An elementary particle is the smallest, indivisible, structureless particle.

FUNDAMENTALS OF ELECTRODYNAMICS

Electrodynamics– a branch of physics that studies electromagnetic interactions. Electromagnetic interactions– interactions of charged particles. The main objects of study in electrodynamics are electrical and magnetic fields created by electric charges and currents.

Topic 1. Electric field (electrostatics)

Electrostatics – a branch of electrodynamics that studies the interaction of stationary (static) charges.

Electric charge.

All bodies are electrified.

To electrify a body means to impart an electric charge to it.

Electrified bodies interact - they attract and repel.

The more electrified the bodies are, the stronger they interact.

Electric charge is physical quantity, which characterizes the property of particles or bodies to enter into electromagnetic interactions and is a quantitative measure of these interactions.

The totality of all known experimental facts allows us to draw the following conclusions:

· There are two types of electric charges, conventionally called positive and negative.

· Charges do not exist without particles

· Charges can be transferred from one body to another.

· Unlike body mass, electric charge is not an integral characteristic of a given body. The same body different conditions may have a different charge.

· Electric charge does not depend on the choice of reference system in which it is measured. Electric charge does not depend on the speed of the charge carrier.

· Like charges repel, unlike charges attract.

SI unit – pendant

An elementary particle is the smallest, indivisible, structureless particle.

For example, in an atom: electron ( , proton ( , neutron ( .

An elementary particle may or may not have a charge: , ,

Elementary charge-the charge belonging to an elementary particle is the smallest, indivisible.

Elementary charge – electron charge modulo.

The charges of an electron and a proton are numerically equal, but opposite in sign:

Electrification of bodies.
What does “a macroscopic body is charged” mean? What determines the charge of any body?

All bodies are made of atoms, which include positively charged protons, negatively charged electrons and neutral particles - neutrons . Protons and neutrons are part of atomic nuclei, electrons form the electron shell of atoms.

In a neutral atom, the number of protons in the nucleus is equal to the number of electrons in the shell.

Macroscopic bodies consisting of neutral atoms are electrically neutral.

An atom of a given substance may lose one or more electrons or gain an extra electron. In these cases, the neutral atom turns into a positively or negatively charged ion.

Electrification of bodies– the process of obtaining electrically charged bodies from electrically neutral ones.

Bodies become electrified upon contact with each other.

Upon contact, part of the electrons from one body passes to another, both bodies become electrified, i.e. receive charges equal in magnitude and opposite in sign:
an “excess” of electrons compared to protons creates a “-” charge in the body;
The “lack” of electrons compared to protons creates a “+” charge in the body.
The charge of any body is determined by the number of excess or insufficient electrons compared to protons.

Charge can be transferred from one body to another only in portions containing an integer number of electrons. Thus, the electric charge of a body is a discrete quantity that is a multiple of the electron charge:

Can you briefly and succinctly answer the question: “What is an electric charge?” This may seem simple at first glance, but in reality it turns out to be much more complicated.

Do we know what electric charge is?

The fact is that at the current level of knowledge we cannot yet decompose the concept of “charge” into simpler components. This is a fundamental, so to speak, primary concept.

We know that this is a certain property of elementary particles, the mechanism of interaction of charges is known, we can measure the charge and use its properties.

However, all this is a consequence of data obtained experimentally. The nature of this phenomenon is still not clear to us. Therefore, we cannot unambiguously determine what an electric charge is.

To do this, it is necessary to expand on a whole range of concepts. Explain the mechanism of interaction between charges and describe their properties. Therefore, it is easier to understand what the statement means: “this particle has (carries) an electric charge.”

The presence of an electric charge on a particle

However, later it was possible to establish that the number of elementary particles is much larger, and that the proton, electron and neutron are not indivisible and fundamental building materials of the Universe. They themselves can decompose into components and turn into other types of particles.

Therefore, the name "elementary particle" currently includes a fairly large class of particles smaller in size than atoms and atomic nuclei. In this case, particles can have a variety of properties and qualities.

However, such a property as electric charge comes in only two types, which are conventionally called positive and negative. The presence of a charge on a particle is its ability to repel or be attracted to another particle, which also carries a charge. The direction of interaction depends on the type of charges.

Like charges repel, unlike charges attract. Moreover, the force of interaction between charges is very large in comparison with the gravitational forces inherent in all bodies in the Universe without exception.

In the hydrogen nucleus, for example, an electron carrying a negative charge is attracted to a nucleus consisting of a proton and carrying a positive charge with a force 1039 times greater than the force with which the same electron is attracted by a proton due to gravitational interaction.

Particles may or may not carry a charge, depending on the type of particle. However, it is impossible to “remove” the charge from the particle, just as the existence of a charge outside the particle is impossible.

In addition to the proton and neutron, some other types of elementary particles carry a charge, but only these two particles can exist indefinitely.

719. Law of conservation of electric charge

720. Bodies with electric charges different sign, …

They are attracted to each other.

