Particles antiparticles and their properties. War of particles and antiparticles. The history of the discovery of antiparticles

ANTIPARTICLES

The set of elements. particles having the same values of masses and other physical. char-k, as their "twins" - h-tsy, but differing from them in the sign of certain char-k effects (for example, electric charge, magnetic moment). The name "h-tsa" and "A." to a certain extent conditional: one could call the antielectron (positively charged. e-n) h-tsey, and e-n - A. However, the atoms in the islands in the observable part of the Universe contain e-ns with a negative. charge, while protons are positive. Therefore, for the well-known to the beginning. 20s 20th century elem. h-ts - el-on and proton (and later neutron) the name "particle" was adopted.

The conclusion about the existence of A. was first made in 1931 by the English. physicist P. Dirac. He brought out the relative. quantum. ur-tion for e-on (Dirac equation), which turned out to be symmetrical with respect to the sign of the electric. charge: along with a negative charge. el-nom it described a positive charge. h-zu of the same mass - an antielectron. According to Dirac's theory, the collision of p-tsy and A. should lead to their annihilation - the disappearance of this pair, as a result of which two or more other p-ts are born, for example. photons.

In 1932, antielectrons were experimentally discovered by Amer. physicist K. Anderson. He photographed showers formed by cosmic rays in a cloud chamber placed in a magn. . Charge h-tsa moves in magn. field along an arc of a circle, and h-tsy with charges of different signs are deflected by the field in opposite sides. Along with the then well-known traces of fast e-news, Anderson found in the photographs exactly the same in appearance. mind traces positively charged. w-ts toy same masses. These people were called positrons. The discovery of the positron was a brilliant confirmation of Dirac's theory. Since that time, the search for other A.

In 1936 also in space. rays were found negative. and put. (m- and m+), which are h-tsey and A. in relation to each other. In 1947 it was found that muons cosm. rays arise as a result of the decay of somewhat more heavy h-ts- pi-mesons (p-, p+). In 1955, the first antiprotons were registered in experiments at the accelerator. Phys. the process that resulted in the formation of antiprotons was the proton - . Somewhat later, antineutrons were discovered. By 1981, A. of almost all known elements were experimentally discovered. h-ts.

The general principles of quantum field theory make it possible to draw a number of profound conclusions about the properties of the particle and the atom: the mass, spin, isotopic spin, the lifetime of the particle and its atom must be the same (in particular, stable particles correspond to stable BUT.); equal in magnitude, but opposite in sign must be not only electric. charges (and magn.) h-tsy and A., but also all other quantum. numbers that are attributed to people to describe the patterns of their effects: baryon charge, lepton charge, strangeness, "", etc. Ch-tsa, in which all the characteristics that distinguish it from A. are equal zero, called true neutral; h-ts and A. such h-ts are identical. These include, for example, p0- and h-mesons, J/y- and Y-particles.

Until 1956, it was believed that there was a complete between p-tsy and A. This means that if c.-l. process between p-tsami, then there must be exactly the same process between A. In 1956, it was discovered that such a symmetry exists only in strong and el.-magnet. vz-stvie. In a weak influence, a violation of the symmetry of particle-A was discovered. (see CHARGE COUPLE). From A., in principle, it can be built in exactly the same way as in-in from ch-ts. However, the possibility of annihilation when meeting human beings does not allow A. any longer. exist in in-ve. A. can “live” for a long time only if there is a complete absence of contact with people in the islands. Evidence of the presence of antimatter somewhere "close" to the Universe would be a powerful annihilation. , coming to Earth from the area of contact in-va and antimatter. But so far, astrophysics does not know the data that would speak of the existence in the Universe of regions filled with antimatter.

Physical encyclopedic Dictionary. - M.: Soviet Encyclopedia. . 1983 .

ANTIPARTICLES

Elementary particles having the same values of masses, spins, etc. physical. characteristics, as their "twins" - "particles", but differing from them in signs of certain interaction characteristics ( charges, e.g. electrical sign. charge).

The existence of A. was predicted by P. A. M. Dirac (P. A. M. Dirac). The quantum relativistic equation of motion of the electron obtained by him in 1928 (see. Dirac equation) necessarily contained solutions with neg. energies. Later it was shown that the disappearance of an electron with a negative energy should be interpreted as the emergence of a particle (of the same mass) with the positive. energy and positive. electric charge, i.e. A. with respect to the electron. This particle is positron - opened in 1932.

In subsequent experiments, it was found that not only , but also all other particles have their A. In 1936, in the cosmic. the rays were open muon and his A., and in 1947 - - and - mesons that make up a pair of particles A.; registered in 1955 in accelerator experiments antiproton, in 1956 - antineutron etc. To present. AAs have been observed for almost all known particles, and there is no doubt that AAs are present in all particles.

