This interaction is the weakest of the fundamental interactions experimentally observed in the decays of elementary particles, where quantum effects are fundamentally significant. Recall that quantum manifestations gravitational interaction have never been observed. Weak interactions are highlighted using next rule: if an elementary particle called a neutrino (or antineutrino) is involved in the interaction process, then this interaction is weak.
The weak interaction is much more intense than the gravitational interaction.
The weak interaction, unlike the gravitational interaction, is short-range. This means that the weak force between particles only comes into play if the particles are close enough to each other. If the distance between particles exceeds a certain value called the characteristic radius of interaction, the weak interaction does not manifest itself. It has been experimentally established that the characteristic radius of weak interaction is about 10-15 cm, that is, weak interaction is concentrated at distances smaller sizes atomic nucleus.
Why can we talk about weak interaction as an independent type of fundamental interaction? The answer is simple. It has been established that there are processes of transformation of elementary particles that are not reduced to gravitational, electromagnetic and strong interactions. Good example, showing that there are three qualitatively different interactions in nuclear phenomena, is associated with radioactivity. Experiments indicate the presence of three various types radioactivity: a-, b and g-radioactive decays. In this case, a-decay is due to strong interaction, g-decay is due to electromagnetic interaction. The remaining b-decay cannot be explained by the electromagnetic and strong interactions, and we are forced to accept that there is another fundamental interaction, called the weak. In the general case, the need to introduce weak interaction is due to the fact that processes occur in nature in which electromagnetic and strong decays are prohibited by conservation laws.
Although the weak interaction is significantly concentrated within the nucleus, it has certain macroscopic manifestations. As we have already noted, it is associated with the process of b-radioactivity. In addition, the weak interaction plays an important role in the so-called thermonuclear reactions responsible for the mechanism of energy release in stars.
The most amazing property weak interaction is the existence of processes in which mirror asymmetry is manifested. At first glance, it seems obvious that the difference between the concepts left and right is arbitrary. Indeed, the processes of gravitational, electromagnetic and strong interaction are invariant with respect to spatial inversion, which carries out mirror reflection. It is said that in such processes the spatial parity P is conserved. However, it has been experimentally established that weak processes can proceed with non-conservation of spatial parity and, therefore, seem to sense the difference between left and right. Currently, there is solid experimental evidence that parity nonconservation in weak interactions is universal in nature; it manifests itself not only in the decays of elementary particles, but also in nuclear and even atomic phenomena. It should be recognized that mirror asymmetry is a property of Nature at the most fundamental level.
All charged bodies, all charged elementary particles participate in electromagnetic interaction. In this sense, it is quite universal. The classical theory of electromagnetic interaction is Maxwellian electrodynamics. The electron charge e is taken as the coupling constant.
If we consider two things at rest point charge q1 and q2, then their electromagnetic interaction will be reduced to a known electrostatic force. This means that the interaction is long-range and decays slowly as the distance between the charges increases. A charged particle emits a photon, causing its state of motion to change. Another particle absorbs this photon and also changes its state of motion. As a result, the particles seem to sense the presence of each other. It is well known that electric charge is a dimensional quantity. It is convenient to introduce the dimensionless coupling constant of electromagnetic interaction. To do this, you need to use the fundamental constants and c. As a result, we arrive at the following dimensionless coupling constant, called atomic physics constant fine structure
It is easy to see that this constant significantly exceeds the constants of gravitational and weak interactions.
From a modern point of view, electromagnetic and weak interactions represent different sides unified electroweak interaction. A unified theory of electroweak interaction has been created - the Weinberg-Salam-Glashow theory, which explains all aspects of electromagnetic and weak interactions from a unified position. Is it possible to understand at a qualitative level how the division of the combined interaction into separate, seemingly independent interactions occurs?
As long as the characteristic energies are sufficiently small, the electromagnetic and weak interactions are separated and do not affect each other. As the energy increases, their mutual influence begins, and at sufficiently high energies these interactions merge into a single electroweak interaction. The characteristic unification energy is estimated in order of magnitude to be 102 GeV (GeV is short for gigaelectron-volt, 1 GeV = 109 eV, 1 eV = 1.6 10-12 erg = 1.6 1019 J). For comparison, we note that the characteristic energy of an electron in the ground state of a hydrogen atom is about 10-8 GeV, the characteristic binding energy of an atomic nucleus is about 10-2 GeV, and the characteristic binding energy of a solid is about 10-10 GeV. Thus, the characteristic energy of the combination of electromagnetic and weak interactions is enormous compared to the characteristic energies in atomic and nuclear physics. For this reason, electromagnetic and weak interactions do not manifest their single essence in ordinary physical phenomena.