721. Identical metal balls, charged with opposite charges q 1 = 4q and q 2 = -8q, were brought into contact and moved apart to the same distance. Each of the balls has a charge

q 1 = -2q and q 2 = -2q

723.A droplet having a positive charge (+2e) lost one electron when illuminated. The charge of the drop became equal

724. Identical metal balls charged with charges q 1 = 4q, q 2 = - 8q and q 3 = - 2q were brought into contact and moved apart to the same distance. Each of the balls will have a charge

q 1 = - 2q, q 2 = - 2q and q 3 = - 2q

725. Identical metal balls charged with charges q 1 = 5q and q 2 = 7q were brought into contact and moved apart to the same distance, and then the second and third ball with charge q 3 = -2q were brought into contact and moved apart to the same distance. Each of the balls will have a charge

q 1 = 6q, q 2 = 2q and q 3 = 2q

726. Identical metal balls charged with charges q 1 = - 5q and q 2 = 7q were brought into contact and moved apart to the same distance, and then the second and third ball with charge q 3 = 5q were brought into contact and moved apart to the same distance. Each of the balls will have a charge

q 1 =1q, q 2 = 3q and q 3 = 3q

727. There are four identical metal balls with charges q 1 = 5q, q 2 = 7q, q 3 = -3q and q 4 = -1q. First, the charges q 1 and q 2 (1st system of charges) were brought into contact and moved apart to the same distance, and then the charges q 4 and q 3 (2nd system of charges) were brought into contact. Then they took one charge each from system 1 and 2 and brought them into contact and moved them apart to the same distance. These two balls will have a charge

728. There are four identical metal balls with charges q 1 = -1q, q 2 = 5q, q 3 = 3q and q 4 = -7q. First, the charges q 1 and q 2 (1 system of charges) were brought into contact and moved apart to the same distance, and then the charges q 4 and q 3 (system 2 of charges) were brought into contact. Then they took one charge each from system 1 and 2 and brought them into contact and moved them apart to the same distance. These two balls will have a charge

729.An atom has a positive charge

Core.

730.8 electrons move around the nucleus of an oxygen atom. The number of protons in the nucleus of an oxygen atom is

731.The electric charge of an electron is

-1.6 · 10 -19 Cl.

732.The electric charge of a proton is

1.6 · 10 -19 Cl.

733.The nucleus of a lithium atom contains 3 protons. If 3 electrons rotate around the nucleus, then

The atom is electrically neutral.

734. There are 19 particles in the fluorine nucleus, of which 9 are protons. The number of neutrons in the nucleus and the number of electrons in a neutral fluorine atom

Neutrons and 9 electrons.

735.If in any body the number of protons more number electrons, then the body as a whole

Positively charged.

736. A droplet having a positive charge of +3e lost 2 electrons when irradiated. The charge of the drop became equal

8·10 -19 Cl.

737. A negative charge in an atom carries

Shell.

738.If an oxygen atom turns into a positive ion, then it

Lost an electron.

739.Has a large mass

Negative hydrogen ion.

740. As a result of friction, 5·10 10 electrons were removed from the surface of a glass rod. Electric charge on a stick

(e = -1.6 10 -19 C)

8·10 -9 Cl.

741.As a result of friction, the ebonite rod received 5·10 10 electrons. Electric charge on a stick

(e = -1.6 10 -19 C)

-8·10 -9 Cl.

742.The force of the Coulomb interaction of two point electric charges when the distance between them decreases by 2 times

Will increase 4 times.

743.The force of the Coulomb interaction of two point electric charges when the distance between them decreases by 4 times

Will increase 16 times.

744.Two point electric charges act on each other according to Coulomb’s law with a force of 1N. If the distance between them is increased by 2 times, then the force of the Coulomb interaction of these charges will become equal

745.Two point charges act on each other with a force of 1N. If the magnitude of each charge is increased by 4 times, then the strength of the Coulomb interaction will become equal

746. The force of interaction between two point charges is 25 N. If the distance between them is reduced by 5 times, then the force of interaction of these charges will become equal

747.The force of the Coulomb interaction of two point charges when the distance between them increases by 2 times

Will decrease by 4 times.

748.The force of the Coulomb interaction of two point electric charges when the distance between them increases by 4 times

Will decrease by 16 times.

749. Formula of Coulomb's law

.

750. If 2 identical metal balls having charges +q and +q are brought into contact and moved apart to the same distance, then the modulus of the interaction force

Will not change.

751. If 2 identical metal balls having charges +q and -q, the balls are brought into contact and moved apart to the same distance, then the interaction force

Will become equal to 0.

752.Two charges interact in the air. If they are placed in water (ε = 81), without changing the distance between them, then the force of the Coulomb interaction

Will decrease by 81 times.