The existence and properties of A. are determined in accordance with the foundations. principle of quantum field theory - its invariance with respect to SRT transformations (cf. CPT theorem). From CPT-theorem it follows that , the spin and lifetime of the particle and its A. must be the same. In particular, stable (relative to decay) particles correspond to stable atoms (however, their existence in matter for any long time is impossible due to annihilation with matter particles). The states of particles and their A. are connected by the operation charge conjugation.

Therefore, the particle and A. have opposite electrical signs. charges (and magnetic moments) have the same isotopic spin, but differ in the sign of its third projection, have the same magnitude but opposite in sign strangeness, charm, beauty etc. Conversion combined inversion (CP) associates helical particles with states of A. of opposite helicity. Baryon and lepton numbers of the same magnitude, but opposite in sign, are assigned to particles and their amplitudes.

Due to the invariance with respect to charge conjugation ( With-invariance) of the strong and el.-mag. interactions connected by appropriate forces, composite objects from particles (atomic nuclei, atoms) and from atoms (nuclei and atoms antimatter) should have the same structure. For the same reason, the structure of hadrons and their acoustics coincide, moreover, within the framework of the model quarks the states of antibaryons are described in exactly the same way as the states of baryons with the replacement of constituent quarks by the corresponding ones antiquarks. The states of mesons and their A. are distinguished by the replacement of the components of the quark and antiquark by the corresponding and quark. For true neutral particles the states of the particle and the atom coincide. Such particles have certain charge parity(with-parity) and SR- parity. All known ones are bosons (for example, -mesons - with spin - with spin 1), however, in principle, truly neutral fermions can also exist (the so-called. Majorana particles).

Weak interaction is not invariant with respect to charge conjugation and, consequently, breaks the symmetry between particles and diamonds, which manifests itself in the difference of certain differentials. characteristics of their weak decays.

If k.-l. from the quantum numbers of an electrically neutral particle is not strictly conserved, then transitions (oscillations) between the states of the particle and its A are possible. In this case, states with a certain non-conserved quantum number are not proper. states of the energy-momentum operator, but are superpositions of truly neutral states with a definite. mass values. A similar phenomenon can be realized in systems, etc.

The very definition of what to call a "particle" in a particle-A. pair means. measure conditionally. However, when this choice"particles" of its A. is determined unambiguously. The conservation of the baryon number in the processes of weak interaction makes it possible to determine the "particle" in any baryon-antibaryon pair by the chain of baryon decays. The choice of an electron as a "particle" in an electron-positron pair fixes (due to the conservation of the lepton number in weak interaction processes) the definition of the state of a "particle" in a pair of electron neutrinos-antineutrinos. Transitions between leptons decomp. generations (of type ) have not been observed, so that the definition of a "particle" in each generation of leptons, generally speaking, can be made independently. Usually, by analogy with an electron, "particles" are called negatively charged. , which, with the conservation of the lepton number, determines the corresponding and antineutrinos. For bosons, the concept of "particle" can be fixed by the definition, for example, hypercharge.

The birth of A. occurs in the collisions of particles of matter accelerated to energies exceeding the threshold for the birth of a particle-A pair. (cm. birth of couples). In the lab A. conditions are born in the interactions of particles in accelerators; storage of the formed A. is carried out in storage rings under high vacuum. In nature. A. conditions are born during the interaction of primary cosmic. rays with matter, for example, the Earth's atmosphere, and should also be born in the vicinity pulsars and active galactic nuclei. Theoretical considers the formation of A. (positrons, antinucleons) during the accretion of matter on black holes. Within the framework of modern Cosmologists consider the birth of A. during the evaporation of primordial black holes of small mass.

At temp-pax exceeding the rest energy of particles of a given type (used = 1), the particle-A pair. are present in equilibrium with matter and e-mag. radiation. Such conditions can be realized for electron-positron in the hot cores of massive stars. According to the theory of the hot Universe, in the very early stages of the expansion of the Universe, particle-A pairs were in equilibrium with matter and radiation. all varieties. according to models great unification disruption effects C- and CP invariance in nonequilibrium processes with baryon number nonconservation could lead in the very early Universe to baryon asymmetry of the universe even under conditions of strict initial equality of the number of particles and A. This gives a physical. justification for the absence of observation. data on the existence of objects in the Universe from A.

Lit.: Dirac P. A. M., Principles of quantum mechanics, trans. from English, 2nd ed., M., 1979; Nishijima K., Fundamental particles, trans. from English, , 1965; Li Ts., Wu Ts., Weak interactions, trans. from English, M., 1968; Zeldovich Ya. V., Novikov I. D., Structure and evolution of the Universe, M., 1975. M. Yu. Khlopov.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1988 .