The strong interaction is responsible for the stability of atomic nuclei. Since the atomic nuclei of most chemical elements are stable, it is clear that the interaction that keeps them from decay must be quite strong. It is well known that nuclei consist of protons and neutrons. To prevent positively charged protons from flying apart different sides, it is necessary to have attractive forces between them that exceed the forces of electrostatic repulsion. It is the strong interaction that is responsible for these attractive forces.
A characteristic feature of the strong interaction is its charge independence. The nuclear forces of attraction between protons, between neutrons, and between a proton and a neutron are essentially the same. It follows that from the point of view of strong interactions, a proton and a neutron are indistinguishable and the single term nucleon, that is, a nuclear particle, is used for them.
So, we have reviewed the basic information regarding the four fundamental interactions of Nature. The microscopic and macroscopic manifestations of these interactions and the picture of physical phenomena in which they play an important role are briefly described.
MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA
Federal state budget educational institution
higher professional education
"St. Petersburg State Electrotechnical University "LETI" named after V. I. Ulyanov (Lenin)"
(SPbGETU)
Faculty of Economics and Management
Department of Physics
In the discipline "Concepts" modern natural science"
on the topic "Weak interaction"
Checked:
Altmark Alexander Moiseevich
Performed:
student gr. 3603
Kolisetskaya Maria Vladimirovna
Saint Petersburg
1. The weak interaction is one of the four fundamental interactions
History of the study
Role in nature
The weak force is one of the four fundamental forces
The weak force, or weak nuclear force, is one of the four fundamental forces
The weak interaction is short-range - it manifests itself at distances significantly smaller than the size of the atomic nucleus
Vector bosons are carriers of the weak interaction
For the first time, weak interactions were observed during the decay of atomic nuclei. And, as it turned out, these decays are associated with the transformation of a proton into a neutron in the nucleus and vice versa:
R? n + e+ + ?e, n ? p + e- + e,
where n is a neutron, p is a proton, e- is an electron, ??e is an electron antineutrino.
Elementary particles are usually divided into three groups:
) photons; this group consists of only one particle - a photon - a quantum electromagnetic radiation;
) leptons (from the Greek “leptos” - light), participating only in electromagnetic and weak interactions. Leptons include the electron and muon neutrino, the electron, the muon and the heavy lepton discovered in 1975 - the t-lepton, or taon, with a mass of approximately 3487me, as well as their corresponding antiparticles. The name leptons is due to the fact that the masses of the first known leptons were smaller than the masses of all other particles. Leptons also include the secret neutrino, whose existence in Lately also installed;
) hadrons (from the Greek “adros” - large, strong). Hadrons have strong interactions along with electromagnetic and weak ones. Of the particles discussed above, these include the proton, neutron, pions and kaons.
Properties of the weak interaction
The weak interaction has distinctive properties:
All fundamental fermions take part in weak interaction
Operation P changes the sign of any polar vector
The operation of spatial inversion transforms the system into a mirror symmetric one. Mirror symmetry is observed in processes under the influence of strong and electromagnetic interactions. Mirror symmetry in these processes means that in mirror-symmetric states transitions are realized with the same probability.
G. ? Yang Zhenning, Li Zongdao received Nobel Prize in physics. For his in-depth studies of the so-called parity laws, which led to important discoveries in the field of elementary particles.
In addition to spatial parity, the weak interaction also does not preserve combined space-charge parity, that is, the only known interaction violates the principle of CP invariance
Charge symmetry means that if there is any process involving particles, then when they are replaced by antiparticles (charge conjugation), the process also exists and occurs with the same probability. Charge symmetry is absent in processes involving neutrinos and antineutrinos. In nature, only left-handed neutrinos and right-handed antineutrinos exist. If each of these particles (for definiteness, we will consider the electron neutrino? e and antineutrino e) is subjected to the operation of charge conjugation, then they will turn into non-existent objects with lepton numbers and helicities.