753.The force of interaction between two charges of 10 nC each, located in the air at a distance of 3 cm from each other, is equal to

()

754. Charges of 1 µC and 10 nC interact in air with a force of 9 mN at a distance

()

755. Two electrons located at a distance of 3·10 -8 cm from each other repel with a force ( ; e = - 1.6 10 -19 C)

2.56·10 -9 N.

756. When the distance from the charge increases by 3 times, the voltage module electric field

Will decrease by 9 times.

757.The field strength at a point is 300 N/C. If the charge is 1·10 -8 C, then the distance to the point

()

758. If the distance from a point charge creating an electric field increases 5 times, then the electric field strength

Will decrease by 25 times.

759.The field strength of a point charge at a certain point is 4 N/C. If the distance from the charge is doubled, the voltage will become equal to

760.Indicate the formula for the electric field strength in the general case.

761.Mathematical notation of the principle of superposition of electric fields

762.Indicate the formula for the intensity of a point electric charge Q

.

763. Electric field strength modulus at the point where the charge is located

1·10 -10 C is equal to 10 V/m. The force acting on the charge is equal to

1·10 -9 N.

765. If a charge of 4·10 -8 C is distributed on the surface of a metal ball with a radius of 0.2 m, then the charge density

2.5·10 -7 C/m2.

766.In a vertically directed homogeneous electric field there is a speck of dust with a mass of 1·10-9 g and a charge of 3.2·10-17 C. If the gravity of a dust grain is balanced by the strength of the electric field, then the field strength is equal to

3·10 5 N/Cl.

767. At the three vertices of a square with a side of 0.4 m there are identical positive charges of 5·10 -9 C each. Find the tension at the fourth vertex

() 540 N/Cl.

768. If two charges are 5·10 -9 and 6·10 -9 C, so that they repel with a force of 12·10 -4 N, then they are at a distance

768. If the module of a point charge is reduced by 2 times and the distance to the charge is reduced by 4 times, then the electric field strength at a given point

Will increase 8 times.

Decreases.

770. The product of the electron charge and the potential has the dimension

Energy.

771.The potential at point A of the electric field is 100V, the potential at point B is 200V. The work done by the electric field forces when moving a charge of 5 mC from point A to point B is equal to

-0.5 J.

772. A particle with charge +q and mass m, located at points of an electric field with intensity E and potential, has acceleration

773.An electron moves in a uniform electric field along a line of tension from a point with a high potential to a point with a lower potential. Its speed is

Increasing.

774.An atom that has one proton in its nucleus loses one electron. This creates

Hydrogen ion.

775. An electric field in a vacuum is created by four point positive charges, placed at the vertices of the square with side a. The potential at the center of the square is

776. If the distance from a point charge decreases by 3 times, then the field potential

Will increase 3 times.

777. When a point electric charge q moves between points with a potential difference of 12 V, 3 J of work is done. In this case, the charge is moved

778. Charge q moved from point electrostatic field to a point with potential. By which of the following formulas:

1) 2) ; 3) you can find work moving charge.

779. In a uniform electric field of strength 2 N/C, a charge of 3 C moves along the field lines at a distance of 0.5 m. The work done by the electric field forces to move the charge is equal to

780.The electric field is created by four point unlike charges placed at the vertices of a square with side a. Like charges are located at opposite vertices. The potential at the center of the square is

781. Potential difference between points lying on the same power line at a distance of 6 cm from each other, is equal to 60 V. If the field is uniform, then its strength is

782.Unit of potential difference

1 V = 1 J/1 C.

783. Let the charge move in a uniform field with intensity E = 2 V/m along a field line of 0.2 m. Find the difference between these potentials.

U = 0.4 V.

784.According to Planck's hypothesis, a completely black body emits energy

In portions.

785. Photon energy is determined by the formula

1. E =pс 2. E=hv/c 3. E=h 4. E=mc2. 5. E=hv. 6.E=hc/

1, 4, 5, 6.

786. If the energy of a quantum has doubled, then the frequency of the radiation

increased by 2 times.

787.If photons with an energy of 6 eV fall on the surface of a tungsten plate, then the maximum kinetic energy of the electrons knocked out by them is 1.5 eV. The minimum photon energy at which the photoelectric effect is possible is for tungsten equal to:

788.The following statement is correct:

1. The speed of a photon is greater than the speed of light.

2. The speed of a photon in any substance is less than the speed of light.

3. The speed of a photon is always equal to the speed of light.

4. The speed of a photon is greater than or equal to the speed of light.

5. The speed of a photon in any substance is less than or equal to the speed of light.

789.Radiation photons have a large impulse

Blue.

790. When the temperature of a heated body decreases, the maximum radiation intensity

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Further 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 19th century. the electron was discovered, and then in the first decades of the 20th century. – 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 was established - over 300. Among them there are both experimentally discovered and theoretically calculated, including resonances, quarks and virtual particles.

Term elementary particle originally meant the simplest, further indecomposable particles that underlie any material formations. Later, physicists realized the entire convention of the term “elementary” in relation to micro-objects. Now there is no doubt that particles have one structure or another, but, nevertheless, the historically established name continues to exist.