See what "ANTI-PARTICLES" is in other dictionaries:

Elementary particles that have the same mass, spin, lifetime and some other internal characteristics as their particle counterparts, but differ from particles in signs of electric charge and magnetic moment, baryon charge, lepton ... ... Big Encyclopedic Dictionary

ANTIPARTICLES, twins of elementary particles, in which masses and other physical characteristics have the same values as particles, and some characteristics, such as electric charge or magnetic moment, are opposite in sign. Almost all… … Modern Encyclopedia

antiparticles- ANTIPARTICLES, “twins” of elementary particles, whose masses and other physical characteristics have the same values as particles, and some characteristics, such as electric charge or magnetic moment, are opposite in sign. Almost… … Illustrated Encyclopedic Dictionary

ANTIPARTICLES- a set of elementary and many fundamental particles, the mass and (see) of which are exactly equal to the mass and spin of a given particle, and the electric charge, magnetic moment, and other similar characteristics are the same with the same characteristics of the particle, but ... ... Great Polytechnic Encyclopedia

An antiparticle is a twin particle of some other elementary particle, having the same mass and the same spin, but differing from it in signs of some interaction characteristics (charges, such as electric and color charges, baryon and ... ... Wikipedia

- twins of ordinary elementary particles, which differ from the latter by the sign of the electric charge and the signs of some other characteristics. Particles and antiparticles have the same masses, spins, and lifetimes. If the particle is also characterized by other internal quantum characteristics that have a sign, then the values of these characteristics for the antiparticle are the same, but the signs are opposite. If the particle is unstable (experiencing decay), then the antiparticle is also unstable, and their lifetimes coincide and the methods of decay coincide (up to replacement in the decay schemes of particles into antiparticles).
Ordinary matter consists of protons (p), neutrons (n) and electrons (e -). Antimatter consists of their antiparticles - antiprotons (), antineutrons () and antielectrons (positrons e +). The choice of which particles to consider as particles and which as antiparticles is conditional and determined by considerations of convenience. The antiparticle of an antiparticle is a particle. When a particle and an antiparticle collide, they disappear (annihilate), turning into gamma quanta.
In some cases (for example, a photon or π 0 -meson, etc.), the particle and the antiparticle completely coincide. This is due to the fact that the photon and π 0 -meson do not have an electric charge and other internal characteristics with a sign.

Characteristic	Particle	Antiparticle
Weight	M	M
Electric charge	+(-)Q	-(+)Q
Spin	J	J
Magnetic moment	+(-)μ	-(+)μ
baryon number	+B	-B
Lepton number	+L e , +L μ , +L τ	-L e , -L μ , -L τ
Weirdness	+(-)s	-(+)s
Charm	+(-)c	-(+)c
bottomness	+(-)b	-(+)b
topness	+(-)t	-(+)t
Isospin	I	I
Isospin projection	+(-)I 3	-(+)I 3
Parity	+(-)	-(+)
Lifetime	T	T
Decay scheme		charge conjugate

Antimatter consists of antiparticles - antiprotons, antineutrons and antielectrons - positrons e +. Particles and antiparticles are equal. The choice of which particles to consider as particles and which as antiparticles is conditional and determined by considerations of convenience. In the observable part of the Universe, matter consists of negatively charged electrons, positively charged protons and neutrons.
When an electron and a positron collide, they disappear (annihilate), turning into gamma quanta. During the annihilation of strongly interacting particles, for example, a proton and an antiproton, several mesons π + , π - , π 0 , K + , K - , K 0 are formed.

In accordance with the Dirac equation, the meeting of an electron with a positron has fatal consequences for them - both particles disappear. Such an amazing prediction and its experimental confirmation made a strong impression on both physicists and non-physicists - after all, this was the first example of a complete transformation of matter into radiation. The newly discovered effect was called annihilation, which in Latin means complete annihilation.

So far, no one has been able to detect cosmic antihelium and gamma radiation with a specific spectrum due to annihilation at the boundaries of matter and antimatter clusters.

In fact, the assertion that the interaction of particles and antiparticles invariably entails the creation of photons is false even with respect to electrons and positrons. A free electron-positron pair annihilates with the formation of electromagnetic quanta only if its energy is not too high. Very fast electrons and positrons are capable of generating positive and negative pi-mesons (they are also pions), plus- and minus-muons, protons and antiprotons, and even even heavier particles - only energy would be enough. Slow protons and antiprotons during annihilation give rise to charged and neutral pions (and fast ones to other particles), which decay into gamma quanta, muons and neutrinos. In principle, the collision of a particle and its anticopy can result in any of the combinations of particles that are not forbidden by the principles of symmetry and conservation laws.

It may seem that annihilation is no different from other interparticle interactions, but it has one fundamental feature. In order for stable particles, such as protons or electrons, to give rise to a shower of exotic inhabitants of the microcosm when they meet, they need to be properly dispersed. Slow protons will simply change their speed when they meet - this is the end of the matter. But the proton and antiproton, approaching, either undergo elastic scattering and disperse, or annihilate and produce secondary particles.