Thus, in weak interactions, P- and C-invariance are violated simultaneously. However, what if two consecutive operations are performed on a neutrino (antineutrino)? P- and C-transformations (the order of operations is not important), then we again obtain neutrinos that exist in nature. Sequence of operations and (or in reverse order) is called the CP transformation. The result of the CP transformation (combined inversion) of ?e and e is as follows:
Thus, for neutrinos and antineutrinos, the operation that transforms a particle into an antiparticle is not a charge conjugation operation, but a CP transformation.
History of the study
The study of weak interactions continued for a long period.
In 1896, Becquerel discovered that uranium salts emit penetrating radiation (γ decay of thorium). This was the beginning of the study of weak interactions.
In 1930, Pauli put forward the hypothesis that during ? decay, along with electrons (e), light neutral particles are emitted? neutrino (?). In the same year, Fermi proposed a quantum field theory of β-decay. The decay of a neutron (n) is a consequence of the interaction of two currents: the hadronic current converts a neutron into a proton (p), the leptonic current produces an electron + neutrino pair. In 1956, Reines first observed the reaction of er? ne+ in experiments near nuclear reactor.
Lee and Yang explained the paradox in the decays of K+ mesons (? ~ ? mystery)? decay into 2 and 3 pions. It is associated with non-conservation of spatial parity. Mirror asymmetry has been discovered in the β-decay of nuclei, the decays of muons, pions, K-mesons and hyperons.
In 1957, Gell-Mann, Feynman, Marshak, and Sudarshan proposed a universal theory of weak interaction based on the quark structure of hadrons. This theory, called V-A theories, led to the description of the weak interaction using Feynman diagrams. At the same time, fundamentally new phenomena were discovered: violation of CP invariance and neutral currents.
In the 1960s by Sheldon Lee Glashow
In 1991-2001, a study of the decays of Z0 bosons was carried out at the LEP2 accelerator (CERN), which showed that in nature there are only three generations of leptons: ?e, ?? And??.
Role in nature
nuclear interaction is weak
The most common process caused by weak interaction is the b-decay of radioactive atomic nuclei. Radioactivity phenomenon<#"justify">Bibliography
1. Novozhilov Yu.V. Introduction to the theory of elementary particles. M.: Nauka, 1972
Okun B. Weak interaction of elementary particles. M.: Fizmatgiz, 1963
Weak interaction
Strong interaction
Strong interaction is short-acting. Its range of action is about 10-13 cm.
Particles participating in strong interactions are called hadrons. In an ordinary stable substance, not too much high temperature strong interaction does not cause any processes. Its role is to create a strong bond between nucleons (protons and neutrons) in nuclei. The binding energy averages about 8 MeV per nucleon. Moreover, in collisions of nuclei or nucleons with sufficient high energy(on the order of hundreds of MeV), strong interaction leads to numerous nuclear reactions: fission of nuclei, transformation of some nuclei into others, etc.
Starting from energies of colliding nucleons of the order of several hundred MeV, strong interaction leads to the production of P-mesons. At even higher energies, K-mesons and hyperons, and many meson and baryon resonances are born (resonances are short-lived excited states of hadrons).
At the same time, it turned out that not all particles experience strong interaction. Thus, protons and neutrons experience it, but electrons, neutrinos and photons are not subject to it. Usually only heavy particles participate in strong interactions.
The theoretical explanation of the nature of the strong interaction has been difficult to develop. A breakthrough emerged only 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 strong interaction quanta are eight gluons. Gluons get their name from English word glue (glue), because they are responsible for the confinement of quarks. The rest masses of gluons are zero. At the same time, gluons have a colored charge, due to which they are capable of interacting with each other, as they say, of self-interaction, which leads to difficulties in describing the strong interaction mathematically due to its nonlinearity.
Its range of action is less than 10-15 cm. The weak interaction is several orders of magnitude weaker not only than the strong one, but also the electromagnetic one. Moreover, it is much stronger than gravitational force in the microcosm.
The first discovered and most common process caused by the weak interaction is radioactive nuclear b-decay.