The main characteristics of elementary particles are mass, charge, average lifetime, spin and quantum numbers.

Resting mass elementary particles are determined in relation to the rest mass of the electron. There are elementary particles that do not have a rest mass - photons. The remaining particles according to this criterion are divided into leptons– light particles (electron and neutrino); mesons– medium-sized particles with a mass ranging from one to a thousand electron masses; baryons– heavy particles whose mass exceeds a thousand electron masses and which includes 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 the photon and two mesons, corresponds to antiparticles with opposite charges. Around 1963–1964 a hypothesis was put forward about the existence quarks– particles with a fractional electric charge. This hypothesis has not yet been confirmed experimentally.

By lifetime particles are divided into stable And unstable . There are five stable particles: the photon, two types of neutrinos, the electron and the 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 10–23–10–22 s are called resonances. Due to their short lifetime, they decay before they even leave the atom or atomic nucleus. Resonant states were calculated theoretically; they could not be detected 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 . Spin is the intrinsic angular momentum of a particle that is not associated with its movement. Spin is characterized by spin quantum number s, which can take integer (±1) or half-integer (±1/2) values. Particles with integer spin – bosons, with a half-integer – fermions. Electrons are classified as fermions. According to the Pauli principle, an atom cannot have more than one electron with the same set of quantum numbers n,m,l,s. Electrons, which correspond to wave functions with the same number n, are very close in energy and form an electron shell in the atom. Differences in the number l determine the “subshell”, the remaining quantum numbers determine its filling, as mentioned above.

In the characteristics of elementary particles there is another important idea interaction. As noted earlier, four types of interactions between elementary particles are known: gravitational,weak,electromagnetic And strong(nuclear).

All particles having a rest mass ( m 0), participate in gravitational interaction, and charged ones also participate in electromagnetic interaction. Leptons also participate in weak interactions. Hadrons participate in all four fundamental interactions.

According to quantum field theory, all interactions are carried out due to the exchange virtual particles , that is, particles whose existence can only be judged indirectly, by some of their manifestations through some secondary effects ( real particles can be directly recorded using instruments).

It turns out that all four known types of interactions - gravitational, electromagnetic, strong and weak - have a gauge nature and are described by gauge symmetries. That is, all interactions are, as it were, made “from the same blank.” This gives us hope that it will be possible to find “the only key to all known locks” and describe the evolution of the Universe from a state represented by a single supersymmetric superfield, from a state in which the differences between the types of interactions, between all kinds of particles of matter and field quanta have not yet appeared.

There are a huge number of ways to classify elementary particles. For example, particles are divided into fermions (Fermi particles) - particles of matter and bosons (Bose particles) - field quanta.

According to another approach, particles are divided into 4 classes: photons, leptons, mesons, baryons.

Photons (electromagnetic field quanta) participate in electromagnetic interactions, but do not have strong, weak, or gravitational interactions.

Leptons got their name from Greek word leptos- easy. These include particles that do not have strong interaction: muons (μ – , μ +), electrons (е – , у +), electron neutrinos (v e – ,v e +) and muon neutrinos (v – m, v + m). All leptons have a spin of ½ and are therefore fermions. All leptons have a weak interaction. Those that have an electrical charge (that is, muons and electrons) also have an electromagnetic force.

Mesons – strongly interacting unstable particles that do not carry the so-called baryon charge. Among them is R-mesons, or pions (π + , π – , π 0), TO-mesons, or kaons (K +, K –, K 0), and this-mesons (η) . Weight TO-mesons is ~970me (494 MeV for charged and 498 MeV for neutral TO-mesons). Lifetime TO-mesons has a magnitude of the order of 10 –8 s. They disintegrate to form I-mesons and leptons or only leptons. Weight this-mesons is 549 MeV (1074me), the lifetime is about 10–19 s. This-mesons decay to form π-mesons and γ-photons. Unlike leptons, mesons have not only a weak (and, if they are charged, electromagnetic) interaction, but also a strong interaction, which manifests itself when they interact with each other, as well as during the interaction between mesons and baryons. All mesons have zero spin, so they are bosons.

Class baryons combines nucleons (p,n) and unstable particles with a mass greater than the mass of nucleons, called hyperons. All baryons have a strong interaction and, therefore, actively interact with atomic nuclei. The spin of all baryons is ½, so the baryons are fermions. With the exception of the proton, all baryons are unstable. During the decay of baryons, along with other particles, a baryon is necessarily formed. This pattern is one of the manifestations baryon charge conservation law.

In addition to the particles listed above, a large number of strongly interacting short-lived particles have been discovered, which are called resonances . These particles are resonant states formed by two or more elementary particles. The resonance lifetime is only ~ 10 –23 –10 –22 s.