All of the above refers to the annihilation of free particles. If at least one of them is part of a quantum system, the situation remains the same in principle, but the alternatives change. For example, the annihilation of a free electron and a free positron can never give rise to just one quantum - the law of conservation of momentum does not allow it. This is easiest to see if you work in the system of the center of inertia of the colliding pair - then the initial momentum will be zero and therefore cannot coincide with the momentum of a single photon, no matter where it flies. If a positron meets an electron that is, say, part of a hydrogen atom, one-photon annihilation is also possible - in this case, part of the momentum is transferred to the atomic nucleus.

The main ways to search for antimatter are the registration of radiation with an energy characteristic of annihilation, or the direct registration of antiparticles by mass and charge. Since antiprotons and antihelium nuclei cannot fly through the atmosphere, they can only be detected with the help of instruments raised into the high layers of the atmosphere on balloons, or orbital instruments, such as the AMS-01 magnetic alpha spectrometer delivered to the Mir station in 1998 , or its much-improved cousin AMS-02 (pictured), which will begin operations on the ISS in 2010.

How about antigrav?

The English physicist Arthur Schuster believed that antimatter gravitationally repels ordinary matter, but modern science considers this unlikely. From the most general principles of symmetry of the laws of the microworld, it follows that antiparticles should be attracted to each other by gravity, like particles without the prefix "anti". The question of what is the gravitational interaction of particles and antiparticles has not yet been fully resolved, but the answer to it is almost obvious.

Let's start with Einstein's general theory relativity. It is based on the principle of strict equality of gravitational and inertial masses, and for ordinary matter this statement has been experimentally confirmed by many very precise measurements. Since the inertial mass of a particle is exactly equal to the mass of its antiparticle, it seems very likely that their gravitational masses are also equal. However, this is still an assumption, albeit a very plausible one, and it cannot be proved by means of general relativity.

Another argument against gravitational repulsion between matter and antimatter follows from quantum mechanics. Recall that hadrons (particles that take part in strong interactions) are made up of quarks glued together by gluon bonds. Each baryon consists of three quarks, while mesons consist of paired combinations of quarks and antiquarks, and not always the same (a meson, which includes a quark and its own antiquark, is a truly neutral particle in the sense that it is completely identical to its antimeson). However, these quark structures cannot be considered absolutely stable. A proton, for example, is composed of two u-quarks, each of which carries an elementary electric charge of +2/3, and one d-quark with a charge of -1/3 (therefore, the proton's charge is +1). However, these quarks, as a result of interaction with gluons, can change their nature for a very short time - in particular, they can turn into antiquarks. If particles and antiparticles gravitationally repel each other, the weight of the proton (and also, of course, the neutron) should oscillate slightly. However, so far no such effect has been found in a single laboratory.

Antimatter and the Milky Way

In the 1970s, astronomers using gamma-ray telescopes mounted on high-altitude balloons detected gamma rays with an energy of 511 keV coming from the very center of our Galaxy, the Milky Way. It is this energy that is characteristic of the annihilation of free electrons and positrons, which made it possible to assume the presence of an antimatter cloud with a size of about 10,000 light years.

There is no doubt that someday His Majesty Experiment will answer this question. It doesn't take much - to accumulate more antimatter and see how it behaves in the Earth's gravitational field. However, technically, these measurements are incredibly complex, and it is difficult to predict when they will be able to be implemented.

So what's the difference?

After the discovery of the positron for a quarter of a century, almost all physicists were sure that nature does not distinguish between particles and antiparticles. More specifically, it was believed that any physical process involving particles corresponds to exactly the same process involving antiparticles, and both of them are carried out with the same probability. Available experimental data testified that this principle is observed for all four fundamental interactions - strong, electromagnetic, weak and gravitational.

And then all at once everything changed dramatically. In 1956, the American physicists Li Zong-dao and Yang Jenning published a Nobel Prize-winning paper in which they discussed the difficulties associated with the fact that two seemingly identical particles, thetameson and thaumeson, decay into different number peonies. The authors emphasized that this problem can be solved by assuming that such decays are associated with processes whose character changes during the transition from right to cool, in other words, during mirror reflection (a little later, physicists realized that in general view we need to talk about reflections in each of the three coordinate planes - or, what is the same, about changing the signs of all spatial coordinates, spatial inversion). This means that the mirrored process may be banned or occur with a different probability than before the mirroring. A year later, American experimenters (belonging to two independent groups and working by different methods) confirmed that such processes do exist.