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This type of radioactivity was discovered in 1896 by A.A. Becquerelem. During the process of radioactive electron /b - -/ decay, one of the neutrons / n/ the atomic nucleus turns into a proton / R/ with electron emission / e-/ and electron antineutrino //:
n ® p + e-+
In the process of positronic /b + -/ decay the following transition occurs:
p® n + e++
In the first theory of b-decay, created in 1934 by E. Fermi, to explain this phenomenon it was necessary to introduce the hypothesis of the existence of a special type of short-range forces that cause the transition
n ® p + e-+
Further research showed that the interaction introduced by Fermi has a universal character.
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It causes the decay of all unstable particles, whose masses and selection rules based on quantum numbers do not allow them to decay due to strong or electromagnetic interaction. Weak interaction is inherent in all particles except photons. The characteristic time of weak interaction processes at energies of the order of 100 MeV is 13-14 orders of magnitude longer than the characteristic time for strong interaction.
The weak interaction quanta are three bosons - W + , W − , Z°- bosons. Superscripts indicate sign electric charge these quanta. The weak interaction quanta have a significant mass, which leads to the fact that the weak interaction manifests itself at very short distances.
It must be taken into account that today the weak and electromagnetic interactions are already combined into a single theory. There are a number of theoretical schemes that attempt to create a unified theory of all types of interaction. However, these schemes have not yet been developed enough to be tested experimentally.
26. Structural physics. Corpuscular approach to the description and explanation of nature. Reductionism
The objects of structural physics are the elements of the structure of matter (for example, molecules, atoms, elementary particles) and more complex education of them. This:
1) plasma - it is a gas in which a significant portion of the molecules or atoms are ionized;
2) crystals- This solids, in which atoms or molecules are arranged in an orderly manner and form a periodically repeating internal structure;
3) liquids- this is the aggregate state of a substance, which combines the features of a solid state (conservation of volume, a certain tensile strength) and a gaseous state (shape variability).
The liquid is characterized by:
a) short-range order in the arrangement of particles (molecules, atoms);
b) a small difference in the kinetic energy of thermal motion and their potential interaction energy.
4) stars,ᴛ.ᴇ. glowing gas (plasma) balls.
When identifying structural equations of a substance, the following criteria are used:
Spatial dimensions: particles of the same level have spatial dimensions of the same order (for example, all atoms have dimensions of the order of 10 -8 cm);
Process time: at one level it is approximately the same order of magnitude;
Objects of the same level consist of the same elements (for example, all nuclei consist of protons and neutrons);
The laws that explain processes at one level are qualitatively different from the laws that explain processes at another level;
Objects at different levels differ in their basic properties (for example, all atoms are electrically neutral, and all nuclei are positively electrically charged).
As new levels of structure and states of matter are discovered, the object domain of structural physics is expanding.
It must be taken into account that when solving specific physical problems, issues related to elucidating structure, interaction and motion are closely intertwined.
At the root of structural physics is a corpuscular approach to describing and explaining nature.
For the first time, the concept of the atom as the last and indivisible particle of the body arose in Ancient Greece within the framework of the natural philosophical teachings of the school of Leucippus-Democritus. According to this view, there are only atoms in the world that move in the void. The ancient atomists considered the continuity of matter to be apparent. Different combinations of atoms form different visible bodies. This hypothesis was not based on experimental data. She was just a brilliant guess. But it determined everything for many centuries to come. further development natural sciences.
The hypothesis of atoms as indivisible particles of matter was revived in natural science, in particular in physics and chemistry, to explain some laws that were established experimentally (for example, the Boyle-Mariotte and Gay-Lussac laws for ideal gases, thermal expansion tel, etc.). Indeed, the Boyle-Marriott law states that the volume of a gas is inversely proportional to its pressure, but it does not explain why this is so. Likewise, when a body is heated, its size increases. But what is the reason for this expansion? In the kinetic theory of matter, these and other experimentally established patterns are explained with the help of atoms and molecules.
Indeed, the directly observed and measurable decrease in gas pressure with an increase in its volume in the kinetic theory of matter is explained as an increase in the free path of its constituent atoms and molecules. It is as a result of this that the volume occupied by the gas increases. Similarly, the expansion of bodies when heated in the kinetic theory of matter is explained by an increase average speed moving molecules.
Explanations in which they try to reduce the properties of complex substances or bodies to the properties of their simpler elements or components, called reductionism. This method of analysis made it possible to solve a large class of problems in natural science.