Elementary particles, as well as complex microparticles, can be observed thanks to the traces that they leave as they pass through matter. The nature of the traces allows us to judge the sign of the particle’s charge, its energy, momentum, etc. Charged particles cause ionization of molecules along their path. Neutral particles do not leave traces, but they can reveal themselves at the moment of decay into charged particles or at the moment of collision with any nucleus. Consequently, neutral particles are ultimately also detected by the ionization caused by the charged particles they generate.

Particles and antiparticles. In 1928, the English physicist P. Dirac managed to find a relativistic quantum mechanical equation for the electron, from which a number of remarkable consequences follow. First of all, from this equation the spin and numerical value of the electron’s own magnetic moment are obtained naturally, without any additional assumptions. Thus, it turned out that spin is both a quantum and a relativistic quantity. But this does not exhaust the significance of the Dirac equation. It also made it possible to predict the existence of the electron’s antiparticle – positron. From the Dirac equation, not only positive but also negative values ​​are obtained for the total energy of a free electron. Studies of the equation show that for a given particle momentum, there are solutions to the equation corresponding to the energies: .

Between the greatest negative energy (– m e With 2) and the least positive energy (+ m e c 2) there is an interval of energy values ​​that cannot be realized. The width of this interval is 2 m e With 2. Consequently, two regions of energy eigenvalues ​​are obtained: one begins with + m e With 2 and extends to +∞, the other starts from – m e With 2 and extends to –∞.

A particle with negative energy must have very strange properties. Transitioning into states with less and less energy (that is, with negative energy increasing in magnitude), it could release energy, say, in the form of radiation, and, since | E| unconstrained, a particle with negative energy could emit an infinitely large amount of energy. A similar conclusion can be reached in the following way: from the relation E=m e With 2 it follows that a particle with negative energy will also have a negative mass. Under the influence of a braking force, a particle with a negative mass should not slow down, but accelerate, performing an infinitely large amount of work on the source of the braking force. In view of these difficulties, it would seem that it would be necessary to admit that the state with negative energy should be excluded from consideration as leading to absurd results. This, however, would contradict some general principles of quantum mechanics. Therefore, Dirac chose a different path. He proposed that transitions of electrons to states with negative energy are usually not observed for the reason that all available levels with negative energy are already occupied by electrons.

According to Dirac, a vacuum is a state in which all levels of negative energy are occupied by electrons, and levels with positive energy are free. Since all levels lying below the forbidden band are occupied without exception, electrons at these levels do not reveal themselves in any way. If one of the electrons located at negative levels is given energy E≥ 2m e With 2, then this electron will go into a state with positive energy and will behave in the usual way, like a particle with positive mass and negative charge. This first theoretically predicted particle was called the positron. When a positron meets an electron, they annihilate (disappear) - the electron moves from a positive level to a vacant negative one. The energy corresponding to the difference between these levels is released in the form of radiation. In Fig. 4, arrow 1 depicts the process of creation of an electron-positron pair, and arrow 2 – their annihilation. The term “annihilation” should not be taken literally. Essentially, what occurs is not a disappearance, but a transformation of some particles (electron and positron) into others (γ-photons).

There are particles that are identical with their antiparticles (that is, they do not have antiparticles). Such particles are called absolutely neutral. These include the photon, π 0 meson and η meson. Particles identical with their antiparticles are not capable of annihilation. This, however, does not mean that they cannot turn into other particles at all.

If baryons (that is, nucleons and hyperons) are assigned a baryon charge (or baryon number) IN= +1, antibaryons – baryon charge IN= –1, and all other particles have a baryon charge IN= 0, then all processes occurring with the participation of baryons and antibaryons will be characterized by conservation of charge baryons, just as processes are characterized by conservation of electric charge. The law of conservation of baryon charge determines the stability of the softest baryon, the proton. The transformation of all quantities that describe a physical system, in which all particles are replaced by antiparticles (for example, electrons with protons, and protons with electrons, etc.), is called the conjugation charge.

Strange particles.TO-mesons and hyperons were discovered as part of cosmic rays in the early 50s of the XX century. Since 1953, they have been produced at accelerators. The behavior of these particles turned out to be so unusual that they were called strange. The unusual behavior of the strange particles was that they were clearly born due to strong interactions with a characteristic time of the order of 10–23 s, and their lifetimes turned out to be of the order of 10–8–10–10 s. The latter circumstance indicated that the decay of particles occurs as a result of weak interactions. It was completely unclear why the strange particles lived for so long. Since the same particles (π-mesons and protons) are involved in both the creation and decay of the λ-hyperon, it was surprising that the rate (that is, the probability) of both processes was so different. Further research showed that strange particles are born in pairs. This led to the idea that strong interactions cannot play a role in particle decay due to the fact that the presence of two strange particles is necessary for their manifestation. For the same reason, the single creation of strange particles turns out to be impossible.