This was just the beginning. At the same time, theoretical physicists from the USSR and the USA realized that the violation of mirror symmetry makes possible the violation of symmetry with respect to the replacement of particles by antiparticles, which was also repeatedly proved in experiments. It is worth noting that not long before Lee and Yang, but still in the same 1956, the possibility of breaking mirror symmetry was discussed by the experimental physicist Martin Block and the great theorist Richard Feynman, but they never published these considerations.

Physicists traditionally refer to mirror reflection with the Latin letter P, and the replacement of particles with their antiparticles with the letter C. Both symmetries are violated only in processes involving the weak interaction, the very one that is responsible for the beta decay of atomic nuclei. It follows that it is due to weak interactions that there are differences in the behavior of particles and antiparticles.

During one of the last shuttle missions (STS-134) in 2010, a new scientific instrument, the Alpha Magnetic Spectrometer (AMS-02, Alpha Magnetic Spectrometer), will be delivered to MSC. Its AMS-01 prototype was delivered aboard the Mir space station in 1998 and proved the viability of the concept. The main goal of the scientific program will be to study and measure with high precision the composition of cosmic rays, as well as to search for exotic forms of matter - dark matter, strange matter (particles that contain strange (s) quarks), as well as antimatter - in particular, antihelium nuclei .

A strange violation of mirror symmetry brought to life attempts to compensate for it in some way. Already in 1956, Lee and Yang, and independently Lev Landau, suggested that nature does not distinguish between systems that are obtained from each other by applying the C and P transformations together (the so-called CP symmetry). From the point of view of theory, this hypothesis looked very convincing and, moreover, fit well with the experimental data. However, just eight years later, employees of the Brookhaven National Laboratory discovered that one of the uncharged K-mesons (or, as they are also called, kaons) can decay into a pion pair. With strict adherence to CP-symmetry, such a transformation is impossible - and therefore, this symmetry is not universal! True, the share of supposedly forbidden decays did not exceed 0.2%, but they still took place! The discovery earned Brookhaven team leaders James Cronin and Val Fitch the Nobel Prize in Physics.

Symmetry and antimatter

CP violations are directly related to the difference between matter and antimatter. In the late 1990s, a very beautiful experiment was done at CERN with neutral K0 kaons, each of which consists of a d quark and a more massive strange antiquark. The laws of nature allow the antiquark to lose some of its energy and turn into an anti-d. The released energy can be used to decay the kaon, but it is possible that the neighboring d-quark will absorb it and turn into a strange quark. As a result of this, a particle will appear, consisting of an anti-d-quark and a strange quark, that is, a neutral antikaon. Formally, this transformation can be described as the result of applying the CP transformation to the kaon!

Thus, if CP symmetry is observed absolutely strictly, then neutral kaons K0 transform into their antiparticles with exactly the same probability as they undergo reverse transformations. Any violation of CP symmetry will entail a change in one of these probabilities. If we prepare a beam of an equal number of neutral kaons and antikaons and follow the dynamics of the concentration of both particles, we can find out whether their quantum oscillations respect CP symmetry.

This is exactly what CERN physicists have done. They found that neutral antikaons become kaons a little faster than they turn into antikaons. In other words, a process was discovered during which antimatter turns into matter faster than matter into antimatter! In a mixture with initially equal proportions of matter and antimatter, over time, even a small, but still measurable excess of matter is formed. The same effect was revealed in experiments with other heavy neutral particles, D0 mesons and B0 mesons.

Thus, by the end of the 20th century, experimenters had convincingly proved that weak interactions affect particles and antiparticles in different ways. Although these differences are very small in themselves and only come to light in the course of certain transformations of very exotic particles, they are all quite real. This means the presence of physical asymmetry between matter and antimatter.

To complete the picture, one more circumstance should be noted. In the 1950s, the most important proposition of relativistic quantum mechanics, the CPT theorem, was proved. It says that particles and antiparticles are strictly symmetric with respect to the CP transformation, followed by time reversal (strictly speaking, this theorem is true only without taking into account gravity, otherwise the question remains open). Therefore, if CP symmetry is not observed in some processes, their speed in the "forward" and "reverse" directions (what to consider as both, of course, is a matter of agreement) should not be the same. This is precisely what the experiments at CERN with neutral kaons proved.

The AMS-02 mission will last about seven years. The seven-ton module docked to the ISS is expected to detect more than 1 billion helium nuclei and several antihelium nuclei. The predecessor of this detector, AMS-01, registered about 1 million helium nuclei, but did not detect antihelium.

Where are the anti-worlds?

In 1933, Paul Dirac was sure that in our Universe there are entire islands of antimatter, which he mentioned in his Nobel lecture. However, modern scientists believe that there are no such islands either in our Galaxy or beyond.

