the world. -M., 1985.

Sachkov Yu.V. Introduction to the probabilistic world. - M., 1971.

CHAPTER 11

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Introduction

1. Origin and development of ideas about the 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. The ideas about nature in this period were purely natural-philosophical in nature, the observed natural phenomena were explained on the basis of mentally assembled philosophical principles. The greatest achievement of natural science in 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, which are 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 forming it, was the first theoretical program. That doctrine of Democritus, vacuum is necessary to explain the mechanical placement of bodies in space and their deformation (compression, elongation, and others) under the influence of external forces. Atomism explained the essence of the flow of natural processes by the mechanical mutual influence of atoms, their attraction and repulsion. The mechanical program for explaining nature, first put forward in ancient atomism, was realized in classical mechanics, which marked the beginning of 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 microcosm, which was born as a result of a critical study of the concepts of classical mechanics, which are applied only in the microcosm. Formation scientific ideas about the structure of matter refers to XVI 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 a subject of scientific research. The selection of individual characteristics of the object provided an opportunity to create theoretical models and test them on the basis of a 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 the quantum

quantum elementary particle

During the transition of physics from the study of the macrocosm to the study of the microcosm, the ideas of classical physics about matter and field have changed radically. 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 wave property and the property of corpuscularity. This phenomenon is called corpuscular-wave dualism.

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 snag as the “ultraviolet catastrophe”. According to the calculations made on the basis of the formulas of classical electrodynamics, the intensity of the radiation of only dark objects increased indefinitely. This was contrary to practice. From studies conducted on heat radiation, M. Planck came to the conclusion that in the process of radiation, energy is emitted not in an arbitrary amount and unlimitedly, but in indivisible portions - quanta. The energy of a quantum is determined by the number of vibrations corresponding to radiation (V) and the universal constant, called Planck's constant: E=hn. As Planck noted, the arrival of the idea of ​​a quantum in physics cannot yet be associated with the creation of quantum theory, however, December 14, 1900, the date of the appearance of the quantum energy formula, became the date of 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 met the discovery of the influence of an elementary quantum with a high spiritual uplift and developed it in his work. There was A. Einstein. In 1905, by applying the idea of ​​the quantum 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 is necessary to accept the corpuscular structure of light. The quantum theory of light or Einstein's photon theory confirmed that along with the fact that light is a wave phenomenon of propagation in the world 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 vibrations (n). Monochromatic light of various colors (red, yellow, green, blue, violet and others) consist of light quanta of different energies. Einstein's idea of ​​light quanta made it possible 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 birth of the interpretation of the photoelectric effect in a similar scenario, it was confirmed by the experiments of the American physicist R.E. Millikan. Discovered in 1923 by the American scientist A.Kh. Compton 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, a paradoxical situation has arisen: it has become 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 - the frequency (n). Like all great natural scientific discoveries, the quantum theory of light has acquired an essential ideological, theoretical and cognitive character.

The concept of phonons-quanta of the electromagnetic field has become 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 an opportunity for the Danish scientist N. Bohr to develop a new model of the atom.

1.1 TBohr's theory of the atom

In 1913, the Danish scientist Niels Bohr, applying the principle of quantitativeity 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 by Rutherford in 1911 resembled the solar system: the nucleus was located in its center, and electrons revolved around it in circular orbits. The nucleus was positively charged, the electrons had a negative electric charge. Attractive forces in solar system in the atom were replaced by electrical forces. The positive electric charge of the atomic nucleus, which was equal to the ordinal 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 the electrons, in order not to lose their stability, must revolve around the nucleus. As you know, circular motion is characterized by centrifugal acceleration. According to the laws of classical electrodynamics, rapidly moving electrons must necessarily radiate electromagnetic energy. However, in this case, the electrons in a very short period (10-8 seconds), spending their energy on radiation, must fall on the nucleus. We know this well from everyday experience. If electrons fell on the nucleus, the 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 connected with 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 whole. Experience shows that the emission spectrum of an atom is linear. In other words, Rutherford's planetary model of the atom does not get along 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;

Rutherford's nuclear model of the atom;

quantum character of emission 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 coexist 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 the atom are neither emitted nor absorbed.

The second postulate: an atom only emits or absorbs a portion of energy when the 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 the electron's momentum, the Planck constant is completely likened to the relative 2p:

where m, n, r are respectively the mass of the electron, the speed and radius of the stationary orbit along 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 unacceptability of its laws to stationary states. It is not so easy to agree with the idea of ​​radiation of energy by electrons in certain selected orbits. At the same moment, the question arises: “Why?” However, due to the fact that this postulate was adequate to the results of experiments, physicists were forced to accept it. From the second postulate follows the conclusion that the energy of the atom is emitted in portions. The transition of an electron from one orbit to another is necessarily accompanied by integer numbers of energy quanta. So, 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 moment that characterizes rotary motion electrons. Bohr's postulates explained the stability of the atom: in stationary states, an electron without the existence of external causes does not emit electromagnetic energy. Only now it has become clear why, with an unchanged estimate of the states, the atoms of chemical elements do not radiate electromagnetic waves. The model of the atom 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 facts of experience, the later application of this model to many-electron atoms encountered certain difficulties. No matter how accurately the theorists tried to describe the motion and orbit of electrons in the atom, the difference between theoretical results and experimental data remained large. However, in the course of the development of quantum theory, it became clear that these differences are connected mainly with the wave property of electrons. The wave length of an electron moving along a circular orbit in an atom was part of the measurements of the atom and was approximately 10-8 cm. , when the wave length of the particle compared to the system of changes will be so small that it will not be taken into account. In other words, one must 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 represent the structure of an atom on the basis of ideas about the orbits of presumably point electrons, therefore the inner orbits of the atom have become ideal objects, they do not even exist in reality. According to their wave nature, the electrons and their electric charge are allegedly unevenly distributed over the atom and have a low density of electrons at some points, and a higher density at others. The description of the electron charge density distribution inside an atom is given in quantum mechanics: at some points, the electron charge density reaches its maximum. The curve that unites the points of maximum marks of the electron charge density is formally called the orbit of the electron. 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 of development modern physics. Bohr's atomic theory, based on the addition of a small amount of new reasoning, 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 capable of explaining similar results of the simplest experiments related to the structure of the atom. Bohr's postulates, alien to classical physics, having violated its integrity, in turn, were able to explain only a small area of ​​experimental data. Therefore, the idea is born that Bohr's postulates, which discovered new, hitherto unknown to science properties of matter, at the same time partially, did not fully reflect them. Bohr's theory, and his postulates that 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 the Bohr model of the atom cannot be taken literally as it was before. It would be wrong to visually describe the processes of the atom in the form of mechanical models created by analogy with the phenomena of the macrocosm. It soon became known that the notions 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 partseggs and the problem of their structure

The problem of the structure of matter has been one of the urgent problems that has always been at the center of attention of natural science, especially in its advanced field - physics. Convexly reflecting the relationship between philosophy and natural science, this problem has not only philosophical, but also practical and production-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 connected with the discovery and use of nuclear energy, which laid the foundation for the "atomic age".

Modern physics has won great achievements in the field of studying the structure and properties of matter. However, despite this, in the field of the structure and properties of matter, nature has many secrets that have not yet been discovered. Penetrating into the depths of theoretical cognitive matter and discovering new levels of its structure, we believe this more and more. Physics on present stage of its development has embarked on 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 embark on this path. Before gaining certain achievements on this path, it went through a long and difficult path of development, 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 dwelling on the successes of scientific knowledge, this doctrine, which was enriched and developed, combined four sides organically related to each other: first of all, this doctrine is an atomistic doctrine, because according to this doctrine, every body, every physical region is formed from microparticles and microregions , secondly, this doctrine is a statistical doctrine, because, based on statistical representations, it determines the properties and patterns of movement of micro-objects, their mutual influences and transformations by statistical laws, thirdly, this doctrine is a quantum theory, so the properties and patterns of movement of microparticles qualitatively different from the properties and laws of motion of microscopic bodies determined by classical physics, and finally, this teaching is a relativistic teaching, because in this theory the connection between space, time and matter is described by means of a relativistic theory - the theory of relativity.