Up to late XIX V. It was believed that an atom is the smallest, indivisible, structureless particle of matter. At the same time, the discoveries of the electron and radioactivity showed that this is not so. Rutherford's planetary model of the atom emerges. Then she is replaced by the model N. Bora. But as before, the thought of physicists is aimed at reducing the whole variety of complex properties of bodies and natural phenomena to simple properties a small number of primary particles. Subsequently, these particles were called elementary. Now their total number exceeds 350. For this reason, it is unlikely that all such particles can be called truly elementary, not containing other elements. This belief is strengthened by the hypothesis of the existence of quarks. According to it, known elementary particles consist of particles with fractional electric charges. They are called quarks.
According to the type of interaction in which elementary particles participate, all of them, except the photon, are classified into two groups:
1) hadrons. It is worth saying that they are characterized by the presence of strong interaction. Moreover, they can also participate in weak and electromagnetic interactions;
2) leptons. Οʜᴎ participate only in electromagnetic and weak interactions;
According to their lifespan, they are distinguished:
a) stable elementary particles. These are the electron, photon, proton and neutrino;
b) quasi-stable. These are particles that decay due to electromagnetic and weak interactions. For example, to + ® m + +;
c) unstable. Οʜᴎ decay due to strong interaction, for example, neutron.
The electric charges of elementary particles are multiples of the smallest charge inherent in the electron. At the same time, elementary particles are divided into particle – antiparticle pairs, for example e - - e + (they have all the same characteristics, and the signs of the electric charge are opposite). Electrically neutral particles also have antiparticles, for example, P -,- .
So, the atomistic concept is based on the idea of the discrete structure of matter. The atomistic approach explains the properties of a physical object based on the properties of its components tiny particles, which at a certain stage of cognition are considered indivisible. Historically, such particles were first recognized as atoms, then as elementary particles, and now as quarks. The difficulty of this approach is the complete reduction of the complex to the simple, which does not take into account the qualitative differences between them.
Until the end of the first quarter of the twentieth century, the idea of the unity of the structure of the macro- and microcosmos was understood mechanistically, as the complete identity of laws and as the complete similarity of the structure of both.
Microparticles were interpreted as miniature copies of macrobodies, ᴛ.ᴇ. as extremely small balls (corpuscles) moving in precise orbits that are completely similar to planetary orbits, with the only difference being that celestial bodies are bound by the forces of gravitational interaction, and microparticles by the forces of electrical interaction.
After the discovery of the electron (Thomson, 1897), the creation of the theory of quantum (Planck, 1900), and the introduction of the concept of photon (Einstein, 1905), atomic theory acquired a new character.
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The idea of discreteness was extended to the field of electrical and light phenomena, to the concept of energy (in the 19th century, the doctrine of energy served as the sphere of ideas about continuous quantities and functions of state). The most important feature of modern atomic teaching is the atomism of action. It is due to the fact that the movement, properties and states of various micro-objects are amenable to quantization, ᴛ.ᴇ. are expressed in the form of discrete quantities and ratios. New atomism recognizes the relative stability of each discrete type of matter, its qualitative certainty, its relative indivisibility and intransformability within the known boundaries of natural phenomena. For example, being divisible by some by physical means, the atom is indivisible chemically, ᴛ.ᴇ. V chemical processes he behaves as something whole, indivisible. A molecule, being divisible chemically into atoms, thermal movement(up to certain limits) behaves as a whole, indivisible, etc.
Particularly important in the concept of new atomism is the recognition of the interconvertibility of any discrete types of matter.
Different levels of the structural organization of physical reality (quarks, microparticles, nuclei, atoms, molecules, macrobodies, megasystems) have their own specific physical laws. But no matter how different the phenomena being studied are from the phenomena studied by classical physics, all experimental data must be described using classical concepts. There is a fundamental difference between the description of the behavior of the microobject being studied and the description of the action measuring instruments. This is the result of the fact that the action of measuring instruments, in principle, should be described in the language of classical physics, but the object under study may not be described by this language.
The corpuscular approach in explaining physical phenomena and processes has always been combined with the continuum approach since the emergence of interaction physics. It was expressed in the concept of the field and the disclosure of its role in physical interaction. The representation of the field as a flow of a certain kind of particles (quantum field theory) and the attribution of wave properties to any physical object (Louis de Broglie's hypothesis) brought together these two approaches to the analysis of physical phenomena.