Of course, antimatter as such exists. Antiparticles are generated by many high-energy processes, such as the thermonuclear burning of stellar fuel and supernova explosions. They arise in magnetized plasma clouds surrounding neutron stars and black holes, during collisions of fast cosmic particles in interstellar space, when the earth's atmosphere is bombarded by cosmic rays, and, finally, in accelerator experiments. In addition, the decay of some radionuclides is accompanied by the formation of antiparticles, namely positrons. But all this is only antiparticles, and by no means antimatter. So far, no one has been able to detect even cosmic antihelium, let alone heavier elements. The search for gamma radiation with a specific spectrum, caused by annihilation at the boundaries of cosmic clusters of matter and antimatter, was also unsuccessful.

Reports periodically appear in the scientific literature about the discovery of non-standard primary sources of cosmic antiparticles of unknown origin. In April 2009, data were published on a mysterious excess of extremely fast positrons detected by the PAMELA detector complex. This equipment is located on board Russian satellite"Resurs-DK1", June 15, 2006 sent into low Earth orbit from the Baikonur Cosmodrome. Some experts interpreted this result as possible evidence of the annihilation of hypothetical dark matter particles, but a less exotic explanation soon emerged. This hypothesis was commented for "PM" by a well-known specialist in cosmic rays Veniamin Berezinsky from the Gran Sasso National Laboratory, which is part of the Italian National Institute of Nuclear Physics: "The standard model for the production of galactic cosmic rays rests on three positions. Supernova remnants are considered the first and main source of charged particles. The second idea is that particles are accelerated to ultrarelativistic velocities at the fronts of post-explosion shock waves, and the role of their own energy is very large in this acceleration. magnetic field. The third proposition is that cosmic rays propagate by diffusion. My former student and now professor at the National Institute of Astrophysics Pasquale Blasi showed that the excess of positrons detected by the PAMELA complex is quite consistent with this model. Protons dispersed in shock waves collide with particles of cosmic gas and it is in this zone of their acceleration that they turn into positive pions, which decay with the formation of positrons and neutrinos. According to Blazy's calculations, this process could very well produce exactly the same concentration of positrons that PAMELA found. Such a mechanism for generating positrons looks absolutely natural, but for some reason it has never occurred to anyone until now. Blasi also showed that the same processes should also generate excess antiprotons. However, the cross section of their production is much smaller than the corresponding value for positrons, because of which they can be detected only at higher energies. I think that over time it will become possible.”

World or anti-world?

Let's imagine that we are flying on an interstellar ship that is approaching a planet with intelligent life. How do we know what our brothers in mind are made of - matter or antimatter? You can send a reconnaissance probe, but if it explodes in the atmosphere, we may be considered space aggressors, as happens in Krzysztof Borun's science fiction novel Antiworld. This can be avoided by using the same neutral kaons and antikaons. As already mentioned, they are able not only to turn into each other, but also to disintegrate, and in different ways. In particular, neutrinos accompanied by either positive pions and electrons or negative pions and positrons can be produced in such decays. Due to the asymmetry between matter and antimatter, the rates of such reactions are somewhat different. This circumstance can be used as a "litmus test". To test an alien planet for antimateriality, it is convenient to take not pure kaons and antikaons, but their mixed states, which are usually denoted as Ks and Kl (s is short, and l is long). The fact is that in state L, the life span of a particle is 570 times longer than in state S (5.12x10^-8 sec versus 8.95x10^-11 sec). In the long-lived version of kaons, the symmetry of matter and antimatter is much stronger - for every 10 thousand decays of the desired type, approximately 5015 produce positrons, and 4985 electrons. By the way, we note that the historical experiment of Cronin and Finch was also made on Kl-mesons. And now let's start a conversation with brothers in mind. Kaons have a characteristic mass slightly more than half that of a proton. Let's explain to our negotiating partners that we need an unstable neutral particle, the mass of which is slightly larger than the mass of the nucleus of the simplest of atoms. Extraterrestrial physicists will understand what it is about, make Kl-mesons and determine the characteristics of their decays that are of interest to us. When they succeed in this, we will ask whether the sign of the electric charge of the lightest of the charged particles, generated in these decays a little more often than a similar particle of the opposite sign, coincides with the sign of the particles that make up the atoms of their world. In the case of a positive answer, it will become clear to us that positrons are part of their atoms and, therefore, the alien consists of antimatter. And if the answer is negative - you can prepare for landing!

In general, so far everything speaks for the fact that there are no antistars, no antiplanets, or even the smallest antimeteors in space. On the other hand, conventional Big Bang models state that shortly after birth, our universe contained the same number of particles and antiparticles. So why did the former survive and the latter disappear?.. Read the answer to this question in one of the following articles.