Not dwelling on the field of knowledge of the structure and properties of matter, developing human knowledge has revealed 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 level of an atom 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. At present, 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, strong accelerators that create conditions of high energy and gigantic speeds, the existence of more than 300 elementary particles was discovered. One part of the elementary particles was discovered in the 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 side inherent in the natural science concept that, like all physical concepts, the concept of “elementarity” is relative, at different stages of the development of scientific knowledge it acquires different meanings. Until the mid-60s of our century, ideas about elementary particles resembled one of the views on atoms expressed by Democritus. However, these first naive ideas about elementary particles did not last long: it was soon proved that there are no immutable, impenetrable, structureless particles. Under the influence real facts the concept of "elementary" has undergone a change and in general everything that can be called an "elementary particle" has assumed 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 every two meanings expressed by the concept of "elementary particle", we can say in the full and broad sense of the word that the called "elementary" particles are such material formations that consist of other particles known to science and in all processes as a whole are in mutual influence, which include physical quantities characterizing 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.

The physics of elementary particles is, in the words of 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 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 figure 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 the achievements of scientific knowledge in this area. The implementation of such classifications is connected with the description of the properties and basic characteristics of elementary particles.

At present, a wealth of properties of the known sciences of elementary particles 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 by the abstract language of mathematics are as follows: mass, charge, average period of existence, spin, isotropic spin, singleness, pairing, leptin charge, borion charge, mutual influence. Let us 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 an electron (me=9.1×10-31 kg). At present, the classification of elementary particles depending on the magnitude of their rest mass is more widespread. According to this classification, all elementary particles fall into 4 groups: 1) light elementary particles - leptons. This includes the electron, neutrino and their antiparticles - positron, antineutrino, as well as positive and negative muons. 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, on the other hand, are not stable particles, having lived for two hundred millionths of a second, they decay, turn into an electron, a neutron and an 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 medium weight- mesons. This includes positive, negative and neutral pi-mesons with a mass of 270 me - the rest mass, and some types of ka-mesons with a mass of 970 me. All mesons are unstable, have a very short period of existence (up to 7-19 seconds).

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

4) hyperons - 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 a photon that 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 an 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 commonality (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, under certain conditions, uniting, 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 the particles of matter and the field, which are two types of matter, but also between the particles of matter themselves. As a result, it became clear that the particles of matter are not immutable and not simple, they can turn into each other in the process of mutual influence, they can be formed and absorbed by various complexes of particles. Another important property of elementary particles is the 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 of the particles do not have an electric charge. In addition to the photon and both mesons, each particle corresponds to an antiparticle of opposite charge. The reason why different elementary particles do not necessarily have the same indicators of electric charge and that some elementary particles are devoid of electric charge is not yet known to us. It is very possible that this is a manifestation of yet undiscovered deep internal regularities 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 neutron, millionon neutron, electron and proton. Stable particles play a decisive role in the structure of macrobodies. The rest of the particles are not stable. These particles, located in the interval of average existence from 10-10 to 10-24 seconds, eventually divide into other particles. Quasi-stable elementary particles with average periods of existence of 10-10 to 10-24 seconds are called resonances. Due to the short period of existence, these particles cannot leave the atom or the nucleus of the atom and decay 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 unique to them and has no analogue in macroscopic physics; its description as a moment of mechanical impulse is in itself rough and inaccurate. We can look at the 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 it can neither be increased nor decreased. The spin determines the general nature of the type of statistics included in the particle (Bose-Einstein and Fermi-Dirac statistics) and the doctrine describing its motion. The spin of a proton, neutron and electron is equal to 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 can no longer be possible, in the same situation there can be several bosons. 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, at present the connection of these properties with the properties of symmetry and asymmetry of space has been determined. Spin is considered as a manifestation of the degree of internal independence in the motion of elementary particles. Thus, each elementary particle is characterized by 4 degrees of independence: three of them are the 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 a 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 is found in both charged and uncharged particles. It is assumed that a certain part of the magnetic moment of charged particles is due to their location in space. For example, it is assumed that the magnetic moment of protons and neutrons is due to the current created by the clouds of mesons gathered around them. Let's take a broader look at this issue. It is known that despite the fact that the 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 mainly determined by its internal structure. AT this case How should the creation of the magnetic moment of the neutron 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 neutron magnetic moment observed in the experiment 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 the baryon. The Leptonian 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 quantity refers to right and left symmetries. In the theory of elementary particles, the coordinates of each particle are characterized by a wave function y, which can change and 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 as -1. One of the very important characteristics of elementary particles is also mutual transformation, accompanied by emission and absorption of field quanta corresponding to elementary particles during the period of mutual influence. These processes, which differ from each other by the intensity of the flow, determine the division of the mutual influence inherent in elementary particles into 4 types: strong, electromagnetic, weak and gravitational mutual influences. The properties of elementary particles are mainly determined by strong electromagnetic and weak mutual influences. Strong mutual influences occur at the level of the nucleus of an atom, their constituent parts consist of mutual attraction and repulsion. Mutual influence forces, called core forces, spread 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 atomic nucleus. Despite the fact that electromagnetic mutual influences are weaker than strong mutual influences by about 1000 times, the radius of their influence approaches infinity. This type of mutual influence is characteristic of electrically charged particles. The carrier of electromagnetic mutual influence is free from electric charge and photon rest mass. A photon is a quantum of an electromagnetic field. Through electromagnetic mutual influences, uniting the nucleus of an atom and an electron into a single system, atoms are created, uniting, 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 converting a neutron in a nucleus into a proton, an electron and an antineutrino (n0® p+ + e- + n), can spread 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 the strong mutual influencing forces. However, for ultra-small distances (in the order of 10-33 cm) and ultra-high energies, gravitational forces acquire significant significance, 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 at the same time several types of mutual influence act between elementary particles, and the properties and structure of the particles are determined by the commonality of all types of mutual influence that take part. For example, a proton, which is a part of the hadronic type of elementary particles, takes part in a strong mutual influence, and in an 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 process of b decay of a neutron, that is, in weak mutual influences, thus, it is associated with weak mutual influences. And finally, the proton, as a material entity with mass, takes part in gravitational mutual influences. In contrast to the proton, a number of elementary particles take part in all types of mutual influence, but only in some of their types. For example, the neutron, due to the fact that it is an uncharged particle, does not take part in electromagnetic mutual influences, and the electron and muons do not take part in strong mutual influences. Fundamental mutual influences are the cause of the transformation of particles - their destruction and generation. For example, as a result of a collision of a neutron and a proton, two neutrons and one positive pimeson are formed. 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 passes into a particle of high energy and acquires a speed close to the speed of light, the size is about 10-13 cm. Changes due to electromagnetic mutual influences occur in 10-21 - 10-19 seconds, due to weak mutual influences changes , the process of decay of elementary particles) - in 10-10 seconds. The period of various changes taking place in the microcosm can be approached from the point of view of reasoning about creating mutual influences. Quanta of mutual influence of elementary particles are realized by means of physical fields corresponding to these particles. A field in modern quantum theory 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 empty in the true sense of the word, so in vacuum excitation there are quanta of the electromagnetic field - photons that realize electromagnetic mutual influence. In vacuum, in addition to the electromagnetic field, there are other physical fields, including the gravitational field, which has not yet been noted in the experiment on the so-called graviton experiments. Quantum field - a collection of quanta, is discrete. 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 concrete way is the continuity of the field manifested, its continuum? Both in quantum electrodynamics and in quantum mechanics, the field state is described uniquely not by observable real phenomena, but only by means of a wave function associated with a mutual concept. The square of the modulus of this function shows the possibility of observing the considered physical phenomena. The main problem of quantum field theory - description various types mutual influences of particles in the corresponding equations. This problem has found its solution so far only in quantum electrodynamics, which describes the mutual influences of electrons, positrons and photons. For strong and weak mutual influences, quantum field theory has not yet been created. At present, these types of mutual influence are not described by 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 at the present time proves the existence of complex particles that have the internal structure of particles that are considered "elementary". It became known that the proton and neutron undergo internal transformations as a result of the virtual processes occurring in them. 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 structureless, is in fact a complex particle. In its center is a dense core, called "kern", it is surrounded by positive pi-mesons. The complexity of the structure of "elementary" particles was proved by the quark hypothesis put forward in 1964 by the American scientist Gel-Mann and independently by the Swedish scientist Zweig. According to this hypothesis, elementary particles with relations characterized by strong mutual influences (hadrons: proton, neutron, hyperons) should be formed from quarks-particles, the charge of which is equal to one third or two thirds of the electron charge. Thus, the theory shows that for particle-forming marked quarks, the electric and baryon charge must be expressed as a fractional number. Indeed, the particles called quarks have not yet been discovered and remain hypothetical inhabitants of the microworld at the current level of development of science.