Weak interaction - concept and types. Classification and features of the category "Weak interaction" 2017, 2018.
In 1896, French scientist Henri Becquerel discovered radioactivity in uranium. This was the first experimental signal about previously unknown forces of nature - weak interaction. We now know that the weak force is behind many familiar phenomena - for example, it is involved in some thermonuclear reactions that support the radiation of the Sun and other stars.
The name “weak” came to this interaction due to a misunderstanding - for example, for a proton it is 1033 times stronger than the gravitational interaction (see Gravity, This Unity of Nature). This is, rather, a destructive interaction, the only force of nature that does not hold the substance together, but only destroys it. One could also call it “unprincipled,” since in destruction it does not take into account the principles of spatial parity and temporal reversibility, which are observed by other forces.
The basic properties of the weak interaction became known back in the 1930s, mainly thanks to the work of the Italian physicist E. Fermi. It turned out that, unlike gravitational and electrical forces, weak forces have a very short range of action. In those years, it seemed that there was no radius of action at all - interaction took place at one point in space, and, moreover, instantly. This interaction is virtual (on a short time) converts each proton of the nucleus into a neutron, a positron into a positron and a neutrino, and each neutron into a proton, electron and antineutrino. In stable nuclei (see Atomic nucleus), these transformations remain virtual, like the virtual creation of electron-positron pairs or proton-antiproton pairs in a vacuum.
If the difference in the masses of nuclei that differ by one in charge is large enough, these virtual transformations become real, and the nucleus changes its charge by 1, emitting an electron and an antineutrino (electron decay) or a positron and a neutrino (positron decay). Neutrons have a mass that exceeds by approximately 1 MeV the sum of the masses of a proton and an electron. Therefore, a free neutron decays into a proton, an electron and an antineutrino, releasing an energy of approximately 1 MeV. The lifetime of a free neutron is approximately 10 minutes, although in a bound state, for example, in deuteron, which consists of a neutron and a proton, these particles live indefinitely.
A similar event occurs with the muon (see Peptons) - it decays into an electron, neutrino and antineutrino. Before decaying, a muon lives about c - much less than a neutron. Fermi's theory explained this by the difference in the masses of the particles involved. The more energy released during decay, the faster it goes. The release of energy during -decay is about 100 MeV, approximately 100 times greater than during the decay of a neutron. The lifetime of a particle is inversely proportional to the fifth power of this energy.
As it turned out in recent decades, the weak interaction is nonlocal, that is, it does not occur instantly and not at one point. According to modern theory, the weak interaction is not transmitted instantly, but a virtual electron-antineutrino pair is born s after the muon turns into a neutrino, and this happens at a distance of cm. Not a single ruler, not a single microscope can, of course, measure such a small distance, just as no stopwatch can measure such a small interval of time. As is almost always the case, in modern physics we must be content with indirect data. Physicists build various hypotheses about the mechanism of the process and test all sorts of consequences of these hypotheses. Those hypotheses that contradict at least one reliable experiment are discarded, and new experiments are carried out to test the remaining ones. This process, in the case of the weak interaction, continued for about 40 years, until physicists became convinced that the weak interaction was carried by supermassive particles - 100 times heavier than the proton. These particles have spin 1 and are called vector bosons (discovered in 1983 at CERN, Switzerland - France).
There are two charged vector bosons and one neutral one (the icon at the top, as usual, indicates the charge in proton units). A charged vector boson “works” in the decays of the neutron and muon. The course of muon decay is shown in Fig. (above, right). Such drawings are called Feynman diagrams; they not only illustrate the process, but also help to calculate it. This is a kind of shorthand for the formula for the probability of a reaction; it is used here for illustration purposes only.
The muon turns into a neutrino, emitting a -boson, which decays into an electron and an antineutrino. The released energy is not enough for the real birth of a -boson, so it is born virtually, i.e. for a very short time. IN in this case it with. During this time, the field corresponding to the -boson does not have time to form a wave, or otherwise, a real particle (see Fields and particles). A field clot of cm in size is formed, and after c an electron and an antineutrino are born from it.