The article "The War of Particles and Antiparticles: Who Remains on the Battlefield" was published in the journal Popular Mechanics (

There was no reason to assume that the existence of a positron, or, as it is better to call it now, an antielectron, is a feature of small particles. Despite a number of specific features, the theory of interaction between nucleons develops along the same lines as the theory of interaction of electrons. In most theoretical papers, it is assumed that nucleons should be described by equations quite similar to the Dirac equations for electrons. If so, then for nucleons one should expect the existence of antiparticles located in the same

relation to the proton and neutron, in which the positron and electron are located. Experience has shown that this is exactly the case for the proton. A little later, the antineutron was also discovered, which differs from the neutron in the direction of the magnetic moment (for a neutron, the magnetic moment and the rotational momentum vector are antiparallel, and for an antineutron, they are parallel).

Rice. 246. (see scan)

The discovery of the antiproton shows the validity of the general idea - the inseparable connection of the field with particles. Just like a pair of positrons -

an electron, a proton-antiproton pair can arise by transferring a nucleon from a state of negative energy to a state with positive energy. For this purpose, energy is required no less than This is a huge energy, 1840 times greater than the energy needed to create an electron-positron pair. Billions of electron volt accelerators were needed to make the discovery of the antiproton possible.

When a proton meets an antiproton, they will annihilate. Since nucleons transfer energy through the meson field, during annihilation their mass and energy will be given to the quanta of this field - mesons.

There is no doubt that this process will be studied in detail in the coming years.

On fig. 246 shows a photograph of the annihilation of a proton and an antiproton. The process was observed in a bubble chamber filled with liquid propane. The process diagram is shown at the top left.

Considerations about the need for the existence of antiparticles apply to neutrinos as well. The "mirror" image is called an antineutrino. The difference between the particles that make up the doublet is the same as that of the neutron and antineutron.

In the form of a doublet, there are also muons, as well as other elementary particles, which we did not talk about.

Muons are a triplet: the muon occurs in the form of varieties with plus and minus charges, as well as with a charge, zero. Unlike the neutron and the neutrino, a spinless neutral muon cannot have an antiparticle (one can also say: it coincides with its antiparticle). Another particle that does not have a "reflection" is a photon.

GOSKOMVUZ RF

Department of General Physics

Topic: ”Antiparticles”

FACULTY: AWTF

GROUP: A-513

STUDENT: Efimenko D.V.

Lecturer: Usoltseva N.Ya.

Novosibirsk

Antimatter is matter built from antiparticles. The existence of antiparticles was first predicted in 1930 by the English physicist P. Dirac. From the Dirac equation for a relativistic electron, the second solution followed for its twin, which has the same mass and positive electric charge. At the same time, only one positively charged particle was known - the proton, which differed sharply in its properties from the electron. Theorists began to come up with clever explanations for these differences, but it soon became clear that the proton had nothing to do with the particle predicted by Dirac. In 1932, positively charged positrons were discovered in cosmic rays by the American physicist K. Anderson. This discovery was a brilliant confirmation of Dirac's theory.

In 1955, at a new accelerator in Berkeley, E. Segre, O. Chamberlain and others discovered antiprotons produced in the collision of protons with the nuclei of a copper target. Prior to this, a proton with a negative charge had long been unsuccessfully searched for in cosmic rays. The antineutron was also discovered in 1956. Now many particles are already known, and almost all of them correspond to antiparticles.

Particles and antiparticles have the same mass, lifetime, spin, but differ in the signs of all charges: electric, baryon, lepton, etc. This follows from the general principles of quantum field theory and is confirmed by reliable experimental data.

From the modern point of view, elementary particles are divided into two groups. The first of them are particles with half-integer spin: charged leptons e - , m - , t - , their corresponding neutrinos and quarks u, d, c, b, t. All of these particles also have antiparticles. The other group is the quanta of fields with integer spin, carrying interactions: photon, intermediate bosons of weak interactions, gluons of strong interactions. Some of them are truly neutral (g, Z 0), that is, all their quantum numbers are equal to zero and they are identical to their antiparticles; others (W + , W -) also form particle-antiparticle pairs. It is easy to see now that all baryons consisting of three quarks must have antiparticles, for example: the neutron has composition (

), antineutron - ( ). Mesons consist of a quark and an antiquark and, generally speaking, also have antiparticles, for example: p - - meson consists of quarks ( ), and p + meson consists of quarks ( ). At the same time, there are mesons that are symmetrical with respect to the replacement of quarks by antiquarks (for example, p 0 ,r,h- mesons, which include pairs of quarks , and ); also the mesons will be truly neutral.

A characteristic feature of the behavior of particles and antiparticles is their annihilation upon collision. Even Dirac predicted the process of annihilation of electrons and positrons into photons: e - + e + ®g + g. Annihilation processes proceed, of course, with the conservation of energy, momentum, electric charge, etc. In this case, not only photons, but also other particles can be born; It is obvious that due to the laws of conservation of various charges, the corresponding antiparticles are simultaneously born, as, for example, in the reaction of annihilation of an electron and a positron into a pair of muons: e - + e + ®m - + m + . In such reactions, "enchanted" and "charming" particles were discovered. In a similar process, e - + e + ®t - + t + discovered a heavy t - lepton. AT last years the process of annihilation is increasingly used as one of the most advanced methods for studying the microworld.