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 is still unclear. From the above data, it becomes clear that elementary particles are not elementary at all, they have an internal structure, they can divide and turn into each other. We still know very little about both structures. Thus, today, based on a number of facts, we can assert that the matter of elementary particles is a new kind, qualitatively different from more complex particles (nucleus, atom, molecule). At the same time, this difference is so significant that the categories and expressions used by us in the study of nuclei, atoms, molecules, macroscopic bodies (“simple” and “complex”, “internal structure”, “formed”) can also be applied to elementary particles. The concepts of "simple and complex", "constituent 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 than its constituent molecule. In the hierarchy of structures of material systems, the nucleus of an atom, atom, molecule, macroscopic bodies themselves create a single structural level. Therefore, the elements of the body, in comparison with the elements of the next level, are simpler, they act as their constituent parts. On the other hand, they are more complex than the elements located at lower levels and being their constituent parts. All systems, from the nucleus of the 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 in question and are simpler than the elements at a lower level into its constituent parts. In their meaning, the processes of unification 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, the decay products, together with the particles that generate them, are located on 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 not more complicated and not 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 elemental level the whole would consist of such a large accumulation. In this case, the mass of the whole can even be several times less than the masses of its components. For example, in a number of cases, as a result of the union of a nucleon and an antinucleon, a meson is obtained, the mass of which 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 that absorbs the released energy

can be so large that, as a result, the reaction products are not at all similar to the original particle. Therefore, in the world of elementary particles, the concepts of “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 energy mutual influences. Beginning 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 far exceeds the energy of their connection, it can be separated into its entire component part. For example, due to external energy, a molecule can be divided into atoms (Н2О®Н+О+Н), however, in this case, a striking 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 unchanged to a greater or lesser extent. According to modern concepts, the structure of elementary particles is described by means of continuously born and continuously dividing "virtual" particles. For example, meson annihilation (from the Latin word "annihilatio" - annihilation) is formed from continuously created and then disappearing virtual nucleons and virtual antinucleons. The 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. So far, a theory of the origin and structure of elementary particles that satisfies physicists has not been created. A number of prominent scientists have come to the conclusion that this theory can be created, taking into account only cosmic conditions. The idea of ​​the origin of elementary particles from vacuum in force, electromagnetic and gravitational fields acquires significant significance. Because the interconnection of micro, macro - and mega world is embodied only in this idea. In the mega-world the structure and mutual transformations of elementary particles are conditioned by fundamental mutual influences. Obviously, in order to adequately describe the structure of the material world, it is necessary to develop an apparatus of new concepts.

Bibliography

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

2. Kudryavtsev. Course in the history of physics. M., Enlightenment, 1974, p.179.

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

4. Philosophy and natural science. M., 1964, p.74-75; S.T. Melyuhin. Toward 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. Ways 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 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. The infinity of matter. M., 1965, p. 17-21; Omelyanovsky M

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All currently known elementary particles can be divided into groups according to their common properties and relation to interaction. There are four such interactions in nature: strong, electromagnetic, weak and gravitational.

Strong interaction has the highest intensity compared to other interactions. It determines the bonding of protons and neutrons in the nuclei of atoms (by exchanging virtual p-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 with the decays of μ, π, K-mesons and hyperons. It turned out that the weak interaction is universal in nature, all particles participate in it. The lifetime of most of these particles lies in the range 10 -8 - 10 -10 s, while the typical time of strong interactions is 10 -23 -10 -24 s. An illustration of such an interaction can be the fact that neutrinos capable of only weak interaction can freely pass through substance, 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 also increase significantly in the microcosm at distances of the order of 10 -33 cm, since the mass of generated particles increases. These interactions play a dominant role in the mega world.

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 on the energy in different ways; therefore, as the energy of interacting particles increases, 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: e, μ, τ, ν e, ν μ , ν τ - leptons participate in weak and electromagnetic interactions; II group make up 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 hypothesized that the structure of all hadrons includes objects that are exotic in their characteristics and are called quarks. It was assumed that there are three types of quarks u, d, s, the charges of which are fractional e u =+ 2 / z, ed = e s = - 1 / z of the electron charge, and the masses m u = m d ~ 300 MeV, ms ~ 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 / z of the electron charge. This quark is characterized by a new quantum number called charm.

In November 1974, a new J/ψ particle was discovered with unusual properties (the mass of 3.1 GeV is approximately three times the mass of the proton), the lifetime is ~10 -20 s (i.e., 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 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 mass of the c-quark predicted by the theory (m c ≈1.6 GeV). To finally confirm the existence of the c-quark, it is necessary hadrons with a clear “charm” were discovered.Phenomena indicating the birth of charmed particles have now been discovered.

Physicists believe that the existence of the c-quark has been 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 hadrons is of fundamental importance for confirming the validity of the entire quark hypothesis.

Theoretical physicists came to the conclusion that quarks of each type must be in one of three states, which are now usually characterized by three flowers(for example, yellow, blue, red); they suggest that the strong interaction of quarks is the interaction of their color with a new field, the so-called. gluon (from the English glue - glue, since this field "glues" the quarks in the hadron, as it were). Gluon field quanta - gluons- do not participate in electromagnetic and weak interactions. They not only change the color state of the quark, but also carry color themselves and interact with the gluon field. All this gave rise, by analogy with quantum electrodynamics, to 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 'escape' from hadrons.

There are special studies where the fundamental impossibility of the existence of quarks in a free state is proved.

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 symmetry principles. 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 observed, 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°-quanta of neutron fields, then the 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 validity of the Weinberg-Salam model. At present, the W ± and Z° particles have been discovered.

It is also 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. In 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. The existence of a new lepton (v τ - new neutrino) was also suggested, the τ-lepton has a new lepton quantum number, which was named sequolepton(from the English sequential - sequential).

Further research led to the conclusion that in order to restore symmetry, the number of quarks would have to be increased. Four was no longer enough to describe the objects of the microcosm, 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 ~10 GeV was discovered.

The discovery of these particles (they were called γ-mesons) brought to life the need for the existence of an even heavier quark "b" with an effective mass m b ~ 5 GeV with a new quantum number, called "beauty" (from English beauty).

The new γ mesons are particles with a hidden charm. Thus, the study of hadrons and leptons has enriched science with knowledge about new objects, about their quantitative and qualitative characteristics, and about their interactions. All this testifies to the advent of a new era in the study of the inexhaustible properties of micro-objects, which, together with various fields, constitute a fragment of an 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.

It has already been possible to create a unified electroweak interaction, encouraging results have been obtained in unifying the strong and electroweak interactions; moreover, the strong and weak interactions are in themselves its manifestation. The gravitational interaction still remains outside the unification, but there are already approaches to including it (supersymmetry) in the unified theory of interaction.