To explain the prohibition of the single production of strange particles, M. Gell-Mann and K. Nishijima introduced a new quantum number, the total value of which, according to their assumption, should be conserved under strong interactions. This is a quantum number S was named the strangeness of the particle. In weak interactions, the strangeness may not be preserved. Therefore, it is attributed only to strongly interacting particles - mesons and baryons.

Neutrino. Neutrino is the only particle that does not participate in either strong or electromagnetic interactions. Excluding the gravitational interaction, in which all particles participate, neutrinos can only take part in weak interactions.

For a long time, it remained unclear how a neutrino differs from an antineutrino. The discovery of the law of conservation of combined parity made it possible to answer this question: they differ in helicity. Under helicity a certain relationship between the directions of the impulse is understood R and back S particles. Helicity is considered positive if spin and momentum are in the same direction. In this case, the direction of particle motion ( R) and the direction of “rotation” corresponding to the spin form a right-handed screw. When the spin and momentum are oppositely directed, the helicity will be negative (the translational movement and “rotation” form a left-handed screw). According to the theory of longitudinal neutrinos developed by Yang, Lee, Landau and Salam, all neutrinos existing in nature, regardless of the method of their origin, are always completely longitudinally polarized (that is, their spin is directed parallel or antiparallel to the momentum R). Neutrino has negative(left) helicity (corresponding to the ratio of directions S And R, shown in Fig. 5 (b), antineutrino – positive (right-handed) helicity (a). Thus, helicity is what distinguishes neutrinos from antineutrinos.

Rice. 5. Scheme of helicity of elementary particles

Systematics of elementary particles. The patterns observed in the world of elementary particles can be formulated in the form of conservation laws. Quite a lot of such laws have already accumulated. Some of them turn out to be not exact, but only approximate. Each conservation law expresses a certain symmetry of the system. Laws of conservation of momentum R, angular momentum L and energy E reflect the properties of symmetry of space and time: conservation E is a consequence of the homogeneity of time, the preservation R due to the homogeneity of space, and the preservation L– its isotropy. The law of conservation of parity is associated with the symmetry between right and left ( R-invariance). Symmetry with respect to charge conjugation (symmetry of particles and antiparticles) leads to the conservation of charge parity ( WITH-invariance). The laws of conservation of electric, baryon and lepton charges express a special symmetry WITH-functions. Finally, the law of conservation of isotopic spin reflects the isotropy of isotopic space. Failure to comply with one of the conservation laws means a violation of the corresponding type of symmetry in this interaction.

In the world of elementary particles there is a rule: everything that is not prohibited by conservation laws is permitted. The latter play the role of exclusion rules governing the interconversion of particles. First of all, let us note the laws of conservation of energy, momentum and electric charge. These three laws explain the stability of the electron. From the conservation of energy and momentum it follows that the total rest mass of the decay products must be less than the rest mass of the decaying particle. This means that an electron could only decay into neutrinos and photons. But these particles are electrically neutral. So it turns out that the electron simply has no one to transfer its electric charge to, so it is stable.

Quarks. There have become so many particles called elementary that serious doubts have arisen about their elementary nature. Each of the strongly interacting particles is characterized by three independent additive quantum numbers: charge Q, hypercharge U and baryon charge IN. In this regard, a hypothesis arose that all particles are built from three fundamental particles - carriers of these charges. In 1964, Gell-Mann and, independently of him, the Swiss physicist Zweig put forward a hypothesis according to which all elementary particles are built from three particles called quarks. These particles are assigned fractional quantum numbers, in particular, an electric charge equal to +⅔; –⅓; +⅓ respectively for each of the three quarks. These quarks are usually designated by the letters U,D,S. In addition to quarks, antiquarks are considered ( u,d,s). To date, 12 quarks are known - 6 quarks and 6 antiquarks. Mesons are formed from a quark-antiquark pair, and baryons are formed from three quarks. For example, a proton and a neutron are composed of three quarks, which makes the proton or neutron colorless. Accordingly, three charges of strong interactions are distinguished - red ( R), yellow ( Y) and green ( G).

Each quark is assigned the same magnetic moment (μV), the value of which is not determined from theory. Calculations made on the basis of this assumption give the value of the magnetic moment μ p for the proton = μ kv, and for a neutron μ n = – ⅔μ sq.

Thus, for the ratio of magnetic moments the value μ p is obtained / μn = –⅔, in excellent agreement with the experimental value.

Basically, the color of the quark (like the sign of the electric charge) began to express the difference in the property that determines the mutual attraction and repulsion of quarks. By analogy with quanta of fields of various interactions (photons in electromagnetic interactions, R-mesons in strong interactions, etc.) particles that carried the interaction between quarks were introduced. These particles were named gluons. They transfer color from one quark to another, causing the quarks to be held together. In quark physics, the confinement hypothesis was formulated (from the English. confinements– capture) of quarks, according to which it is impossible to subtract a quark from the whole. It can only exist as an element of the whole. The existence of quarks as real particles in physics is reliably substantiated.