For the decay of a neutron it would be possible to draw the same diagram, but here it would already mislead us. The fact is that the size of a neutron is cm, which is 1000 times greater than the radius of action of weak forces. Therefore, these forces act inside the neutron, where the quarks are located. One of the three neutron quarks emits a -boson, transforming into another quark. The charges of quarks in a neutron are: -1/3, - 1/3 and so one of the two quarks with a negative charge of -1/3 turns into a quark with a positive charge. The result will be quarks with charges - 1/3, 2/3, 2/3, which together make up a proton. The reaction products - electron and antineutrino - freely fly out of the proton. But it’s a quark that emitted a -boson. received the kickback and began to move in opposite direction. Why doesn't he fly out?
It is held together by a strong interaction. This interaction will carry the quark along with its two inseparable companions, resulting in a moving proton. According to a similar scheme, weak decays (associated with weak interaction) of the remaining hadrons occur. They all boil down to the emission of a vector boson by one of the quarks, the transition of this vector boson into leptons (, and -particles) and the further expansion of the reaction products.
Sometimes, however, hadronic decays also occur: a vector boson can decay into a quark-antiquark pair, which will turn into mesons.
So, a large number of of various reactions comes down to the interaction of quarks and leptons with vector bosons. This interaction is universal, that is, it is the same for quarks and leptons. The universality of the weak interaction, in contrast to the universality of gravitational or electromagnetic interaction, has not yet received a comprehensive explanation. In modern theories, the weak interaction is combined with the electromagnetic interaction (see Unity of the forces of nature).
On symmetry breaking by the weak interaction, see Parity, Neutrinos. The article The Unity of the Forces of Nature talks about the place of weak forces in the picture of the microworld
The weak force, or weak nuclear force, is one of the four fundamental forces in nature. It is responsible, in particular, for the beta decay of the nucleus. This interaction is called weak, since the other two interactions that are significant for nuclear physics (strong and electromagnetic) are characterized by much greater intensity. However, it is much stronger than the fourth of the fundamental interactions, gravitational. This interaction is the weakest of the fundamental interactions experimentally observed in the decays of elementary particles, where quantum effects are fundamentally significant. Quantum manifestations of gravitational interaction have never been observed. Weak interaction is distinguished using the following rule: if an elementary particle called a neutrino (or antineutrino) participates in the interaction process, then this interaction is weak.
A typical example of the weak interaction is the beta decay of a neutron
where n is a neutron, p is a proton, e- is an electron, e is an electron antineutrino.
It should, however, be borne in mind that the above rule does not mean at all that any act of weak interaction must be accompanied by a neutrino or antineutrino. It is known that a large number of neutrinoless decays occur. As an example, we can note the process of decay of a lambda hyperon into a p proton and a negatively charged pion. By modern ideas The neutron and proton are not true elementary particles, but are composed of elementary particles called quarks.
The intensity of the weak interaction is characterized by the Fermi coupling constant GF. The GF constant is dimensional. To form a dimensionless quantity, it is necessary to use some reference mass, for example the proton mass mp. Then the dimensionless coupling constant will be
It can be seen that the weak interaction is much more intense than the gravitational interaction.
The weak interaction, unlike the gravitational interaction, is short-range. This means that the weak force between particles only comes into play if the particles are close enough to each other. If the distance between particles exceeds a certain value called the characteristic radius of interaction, the weak interaction does not manifest itself. It has been experimentally established that the characteristic radius of weak interaction is about 10-15 cm, that is, weak interaction is concentrated at distances smaller than the size of the atomic nucleus. Although the weak interaction is significantly concentrated within the nucleus, it has certain macroscopic manifestations. In addition, the weak interaction plays an important role in the so-called thermonuclear reactions responsible for the mechanism of energy release in stars. The most amazing property of the weak interaction is the existence of processes in which mirror asymmetry is manifested. At first glance, it seems obvious that the difference between the concepts left and right is arbitrary. Indeed, the processes of gravitational, electromagnetic and strong interaction are invariant with respect to spatial inversion, which carries out mirror reflection. It is said that in such processes the spatial parity P is conserved. However, it has been experimentally established that weak processes can proceed with non-conservation of spatial parity and, therefore, seem to sense the difference between left and right. Currently, there is solid experimental evidence that parity nonconservation in weak interactions is universal in nature; it manifests itself not only in the decays of elementary particles, but also in nuclear and even atomic phenomena. It should be recognized that mirror asymmetry is a property of Nature at the most fundamental level.
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