The modern development of elementary particle physics has made it possible to show that known particles (leptons, hadrons, quarks, gluons, photons) essentially determine the specifics of the processes of the microworld. To all appearances, 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 the theory already provides a rational explanation for a significant part of it. However, it is still significantly behind 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 attempts to construct a unified theory covering all particles and fields. There are two main trends here, ultimately related to each other. The first of them originates from the idea of ​​Louis de Broglie, which consists in putting the simplest wave function of the spinor type as a basis, describing a particle with a minimum non-vanishing angular momentum, i.e. spin S = 1/2 (in fractions of h / 2π) . Then, by combining these wave functions (eventually multiplying), under certain additional conditions, we obtain by a similar "merger" 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 momentum + 1 / 2 and + 1 / 2 , we get 1 (since spins + 1 / 2 can only orient themselves in parallel or antiparallel). Using the fusion method, it is possible, by combining two Dirac equations describing spin particles ("fermions"), to obtain the Klein-Gordon and Prok equations, and in the particular case of a vanishing rest mass, the Maxwell equations of electrodynamics. 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, Iordan, 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 electromagnetic field quanta. 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 creating a unified theory of elementary particles and fields, and not about the theory of matter, because the only theory of matter, as an objective reality that exists outside and independently of the cognizing subject, is dialectical materialism. If we take a unified spinor field as the basis of the new theory, then it can only interact with itself. This leads to the appearance of the so-called non-linear 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 ​​for particle masses and coupling constants, but it is undoubtedly one of the attempts worthy of attention, although it is not without flaws. This is only a research program that should not be overestimated, as has already been the case in separate articles published in our press.

It must be borne in mind that already several years ago the incorrectness of the mathematical interpretation of Heisenberg's spinor theory was revealed, and it was also shown that the indefinite metric introduced by Heisenberg leads to a violation of microcausality. There is good reason to believe that Heisenberg's concrete attempt to create a unified theory of elementary particles has so far failed, but the direction of research chosen by him should not be discounted. In recent years, a kind of return to the ideas of W. Heisenberg has been observed.

In 1958 in the USA, when Pauli was reporting on Heisenberg's theory, N. Bohr, who was present at the discussion, made a remark: "Heisenberg's theory is not crazy enough for a new theory" (crasy) (23, 20). N. Bohr meant the absence of an unusual, outlandish idea in this theory. 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 to be attempts to radically revise our space-time concepts as applied to ultrasmall 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 works of X. 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 coordinates that do not commute with each other, is discrete and at the same time isotropic. However, Snyder's ideas received almost no further development, with the exception of the works of Golfand and Kadyshevsky.

VG Kadyshevsky (50. 1961. 136. (1)) suggested introducing the universal length "l" into the theory of elementary particles on the basis of a change in the space-time geometry. He believed that the new geometry must 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) the non-invariance of the interval and the presence of a universal length would be the reasons for the non-conservation of parity;

c) there must be a subgroup for which S 2 is an invariant in order to be able to describe the symmetries of large regions of 4-space - large compared to the elementary length "l". The author associates the length "l" with the value C - the universal constant of weak interaction. After extracting the multipliers " 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 X. Koisch and the Soviet physicist I. S. Shapiro in their studies considered a discrete space consisting of a finite number of elements, and showed a good agreement between a number of conclusions and experimental data. This is also one of the possible search ways, bringing closer to the creation of a systematics of elementary particles, to a new generalizing physical theory. However, I. S. Shapiro, speaking in 1962 at the Meeting on philosophical problems physicists of elementary particles, assessed his work as an initial stage, very distant from the creation of a theory that allows comparison with experience. A philosophical analysis of this problem was given by R. A. Aronov (31.1957.3).

In physics, questions about the so-called spectral representations and dispersion relations were considered. According to 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 studied as they continued from real values ​​into the complex region. The application of the theory of functions of a complex variable to these quantities yielded extremely important results. Mandelstam (99) introduced double dispersion relations, considering the complex values ​​of not only the energy, but also the momentum. Regge proposed a generalization of the S-matrix formalism and dispersion relations to complex values ​​of the angular momentum. As a result of the application of "registry", the ratios between the amplitudes of the probabilities of various scattering processes were determined: ππ, πN, NN, etc. at high energies. However, there are data (in the field of ultrahigh-energy physics) that limit the Regists' claims to the comprehensiveness of their ideas.

Academician I. Tamm considered the dispersion theory to a certain extent phenomenological, since, without going into the mechanism of elementary physical phenomena, it extracts from 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 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 successes of the dispersion theory (both present and future) by no means 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 confirmed these assumptions. There were many other attempts to construct a theory of elementary particles. Let's briefly analyze some of them.

Fermi and Yang proposed to consider the p-meson as being formed from a nucleon and an antinucleon with the help of some still unknown forces acting at extremely small distances p+¯p = π. The huge potential energy of binding "eats" almost the entire mass of both nucleons, leaving only the mass of the pion. S. Sakata's proposal aroused interest. He based the theory on p, π, λ and three corresponding antiparticles. Then, by combining these basic particles, one can obtain all pions, K-mesons and hyperons. “This model,” wrote S. Sakata, “attracted attention, since it not only served as a “substantial” basis for the structure of the strong interaction, but also made it possible to explain the mass spectrum of compound particles and predicted the existence of resonance particles that were being discovered at that time” (74, 168). However, the nature of the cohesive forces remained unclear. At least three basic particles are needed to ensure the presence of such fundamental properties as charge, isospin, strangeness (represented by the λ-hyperon). Again, it is clear that "rotating" spinor particles, fermions, should be taken as the basis, since in the absence of "rotation" there would be nowhere to obtain 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 ethereal 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 collectively forming nature. My point of view is based on the provisions of the materialistic dialectics ... it is necessary first of all to establish whether the more than thirty types of elementary particles discovered so far 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 as well. The leptons e - , v, μ and some "baryon" field B (the so-called B-matter) are taken as a basis. By combining one of the leptons with the field B, 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 about symmetry "Kyiv symmetry", since they were born at the symposiums of the Kyiv 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 triples of baryons (p, π, λ) and leptons (v, e - , μ -). Any term of the four-fermion interaction, involving the operators of these particles, can be contrasted with a similar term obtained from the first by replacing λ with μ - , π with e - , p with v. Then, if the process is allowed/forbidden before the replacement, then it remains allowed/forbidden after the replacement of one particle from the baryon/lepton triad by the "symmetrofactor" from the lepton/baryon triad. 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 has become possible to interpret the Kyiv symmetry as a correspondence of four quarks - u, c, d, s to four leptons - v e, 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 of a temporary, transitory nature. Further theoretical and experimental penetration into the depths of the microworld and ever broader studies of phenomena in space, inevitably violating any single picture, will lead to its disintegration into separate elements, until the tendency to unify again at a higher level arises.

The introduction of various concepts reflecting the real properties of particles (isotopic spin, strangeness, baryon charge, etc.) brought us closer to the correct classification of particles. A huge role in the classification of microparticles belongs to the principle of symmetry. It is easy to see that the 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 further presentation.

J. Chu, M. Gell-Mann, and I. Ne'eman (21, 5E) proposed a new classification of strongly interacting particles of matter, in which the division of particles into elementary and complex (composite) loses its meaning. These authors proposed to consider particles combined into groups (supermultiplets) so that particles with different rest masses 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, with equal justification, be considered 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 on the use of the so-called Regge trajectories, i.e. curves relating the mass of a particle to its internal angular momentum (spin) in each group.

Many physicists now believe that the Gell-Mann octet scheme is the most successful. It is based on the principle SU(3) symmetry. The eight known baryons are considered as a supermultiplet corresponding to higher symmetry; this symmetry is broken, and the supermultiplet splits into isotopic spin multiplets. Strongly interacting particles are described in a "unitary spin" space that has eight components: the first three are isospin components, the next four play the role of strangeness-changing operators, and the last is proportional to the hypercharge. When the higher symmetry ("unitary") is violated, isospin and hypercharge are preserved, while 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 combine strongly interacting particles according to a coherent scheme and at the same time reflect their specificity (asymmetry of properties). The Gell-Mann octet scheme once again demonstrates the enormous heuristic power of the symmetry principle. Within the framework of the "eight-fold path" hypothesis, the existence of the Ω-hyperon, which was discovered at the Brookhaven accelerator in the USA, was predicted on the basis of symmetry concepts and conservation laws (214). At one time, we wrote that the successes to which the unitary symmetry property was taken into account in the theory give hope that experimental studies will lead to the discovery of other particles with a fractional electric charge predicted by the theory (± 1 / s and ± 2 / s 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 microcosms 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, and the other ten times greater. The maximons introduced in this way are 1019 times larger in mass than 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. They fall to the center of the planet under the influence of gravity... on accelerators of the distant future are excluded" (53.1966.51, 878).