The idea of ​​quarks turned out to be very fruitful. It made it possible not only to systematize already known particles, but also to predict a whole series of new ones. The situation that has developed in the physics of elementary particles is reminiscent of the situation created in atomic physics after the discovery of the periodic law in 1869 by D. I. Mendelev. Although the essence of this law was clarified only about 60 years after the creation of quantum mechanics, it made it possible to systematize the chemical elements known by that time and, in addition, led to the prediction of the existence of new elements and their properties. In the same way, physicists have learned to systematize elementary particles, and the developed taxonomy in a number of cases made it possible to predict the existence of new particles and anticipate their properties.

So, at present, quarks and leptons can be considered truly elementary; There are 12 of them, or together with anti-chatits - 24. In addition, there are particles that provide four fundamental interactions (interaction quanta). There are 13 of these particles: graviton, photon, W± - and Z-particles and 8 gluons.

Existing theories of elementary particles cannot indicate what is the beginning of the series: atoms, nuclei, hadrons, quarksIn this series, each more complex material structure includes a simpler one as component. Apparently, this cannot continue indefinitely. It was assumed that the described chain of material structures is based on objects of a fundamentally different nature. It is shown that such objects may not be pointlike, but extended, albeit extremely small (~10‑33 cm) formations, called superstrings. The described idea is not realizable in our four-dimensional space. This area of ​​physics is generally extremely abstract, and it is very difficult to find visual models that help simplify the perception of the ideas inherent in the theories of elementary particles. Nevertheless, these theories allow physicists to express the mutual transformation and interdependence of the “most elementary” micro-objects, their connection with the properties of four-dimensional space-time. The most promising is the so-called M-theory (M – from mystery- riddle, secret). She's operating twelve-dimensional space . Ultimately, during the transition to the four-dimensional world that we directly perceive, all “extra” dimensions are “collapsed.” M-theory is so far the only theory that makes it possible to reduce four fundamental interactions to one - the so-called Superpower. It is also important that M-theory allows for the existence of different worlds and establishes the conditions that ensure the emergence of our world. M-theory is not yet sufficiently developed. It is believed that the final "theory of everything" based on M-theory will be built in the 21st century.

From approximately 1000 seconds (for a free neutron) to a negligible fraction of a second (from 10 −24 to 10 −22 s for resonances).

The structure and behavior of elementary particles is studied by particle physics.

All elementary particles are subject to the principle of identity (all elementary particles of the same type in the Universe are completely identical in all their properties) and the principle of particle-wave dualism (each elementary particle corresponds to a de Broglie wave).

All elementary particles have the property of interconvertibility, which is a consequence of their interactions: strong, electromagnetic, weak, gravitational. Particle interactions cause transformations of particles and their collections into other particles and their collections, if such transformations are not prohibited by the laws of conservation of energy, momentum, angular momentum, electric charge, baryon charge, etc.

Main characteristics of elementary particles: lifetime, mass, spin, electric charge, magnetic moment, baryon charge, lepton charge, strangeness, isotopic spin, parity, charge parity, G-parity, CP-parity.

Classification

By lifetime

• Stable elementary particles are particles that have an infinitely long lifetime in a free state (proton, electron, neutrino, photon and their antiparticles).
• Unstable elementary particles are particles that decay into other particles in a free state in a finite time (all other particles).

By weight

All elementary particles are divided into two classes:

• Massless particles are particles with zero mass (photon, gluon).
• Particles with non-zero mass (all other particles).

By largest back

All elementary particles are divided into two classes:

By type of interaction

Elementary particles are divided into the following groups:

Compound particles

• Hadrons are particles that participate in all types of fundamental interactions. They consist of quarks and are divided, in turn, into:
  • mesons are hadrons with integer spin, that is, they are bosons;
  • baryons are hadrons with half-integer spin, that is, fermions. These, in particular, include the particles that make up the nucleus of an atom - proton and neutron.

Fundamental (structureless) particles

• Leptons are fermions that have the form of point particles (that is, not consisting of anything) up to scales of the order of 10 −18 m. They do not participate in strong interactions. Participation in electromagnetic interactions was experimentally observed only for charged leptons (electrons, muons, tau leptons) and was not observed for neutrinos. There are 6 known types of leptons.
• Quarks are fractionally charged particles that are part of hadrons. They were not observed in the free state (a confinement mechanism has been proposed to explain the absence of such observations). Like leptons, they are divided into 6 types and are considered structureless, however, unlike leptons, they participate in strong interactions.
• Gauge bosons are particles through the exchange of which interactions are carried out:
  • photon is a particle that carries electromagnetic interaction;
  • eight gluons - particles that carry the strong force;
  • three intermediate vector bosons W + , W− and Z 0, which tolerate weak interaction;
  • graviton is a hypothetical particle that carries the gravitational force. The existence of gravitons, although not yet experimentally proven due to the weakness of gravitational interaction, is considered quite probable; however, the graviton is not included in the Standard Model of elementary particles.