The operation of replacing particles with antiparticles is called charge conjugation. Since truly neutral particles are identical to their antiparticles, they transform into themselves during the charge conjugation operation.

In strong and electromagnetic interactions, there is a complete symmetry between particles and antiparticles: if some process with particles is possible, then a similar process with the corresponding antiparticles is possible and has the same characteristics. Just as protons and neutrons bind into nuclei due to the strong interaction, antinuclei will be formed from the corresponding antiparticles.

In 1965, an antideuteron was obtained at an accelerator in the USA. In 1969, in Protvino, at the accelerator of the Institute of High Energy Physics, Soviet physicists discovered antihelium-3 nuclei, consisting of two antiprotons and an antineutron. Then the nuclei of antitritium were discovered - heavy antihydrogen, consisting of one antiproton and two antineutrons. In principle, one can imagine both anti-atoms and even large accumulations of antimatter. Evidence of the presence of antimatter in the Universe was a powerful annihilation radiation coming from the areas of contact between matter and antimatter.

After all, the annihilation of only 1 gram of matter and antimatter leads to the release of 10 14 J of energy, which is equivalent to the explosion of an average atomic bomb of 10 kilotons. However, astrophysics does not yet have such data, and even in cosmic rays, antiprotons are quite rare. Now there is practically no doubt that the Universe mainly consists of ordinary matter.

But it was not always so. On the early stage During the development of the Universe at very high temperatures around 10 13 K, the number of particles and antiparticles almost coincided: for a large number of antiprotons (approximately for every several billion), there were the same number of protons and one more “extra” proton. Later, when the Universe cooled down, all particles and antiparticles annihilated, eventually giving rise to photons, and everything that now surrounds us arose from an insignificant excess of particles in the past. Annihilation photons, gradually cooling down, have survived to this day in the form of relic radiation. The ratio of the current density of protons to the density of relic photons (10 -9) gave information about the magnitude of the excess of particles over antiparticles in the past. If this excess were not there, then there would be a complete mutual annihilation of particles and antiparticles and, as a result, a rather dull Universe filled with cold photon gas would arise.

Where did this excess come from? One of the hypotheses suggests that in the initial state the number of particles and antiparticles coincided, but then, due to the peculiarities in the dynamics of their interaction, an asymmetry arose.

Annihilation is the only process in which both initial particles disappear and their entire mass is completely converted, for example, into photon energy. No other reaction used in the energy sector has this property. Both in the fission of uranium and in the processes of thermonuclear fusion, only a small part (on the order of tenths of a percent) of the rest mass of the particles participating in the reaction is converted into energy. Therefore, the annihilation of antimatter with matter gives a thousand times more energy than the fission of the same amount of uranium. If we had a small planet of antimatter at our disposal, then all the problems with the energy crisis would immediately disappear. Suppose we would learn to convert all the energy of annihilation into electrical energy. Then, in order to provide the planet with an annual supply of electricity, it is necessary to split off from the planet and subject to annihilation only a 1000-kilogram piece of antimatter. Compare those 1,000 kilograms to the hundreds of millions of tons of coal and oil that we mine every year to solve the same problem!

How much energy is released per 1 gram of fuel

1. Annihilation of matter and antimatter 10 14 joules

2. Fission of uranium 10 11 joules

3. Burning coal 2.9- 10 4 joules

Antimatter would also be an ideal fuel because it does not pollute environment. After annihilation, only high-energy photons and neutrinos ultimately remain.

Our Earth is regularly bombarded by a stream of cosmic rays - high-energy particles that are generated during various processes occurring in our Galaxy. Most of these particles are protons and helium nuclei.

But recently, in 1979, antiprotons were also found in cosmic rays. Two groups reported this at once: Soviet physicists from the Leningrad Institute of Physics and Technology named after A. I. Ioffe and American scientists from the L. Johnson Space Flight Center. The positron was discovered in cosmic rays in 1932. Such a long time interval between the discovery of a positron and an antiproton in cosmic rays is explained by the fact that the antiproton interacts much more strongly with matter than the positron. antiprotons from space do not have time to reach the Earth's surface, they annihilate already in the uppermost layers of the atmosphere. That is why the search for antiprotons in cosmic rays is a complex technical problem. It is necessary to raise the detector as high as possible, to the edge of the atmosphere. All experiments on the search for antiparticles in cosmic rays were carried out on balloons. For example, in the experiments of R. Golden, a balloon lifted approximately 2 tons of equipment to a height of 36 kilometers.