An 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 microparticles they introduce new characteristics of the properties of material micro-objects and fields. Such a difference in approaches to solving the same problem is quite justified.

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Penetration into the depths of the microworld is associated with the transition from the level of atoms to the level of elementary particles. As the first elementary particle at the end of the nineteenth century. the electron was discovered, and then in the first decade of the twentieth century - the photon, proton, positron and neutron. After the Second World War, thanks to the use of modern experimental technology, and above all, powerful accelerators, in which conditions of high energies and enormous speeds are created, the existence of a large number of elementary particles - over 300 was established. Among them are both experimentally discovered and theoretically calculated, including resonances, quarks and virtual particles.

The term "elementary particle" originally meant the simplest, then indecomposable particles that underlie any material formations. Later, physicists realized the whole conventionality of the term "elementary" in relation to micro-objects. Now there is no doubt that the particles have a complex structure, but the historically established name continues to exist.

The main characteristics of elementary particles are: mass, charge, mean lifetime, spin and quantum numbers. Rest mass of elementary particles determined with respect to the rest mass of the electron. There are elementary particles that do not have a rest mass - photons. The rest of the particles on this basis are divided into leptons – light particles(electron, muon, neutrino); mesons – medium particles with a mass ranging from one to a thousand masses of an electron (p-mesons, K - mesons); baryons – heavy particles whose mass exceeds a thousand masses of an electron (protons, neutrons, hyperons and many resonances).

Electric charge is another important characteristic of elementary particles. All known particles have a positive, negative, or zero charge. Each particle, except for a photon and two mesons, corresponds to antiparticles with the opposite charge. In 1964 scientists put forward the idea quarks, those. particles having fractional charges, of which all elementary particles are composed. This hypothesis has become widespread in the scientific world, although it has not yet found a final experimental confirmation.

By particle lifetime are divided into stable and unstable. There are five stable particles: photon, two varieties of neutrino, electron, and proton. It is stable particles that play the most important role in the structure of macrobodies. All other particles are unstable, they exist for about 10 -10 - 10 -24 s, after which they decay. Elementary particles with an average lifetime of 10 -23 - 10 -24 s are called resonances. Due to their short lifetime, they decay before they even leave the atom or atomic nucleus. The resonant states have been calculated theoretically; it is not possible to fix them in real experiments.

In addition to charge, mass and lifetime, elementary particles are also described by concepts that have no analogues in classical physics: the concept "back", or own angular momentum of a microparticle, and concept "quantum numbers" expressing the state of elementary particles.

In the characterization of elementary particles, there is another important idea - interaction. There are four types of fundamental interactions in nature: strong, electromagnetic, weak and gravitational. The properties of elementary particles are determined mainly by the first three types of interaction.

Strong interaction occurs at the level of atomic nuclei and represents the mutual attraction and repulsion of their constituent parts. It acts at a distance of about 10 -13 cm. Under certain conditions, strong interaction binds particles very strongly, as a result of which material systems with high binding energy are formed - atomic nuclei. It is for this reason that the nuclei of atoms are stable and difficult to destroy.

Electromagnetic interaction about a thousand times weaker than a strong one, but much more long-range. The carrier of electromagnetic interaction is not having a charge photon is the quantum of the electromagnetic field. In the process of electromagnetic interaction, electrons and atomic nuclei are combined into atoms, atoms into molecules. This interaction is fundamental in chemistry and biology.

Weak interaction possible between different particles at a distance of 10 -15 - 10 -22 cm and is associated mainly with the decay of particles. According to the current level of knowledge, most particles are unstable due to the weak interaction.

Gravitational interaction is the weakest, not taken into account in the theory of elementary particles. However, at ultra-small distances (of the order of 10 -33 cm) and at ultra-high energies, gravity again becomes essential. On a cosmic scale, gravitational interaction (gravitation) is crucial. Its range is not limited.

In nature, as a rule, not one, but several types of interaction are manifested simultaneously, and the properties of many particles are determined by all four types. Fundamental interactions lead to the transformation of particles: their destruction and creation. The time during which the transformation of elementary particles takes place depends on the force of interaction. Therefore, according to the time of various transformations, one can judge the strength of the interactions associated with them. Interactions of elementary particles are carried out by means of the corresponding physical fields, of which they are quanta.

In modern quantum field theory, a field is understood as a system with a variable number of particles (field quanta). The lowest energy state of the field, in which there are no field quanta at all, is called vacuum. In a vacuum state, in the absence of excitation, the electromagnetic field does not contain particles (photons). In this state, it does not possess the mechanical properties inherent in corpuscular matter. Vacuum does not contain ordinary types of matter, but it is not empty in the literal sense of the word, since with appropriate excitation, photons appear in it - quanta of the electromagnetic field, through which electromagnetic interaction is carried out. There are other physical fields in the vacuum, in particular, the gravitational one, the quanta of which, gravitons, predicted theoretically, but experimentally not fixed yet.

The main problem of quantum field theory is the problem of the interaction of particles of different types. So far, it has been solved only in Kantian electrodynamics, which describes the interaction of electrons, positrons, and photons. Quantum field theory for strong and weak interactions has not yet been developed. They are described by means of non-rigorous methods, although it is clear that without an appropriate theory it is impossible to understand the structure of elementary particles, which is determined precisely by their interaction. Therefore, the question of the structure of elementary particles has not been finally resolved. According to modern ideas, the structure of elementary particles is described by means of continuously emerging and again decaying "virtual" particles. The formal involvement of virtual particles means that the internal structure of elementary particles cannot be described through other particles.

The most important direction in the development of modern physics is the so-called "Great Union"- an attempt to reduce all four types physical interaction(strong, weak, gravitational and electromagnetic) to one fundamental interaction, which would explain the physical form of the motion of matter in general and create the most fundamental physical theory. Many scientists believe that such a theory can only be created by taking into account cosmological circumstances, by studying situations where the microcosm is connected with the megaworld, the ultrasmall with the ultralarge, physics with astronomy and cosmology.

Federal State Educational Institution

higher professional education

"SOUTH FEDERAL UNIVERSITY"

Faculty of Economics

Elementary particles.

Their classification and main properties.

Performed

1st year student of group 11

Bublikova Ekaterina

Rostov-on-Don - 2009

Introduction. World of elementary particles.

Fundamental physical interactions.

1. Gravity.

   Electromagnetic interaction.

   Weak interaction.

   Strong interaction.

Classification of elementary particles.

1. Characteristics of subatomic particles.

   The history of the discovery of elementary particles.

2.5. Theory of quarks.

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… Great unification.

List of used literature.

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 are occupied with the study of 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 really elementary. Elementary particles in the exact meaning of this term are primary, further indecomposable particles, of which, by assumption, all matter consists, 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 revolving around the nuclei. But there are also particles that practically do not occur in the matter surrounding us. If the average lifetime of a neutron outside the atomic nucleus is 15 minutes, then the lifetime of such short-lived particles is extremely short, it is the smallest fraction of a second. After this extremely short time, they decay into ordinary particles. There are astonishingly many such unstable short-lived particles: several hundred of them are already known. However, one cannot assume 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 in the study of nuclear processes, therefore, until the middle of the 20th century, elementary particle physics was a branch of nuclear physics. At present, elementary particle physics and nuclear physics are close, but independent branches of physics, united by the commonality of many of the 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 bewildered by the abundance, variety, and unusualness of newly discovered subatomic particles. There seemed to be no end to them. It is completely incomprehensible why 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 the following decades showed that there is no doubt about the existence of such a structure. At the end of the 20th century, physics begins to understand the significance of each of the elementary particles.