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Sizes of elementary particles

Despite the wide variety of elementary particles, their sizes fit into two groups. The sizes of hadrons (both baryons and mesons) are about 10 −15 m, which is close to the average distance between the quarks included in them. The sizes of fundamental, structureless particles - gauge bosons, quarks and leptons - within the experimental error are consistent with their point nature (the upper limit of the diameter is about 10 −18 m) ( see explanation). If in further experiments the final sizes of these particles are not discovered, then this may indicate that the sizes of gauge bosons, quarks and leptons are close to the fundamental length (which very likely may turn out to be the Planck length equal to 1.6 10 −35 m) .

It should be noted, however, that the size of an elementary particle is a rather complex concept that is not always consistent with classical concepts. Firstly, the uncertainty principle does not allow one to strictly localize a physical particle. A wave packet, which represents a particle as a superposition of precisely localized quantum states, always has finite dimensions and a certain spatial structure, and the dimensions of the packet can be quite macroscopic - for example, an electron in an experiment with interference on two slits “feels” both slits of the interferometer, separated by a macroscopic distance . Secondly, a physical particle changes the structure of the vacuum around itself, creating a “coat” of short-term virtual particles - fermion-antifermion pairs (see Vacuum polarization) and bosons that carry interactions. The spatial dimensions of this region depend on the gauge charges possessed by the particle and on the masses of the intermediate bosons (the radius of the shell of massive virtual bosons is close to their Compton wavelength, which, in turn, is inversely proportional to their mass). Thus, the radius of an electron from the point of view of neutrinos (only weak interaction is possible between them) is approximately equal to the Compton wavelength of W-bosons, ~3 × 10 −18 m, and the dimensions of the region of strong interaction of the hadron are determined by the Compton wavelength of the lightest of hadrons, the pi-meson (~10 −15 m), acting here as a carrier of interaction.

Story

Initially, the term “elementary particle” meant something absolutely elementary, the first brick of matter. However, when hundreds of hadrons with similar properties were discovered in the 1950s and 1960s, it became clear that at least hadrons have internal degrees freedom, that is, they are not elementary in the strict sense of the word. This suspicion was later confirmed when it turned out that hadrons consist of quarks.

Thus, physicists have moved a little deeper into the structure of matter: leptons and quarks are now considered the most elementary, point-like parts of matter. For them (together with gauge bosons) the term “ fundamental particles".

In string theory, which has been actively developed since around the mid-1980s, it is assumed that elementary particles and their interactions are consequences various types vibrations of especially small “strings”.

Standard model

The Standard Model of elementary particles includes 12 flavors of fermions, their corresponding antiparticles, as well as gauge bosons (photons, gluons, W- And Z-bosons), which carry interactions between particles, and the Higgs boson, discovered in 2012, which is responsible for the presence of inertial mass in particles. However, the Standard Model is largely viewed as a temporary theory rather than a truly fundamental one, since it does not include gravity and contains several dozen free parameters (particle masses, etc.), the values ​​of which do not follow directly from the theory. Perhaps there are elementary particles that are not described by the Standard Model - for example, such as the graviton (a particle that hypothetically carries gravitational forces) or supersymmetric partners of ordinary particles. In total, the model describes 61 particles.

Fermions

The 12 flavors of fermions are divided into 3 families (generations) of 4 particles each. Six of them are quarks. The other six are leptons, three of which are neutrinos, and the remaining three carry a unit negative charge: the electron, muon, and tau lepton.

Generations of particles

First generation	Second generation	Third generation
Electron: e−	Muon: μ −	Tau lepton: τ −
Electron neutrino: ν e	Muon neutrino: ν μ	Tau neutrino: ν τ (\displaystyle \nu _(\tau ))
u-quark (“up”): u	c-quark (“charmed”): c	t-quark (“true”): t
d-quark (“down”): d	s-quark (“strange”): s	b-quark (“lovely”): b

Antiparticles

There are also 12 fermionic antiparticles corresponding to the above twelve particles.

Antiparticles

First generation	Second generation	Third generation
positron: e+	Positive muon: μ +	Positive tau lepton: τ +
Electron antineutrino: ν ¯ e (\displaystyle (\bar (\nu ))_(e))	Muon antineutrino: ν ¯ μ (\displaystyle (\bar (\nu ))_(\mu ))	Tau antineutrino: ν ¯ τ (\displaystyle (\bar (\nu ))_(\tau ))
u-antique: u ¯ (\displaystyle (\bar (u)))	c-antique: c ¯ (\displaystyle (\bar (c)))	t-antique: t ¯ (\displaystyle (\bar (t)))
d-antique: d ¯ (\displaystyle (\bar (d)))	s-antique: s ¯ (\displaystyle (\bar (s)))	b-antique: b ¯ (\displaystyle (\bar (b)))

Quarks

Quarks and antiquarks have never been discovered in a free state - this is explained by the phenomenon