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

1. Fundamental physical interactions.

In your Everyday life a person is faced with many forces acting on bodies. Here is the force of the wind or the oncoming flow of water, air pressure, a powerful release of exploding chemicals, the muscular strength of a person, the weight of heavy objects, the pressure of light quanta, the attraction and repulsion of electric charges, seismic waves, sometimes causing catastrophic destruction, and volcanic eruptions, leading 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 a great variety, 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 ability to different 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 (gravitation) has become the first of the four fundamental interactions the subject of scientific research. After the appearance in the seventeenth century. Newtonian 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 small intensity. The magnitude of the gravitational interaction between the components of the hydrogen atom is 10n, where n = -39, from the strength of the interaction of electric charges. It may seem surprising that we can feel gravity at all, since it is so weak. How can it be 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. Because every particle of matter exerts a gravitational pull, gravity increases as more and more clumps of matter form. We feel gravity in everyday life because all the Earth's atoms together pull us together. And although the effect of the gravitational attraction of one atom is negligible, but the resulting force of attraction from all atoms can be significant.

Gravity - far-reaching force of nature. This means that although the intensity of the gravitational interaction decreases with distance, it propagates in space and can affect bodies very distant from the source. On an astronomical scale, the gravitational interaction, as a rule, plays a major role. Thanks to long-range action, gravity does not allow the Universe to fall apart: it keeps planets in orbits, stars in galaxies, galaxies in clusters, clusters in the Metagalaxy.

The force of gravity acting between particles is always an attractive force: it tends to bring the particles closer together. Gravitational repulsion has never been observed (although in the traditions of quasi-scientific mythology there is a whole area called levitation - the search for "facts" of antigravity). Since the energy stored in any particle is always positive and endows it with a 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 unambiguous answer to this question. There are different opinions and concepts of physicists in this regard.

1.2. Electromagnetic interaction.

The electrical forces are much larger than the gravitational ones. In contrast to the weak gravitational force, electrical forces acting between bodies of ordinary size can be easily observed. Electromagnetism has been known to people since time immemorial (polar lights, 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.K. Maxwell, who combined electricity and magnetism in a unified theory of electromagnetism - the first unified field theory.

The existence of the electron was firmly established in the 1990s. 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 an electromagnetic field, or field quanta - photons.

Like electric charges, magnetic poles of the same name repel, and opposite magnetic poles attract. However, unlike electric charges, magnetic poles do not occur separately, but only in pairs - the north pole and South Pole. Since ancient times, there have been attempts 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 the existence of a monopole.

Like electrical and gravitational interactions, the interaction of magnetic poles obeys the inverse square law. Consequently, the electric and magnetic forces are "long-range", and their action is perceptible at great distances from the source. Thus, the Earth's magnetic field extends far into outer space. The powerful magnetic field of the Sun 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 progressed slowly towards revealing the existence of the weak interaction. The weak force is responsible for the decay of particles, and therefore its manifestation was faced with the discovery of radioactivity and the study of beta decay.

Beta decay exhibited a highly bizarre feature. Studies 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, V. Pauli suggested that together with the electron during beta decay, another particle flies out. She is neutral and has an unusually high penetrating power, as a result of which she 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 leptons. They participate only in weak and gravitational interactions and therefore interact extremely weakly with matter. A distinction is made between an electron neutrino, which always pairs with an electron or a positron, a muon neutrino, which pairs with a muon, and a tau neutrino, associated with a heavy lepton. Each type of neutrino has its own antiparticle, which differs from the neutrino 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 are right-handed (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 the neutrino, but there remained a lot of mystery. The fact is that both electrons and neutrinos were emitted by unstable nuclei. But it has been irrefutably proven that there are no such particles inside nuclei. How did they arise? It has been suggested that electrons and neutrinos do not exist in the nucleus "ready-made", but are somehow formed from the energy of the radioactive nucleus. Further studies showed that the neutrons that make up the nucleus, left to themselves, after a few minutes decay into a proton, an electron and a neutrino, i.e. instead of one particle, three new ones appear. The analysis led to the conclusion that known forces cannot cause such a disintegration. He, apparently, was generated by some other, unknown force. Studies have shown that this force corresponds to some weak interaction.

It is much weaker than electromagnetic, although stronger than gravitational. It spreads over very small distances. The radius of the weak interaction is very small and is about 2*10^(-16)cm. 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 for the photon, participate in the weak interaction. It causes most of the decays of elementary particles, the interaction of neutrinos with matter, etc. The weak interaction is characterized by violation of parity, strangeness, "charm". A unified theory of the weak and electromagnetic interactions was created at the end of the 1960s by S. Weinberg, S. Glashow, and A. Salam. It describes the interactions of quarks and leptons through the exchange of four particles: massless photons (electromagnetic interaction) and heavy intermediate vector bosons - W+, W- and Z° particles, which are carriers of the weak interaction (experimentally discovered in 1983). This unified interaction came to be called electroweak. Since Maxwell's construction of the theory of the electromagnetic field, the creation of this theory has been 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 characteristic example of the energy released by the strong force is our Sun. In the depths of the Sun and stars, starting from a certain time, thermonuclear reactions are continuously occurring, caused by strong interaction. But man has also learned to release the strong interaction: a hydrogen bomb has been created, and technologies for controlled thermonuclear reaction have been designed and are being improved.

Physics came to the idea of ​​the existence of a strong interaction in the course of studying the structure of the atomic nucleus. Some force must hold the protons in the nucleus, preventing them from flying apart under the influence of electrostatic repulsion. Gravity is too weak for that; 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 core. The radius of action of the new force turned out to be very small. The strong force drops sharply at a distance from the proton or neutron exceeding about 10^(-15) m.

In addition, it turned out that not all particles experience strong interaction. 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 one by about 100 times. The theoretical explanation of the nature of the strong interaction has been difficult to develop. A breakthrough was outlined in the early 1960s, 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 traced. On the one hand, there are interactions of an unlimited range of action (gravity, electromagnetism), and on the other hand, interactions of a small radius of action (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 microcosm and long-range action in the entire Universe.

1.5. The problem of the unity of physics.

Cognition is a generalization of reality, and therefore the goal of science is the search for unity in nature, the linking of disparate fragments of knowledge into a single picture. In order to create a unified system, it is necessary to open a link between different branches of knowledge, some fundamental relationship. The search for such links 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 cognition 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 directs scientific research along new, unbeaten roads. The discovery by Newton of the connection between the attraction of bodies under terrestrial conditions and the movement of the planets marked the birth of classical mechanics, on the basis of which the technological base of modern civilization was built. The establishment of a connection between the thermodynamic properties of a gas and the chaotic motion of molecules placed the atomic-molecular theory of matter on a solid foundation. In the middle of the last century, Maxwell created a unified electromagnetic theory that embraced both electrical and magnetic phenomena. Then, in the 1920s, Einstein made attempts to combine electromagnetism and gravity in a single theory.

But by the middle of the 20th 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 pass.

There is a point of view that all four (or at least three) interactions are phenomena of the same nature and their unified theoretical description should 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 very uncertain.

However, in the second half of the 20th century, the preconditions for the realization of this dream appeared and the confidence that this is not a matter of the distant future. It looks like it could very well become a reality soon. The decisive step towards a unified theory was taken in the 1960s and 1970s with the creation first of the theory of quarks and then of the theory of the electroweak interaction. There is reason to believe that we are on the verge of a more powerful and deeper unification than ever before. There is a growing conviction 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 19th-20th 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. Identification in the future of the presence of constituent constituents of atoms - electrons and nuclei, the 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 assert 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. It is possible 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 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 verification of 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 talking 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 masses. 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 greater than the mass of an electron.

The electric charge varies in a rather narrow range and is always a multiple of the fundamental unit of charge - the electron charge (-1). Some particles, such as photons and neutrinos, have no charge at all.

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

The micro-objects of the first group are able to “populate” the same state in an unlimited number, and the higher the number, the stronger this state is “populated”. Such micro-objects are said to obey Bose-Einstein statistics. For brevity, they are simply called bosons. Micro-objects of the second group can “populate” states only one by one. And if the considered state is occupied, then no micro-object of this type can get into it. Such micro-objects are said to obey the 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.

The particles are also characterized by their lifetime. On this basis, the particles are divided into stable and unstable. The 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 varies from a few microseconds to 10n sec (where n = -23). This means that when this time expires, they spontaneously, without any external influences, decay, 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 specified decay of one or another specific neutron will occur, because each specific act of decay is random. Each unstable elementary particle is characterized by its 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 pass into the ground or less excited state.

Instability determined by probabilistic laws is, along with the presence of spin, the second purely specific property inherent in micro-objects. It can also be considered as an indication of some "internal complexity" of the micro-object.

However, instability is a specific, but by no means an obligatory property of a micro-object. Along with unstable, 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 marked with the letter L. For leptons it is equal to +1, and for antileptons -1. Distinguish: electronic lepton charge, which only electrons, positrons, electronic neutrinos and antineutrinos possess; muon lepton charge, which only muons and muon neutrinos and antineutrinos possess; lepton charge of heavy leptons and their neutrinos. The algebraic sum of the lepton charge of each type is conserved with very high accuracy in all interactions.

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

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

"Charm" (charm) - a quantum number that characterizes 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 - a unit of measurement of the magnetic moment in the physics of the atom, atomic nucleus and elementary particles. The magnetic moment due to 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 the function does not change sign during such a transformation, 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 preserved in all interactions except the weak one.

Charge parity - 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 the weak one.

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

2.2. The history of the discovery of elementary particles.

The notion that the world is made up 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 the surrounding objects was expressed 400 years before our era by the Greek philosopher Democritus. He called these particles atoms, that is, indivisible particles. Science began to use the concept of atoms only in early XIX 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 around 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 in 1896 discovered the phenomenon of radioactivity.

This was followed by the discovery of the first elementary particle by the English physicist Thomson in 1897. It was an electron that finally acquired the status of a real physical object and became the first known elementary particle in the history of mankind. Its mass is about 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.

An analysis of the atomic spectra shows that the spin of an electron is 1/2, and its magnetic moment is equal to one Bohr magneton. Electrons obey Fermi statistics because they have a half-integer spin. This agrees with experimental data on the structure of atoms and on 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 - the first). This elementary particle was discovered in 1919 by Rutherford while studying the fission products of atomic nuclei of various chemical elements. In a literal sense, a proton is the nucleus of an atom of the lightest isotope of hydrogen - protium. The proton spin is 1/2. The proton has a positive elementary charge +e. Its mass is:

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

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

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

The conclusion about the existence of an electromagnetic field particle - a photon - originates from the work of M. Planck (1900). Assuming that the energy of the electromagnetic radiation of an absolutely black body is quantized (that is, it 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 stream of individual quanta (photons), and on this basis explained the laws of the photoelectric effect. Direct experimental proof of the existence of the photon was given by R. Millikan in 1912-1915 and by A. Compton in 1922.

The discovery of the neutrino, a particle that hardly interacts with matter, originates from the theoretical conjecture of W. Pauli in 1930, which made it possible, by assuming the birth of such a particle, to eliminate difficulties with the law of conservation of energy in the processes of beta decay of radioactive nuclei. The existence of neutrinos was experimentally confirmed only in 1953 by F. Reines and K. Cowen.

But the substance consists not only of 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 signs of electric charge and magnetic moment, baryon charge, lepton charge, strangeness and etc. All elementary particles, except for absolutely neutral ones, have their own antiparticles.

The first discovered antiparticle was the positron (from Latin positivus - positive) - a particle with an electron mass, but a positive electric charge. This antiparticle was discovered in cosmic rays by the 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. Pair annihilation itself is one of the types of transformations of elementary particles that occurs when a particle collides with an antiparticle. During annihilation, the particle and 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 pair. The positron itself is stable, but in matter, due to annihilation with electrons, there is a very short time. The annihilation of an electron and a positron is that when they meet, they disappear, turning into γ- quanta (photons). And in the event of a collision γ- a quantum with some massive nucleus, an electron-positron pair is born.

In 1955, another antiparticle was discovered - the antiproton, and a little later - the antineutron. The antineutron, like the neutron, does not have an electric charge, but it undoubtedly belongs to the 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. Atoms of antimatter should be built in such a 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 has received brilliant experimental confirmation. In 1969, at the proton accelerator in the city of Serpukhov, Soviet physicists obtained the 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.

An important role in the physics of elementary particles is played by conservation laws that establish equality between certain combinations of quantities that characterize the initial and final state of the system. The arsenal of conservation laws in quantum physics is greater than in classical physics. It was supplemented by the laws of conservation of various parities (spatial, charge), charges (lepton, baryon, etc.), internal symmetries inherent in one or another type of interaction.

Identification of the characteristics of individual subatomic particles is an important, but only the initial stage in the knowledge of their world. At the next stage, it is still necessary to understand what is the role of each individual particle, what are its functions 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 a strong interaction. The particles participating in the strong interaction form a special class and are called hadrons. Particles that participate in the weak interaction and do not participate in the strong one are called leptons. In addition, there are interaction-carrier particles.

2.3. Leptons.

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

Another well-known lepton is the neutrino. Neutrinos are the most common particles in 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 a prevalence of neutrinos, it is very difficult to study them. As we have noted, neutrinos are almost elusive. Not participating in either strong or electromagnetic interactions, they penetrate matter as if it does not exist at all. Neutrinos are some "ghosts of the physical world".

Muons are fairly widespread in nature, accounting for a significant portion of cosmic radiation. In many ways, 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, a muon decays into an electron and two neutrinos. At the end of the 1970s, a third charged lepton was discovered, which was 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 1960s, the list of leptons expanded significantly. It was found that there are several types of neutrinos: electron neutrino, muon neutrino and tau neutrino. 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 distinct leptons is twelve. Neutral leptons participate only in the weak interaction; charged - in the weak and electromagnetic. All leptons participate in gravitational interaction, 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 the hadrons, the neutron and proton are the most well-known and widespread, which in turn belong to the class of nucleons. The remaining hadrons are short-lived and rapidly decay. 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 an electron, but less than the mass of a proton. These particles predicted by quantum theory were later called mesons. Mesons were discovered experimentally. They turned out to be a whole family. All of them turned out to be short-lived unstable particles living in a free state in 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, in studies at charged particle accelerators, particles with masses exceeding the mass of a proton were discovered. These particles were called hyperons. They were found even more than mesons. The family of hyperons includes: lambda-, sigma-, xy- and omega-minus-hyperons.

The existence and properties of most of the known hadrons have been established in experiments on accelerators. The discovery of many different hadrons in the 1950s and 1960s puzzled physicists extremely. But over time, hadrons were classified according to their mass, charge, and spin. Gradually, a more or less clear picture began to emerge. Concrete ideas appeared on how to systematize the chaos of empirical data, how to solve the mystery of hadrons in scientific theory. The decisive step here was taken in 1963, when the theory of quarks was proposed.

2.5. Theory of quarks.

The theory of quarks is the theory of the structure of hadrons. The basic idea of ​​this theory is very simple. All hadrons are built from 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 that 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 equal to zero or one. All quarks have spin S, so they are fermions. The founders of the theory of quarks Gell-Mann and Zweig, in order to take into account all hadrons known in the 60s, introduced three types (colors) of quarks: u (from up - top), d (from down - bottom) 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. Comparatively heavy particles - baryons - are composed 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 is made up of two u-quarks and one d-quark (uud), while a neutron is made up of two d-quarks and one u-quark (udd). In order for this "trio" of quarks not to decay, a force holding them, a kind of "glue", is needed.

It turned out that the resulting interaction between neutrons and protons in the nucleus is simply a residual effect of a more powerful interaction between the quarks themselves. This explained why the strong force seems so complicated. When a proton "sticks" to a neutron or another proton, six quarks are involved in the interaction, each of which interacts with all the others. A significant part of the forces is spent on strong gluing of a trio of quarks, and a small part is spent on bonding two trios of quarks to each other. But later it turned out that quarks also participate in the weak interaction. The weak force 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 can be obtained from various combinations of the three basic particles was a triumph for the theory of quarks. But in the 1970s, new hadrons were discovered (psi-particles, upsilon meson, etc.). This dealt a blow to the first version of the theory of quarks, since there was no 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 got the name - c - quark (charm - charm), b - quark (from bottom - bottom, and more often beauty - beauty, or charm), and subsequently another color was introduced - t (from top - top).

So far, free quarks and antiquarks have not been observed. However, there is practically no doubt about the reality of their existence. Moreover, searches are underway for "real" elementary particles following quarks - gluons, which are carriers of interactions between quarks, because quarks are held together by a strong interaction, and gluons (color charges) are carriers of the strong interaction. The field of elementary particle physics that studies the interaction of quarks and gluons is called quantum chromodynamics. As quantum electrodynamics is the theory of electromagnetic interaction, so 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 by exchanging 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 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 - from a quark and an antiquark.

Although there is some dissatisfaction with the quark scheme, most physicists consider quarks to be truly elementary particles - pointlike, 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 (excluding carriers of fundamental interactions) at the end of the 20th 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 exhausted by 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 does not allow the world to fall apart. Such particles are called carriers of interactions, and a separate kind of particles transfer their interactions.

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

The theory of electromagnetic interaction was represented 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 a quantum characteristic of "color". Gluons are carriers of interaction between quarks, because connect 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.

An opinion is expressed 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 gravitational field quantum having zero rest mass, zero electric charge and spin 2. In principle, gravitons can be fixed in an experiment. But since the gravitational interaction is very weak and practically does not manifest itself in quantum processes, it is very difficult to directly fix gravitons, and so far no scientist has succeeded in this.

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 a 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 the laws of motion of microparticles in given external fields. It allows one to describe the motion 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 divisions 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 the chemical bond, explain the periodic system of elements, etc. Since the properties of macroscopic bodies are determined by the motion and interaction of the particles that form them, the laws of quantum mechanics underlie the understanding of most macroscopic phenomena. Thus, quantum mechanics has made it possible to understand many of the properties solids, explain the phenomena of superconductivity, ferromagnetism, superfluidity, and much more. Quantum-mechanical laws underlie nuclear energy, quantum electronics, etc. Unlike the classical theory, all particles act in quantum mechanics as carriers of both corpuscular and wave properties, which are not exclude, but complement each other. The wave nature of electrons, protons and other particles has been 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 this 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, the angular momentum and its projection onto an arbitrary direction, etc.; in the classical theory all these quantities can change only continuously. A fundamental role in quantum mechanics is played by Planck's constant ћ - one of the main scales of nature, delimiting the areas of phenomena that can be described by classical physics, from the 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 - it 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 mutual transformations. The need for such a theory is generated by quantum-wave dualism, the existence of wave properties in all particles. In quantum field theory, the interaction is presented as the 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 - statistical physics of quantum systems consisting of a large number of particles. For particles with an integer spin, this is the Bose Einstein statistics; for particles with a half-integer, the Fermi Dirac statistics.

In the middle of the twentieth century, a theory of electromagnetic interaction was created - quantum electrodynamics of QED - this is a theory of interaction of photons and electrons, thought out to the smallest detail and equipped with a perfect mathematical apparatus. QED is based on the 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 creates a (virtual) electron-positron pair that can annihilate to form a new photon. The latter can be absorbed by the original photon, but it can give rise to a new pair, and so on. 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 move in space along not quite definite trajectories. It is still possible to determine in one way or another the starting and ending points of the path - before and after scattering, but the path itself in the interval between the beginning and the end of the movement remains undefined.

The description of the interaction with the help of a carrier particle led to an extension of the concept of a photon. The concepts of a real (a quantum of light visible to us) and a virtual (transient, ghostly) photon are introduced, which are "seen" only by charged particles undergoing scattering.

To test whether the theory agrees with reality, physicists focused on two effects 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 an extremely small correction to the electron's own magnetic moment. Theoretical and experimental results of QED verification coincide with the highest accuracy - more than nine decimal places. Such a striking correspondence gives the right to consider QED as the most perfect of the existing natural science theories.

After a similar triumph, QED was adopted as the model for the quantum description of three other fundamental interactions. Of course, the 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 took place in natural science: two fundamental interactions out of four were combined into one by physics. The picture of the fundamental foundations of nature has become somewhat simplified. Electromagnetic and weak interactions, seemingly very different in nature, actually turned out to be two varieties of a single electroweak interaction. The theory of the electroweak interaction decisively influenced the further development of elementary particle physics at the end of the 20th century.

The main idea in constructing this theory was to describe the weak interaction in terms of the gauge field concept, 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 20th 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 through any angle from its center. The laws of electricity are symmetrical with respect to the replacement of positive charges by negative ones and vice versa. Thus, by symmetry we mean invariance with respect to some operation.

There are different types of symmetries: geometric, mirror, non-geometric. Among non-geometric ones there are so-called gauge symmetries. Gauge symmetries are abstract and are not fixed directly. 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, the 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. 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 viewed as a means by which nature creates its inherent local gauges. symmetry. The significance of the concept of gauge symmetry lies in the fact that, thanks to it, all four fundamental interactions that occur in nature are theoretically modeled. 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 - the field of weak forces. Weakly interacting particles, such as electrons and neutrinos, carry a "weak charge" that is analogous to an electric charge and associates these particles with 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 complicated than the electromagnetic one. After all, the very mechanism of this interaction is more complex. First, in the decay of a neutron, for example, particles of at least four different types (neutron, proton, electron, and neutrino) participate in the weak interaction. Secondly, the action of weak forces leads to a change in their nature (the transformation of some particles into others due to the weak interaction). On the contrary, the 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 three new force fields are needed to maintain symmetry here, in contrast to a single electromagnetic field. A quantum description of these three fields was also obtained: there must be three new types of particles - interaction carriers, one for each field. Together they are called heavy vector bosons with spin 1 and are carriers of the weak interaction.

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

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

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

Differences in the properties of electromagnetic and weak interactions theory is explained by the violation of 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 has such a small value because the W and Z particles are very massive. Leptons rarely approach such small distances (r 10n see, 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 is carried out just as easily as the exchange of photons (massless particles). The difference between photons and bosons is erased. Under these conditions, there should be a complete symmetry between the electromagnetic and weak interactions - the electroweak interaction.

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

3.3. Quantum chromodynamics.

The next step on the path of the Grand Unification of fundamental interactions is the merging of the strong interaction with the electroweak one. 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 bonding of quarks (in pairs or triplets) into hadrons.

The idea here is the following. 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 the usual color). If the electromagnetic field is generated by only one kind of charge, then three different color charges were required to create a more complex gluon field. Each quark is "coloured" in one of three possible colors, which, quite arbitrarily, have been called red, green, and blue. And accordingly, antiquarks are anti-red, anti-green and anti-blue.

At the next stage, the theory of the strong interaction develops along the same lines as the theory of the weak interaction. The requirement of local gauge symmetry (ie 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 particles-carriers of these fields are gluons, and thus it follows from the theory that there should 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 are constantly exchanging gluons, changing their color. However, such changes are not arbitrary, but obey a strict rule: at any moment in time, the "total" color of the three quarks must be white light, i.e. 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: the preservation of the white color of all hadrons while changing the color of their constituent parts. Quantum chromodynamics perfectly explains the rules that all combinations of quarks obey, the interaction of gluons with each other, the complex structure of a hadron consisting of quarks "clothed" in clouds, etc.

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

3.4. On the way to... Great unification.

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

The experience of successful unification of 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, 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 unification energy. 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 1970s and 1990s, several competing Grand Unification theories were developed. They are all based on the same idea. If the electroweak and strong forces are really only two sides of the great unified force, then the latter must also have a corresponding gauge field with some complex symmetry. It (symmetry) should be sufficiently general, capable of covering all gauge symmetries contained in both quantum chromodynamics and the theory of the electroweak interaction. Finding such a symmetry is the main task on the way to creating a unified theory of strong and electroweak interactions. There are different approaches that give rise to competing versions of the Grand Unification theories.

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

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

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

On the basis of the Grand Unification theories, at least two important regularities have been predicted that can and should be verified experimentally: the instability of the proton and the existence of magnetic monopoles. Experimental detection of proton decay and magnetic monopoles could be a strong argument in favor of the Grand Unification theories. The efforts of experimenters are aimed at verifying these predictions. However, there are still no firmly established experimental data on this subject. The point is that Grand Unified Theories deal with particle energies above 10n GeV, where n = 14. This is a 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 X and Y bosons. And therefore the main field of application and testing of the theories of the Grand Unification 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 is under such conditions that superheavy particles could be born and annihilate.

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

Bibliography.

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