Fundamental particle. In simple language about elementary particles, the collider and the God particle. The fundamental characteristic of the particle model is
Leptons do not participate in the strong interaction. electron. positron. muon. neutrino is a light neutral particle that participates only in weak and gravitational interactions. neutrino (# flux). quarks. carriers of interactions: photon quantum of light...
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electron - ▲ fundamental particle having, element, charge electron negatively charged elementary particle with elementary electric charge. ↓ … Ideographic Dictionary of the Russian Language
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A type of fundamental interactions (along with gravitational, weak and strong), which is characterized by the participation of an electromagnetic field (See Electromagnetic field) in interaction processes. Electromagnetic field (in quantum physics... ... Great Soviet Encyclopedia
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These three particles (as well as others described below) are mutually attracted and repelled according to their charges, of which there are only four types according to the number of fundamental forces of nature. The charges can be arranged in decreasing order of the corresponding forces as follows: color charge (forces of interaction between quarks); electric charge (electric and magnetic forces); weak charge (forces in some radioactive processes); finally, mass (gravitational force, or gravitational interaction). The word "color" here has nothing to do with the color of visible light; it is simply a characteristic of a strong charge and the greatest forces.
Charges are saved, i.e. the charge entering the system is equal to the charge leaving it. If the total electric charge of a certain number of particles before their interaction is equal to, say, 342 units, then after the interaction, regardless of its result, it will be equal to 342 units. This also applies to other charges: color (strong interaction charge), weak and mass (mass). Particles differ in their charges: in essence, they “are” these charges. Charges are like a “certificate” of the right to respond to the appropriate force. Thus, only colored particles are affected by color forces, only electrically charged particles are affected by electric forces, etc. The properties of a particle are determined by the greatest force acting on it. Only quarks are carriers of all charges and, therefore, are subject to the action of all forces, among which the dominant one is color. Electrons have all charges except color, and the dominant force for them is the electromagnetic force.
The most stable in nature are, as a rule, neutral combinations of particles in which the charge of particles of one sign is compensated by the total charge of particles of the other sign. This corresponds to the minimum energy of the entire system. (In the same way, two bar magnets are arranged in a line, with the north pole of one facing the south pole of the other, which corresponds to the minimum energy of the magnetic field.) Gravity is an exception to this rule: negative mass does not exist. There are no bodies that fall upward.
TYPES OF MATTER
Ordinary matter is formed from electrons and quarks, grouped into objects that are neutral in color and then in electrical charge. The color power is neutralized, as will be discussed in more detail below, when the particles are combined into triplets. (Hence the term “color” itself, taken from optics: three primary colors when mixed produce white.) Thus, quarks for which the color strength is the main one form triplets. But quarks, and they are divided into u-quarks (from the English up - top) and d-quarks (from the English down - bottom), also have an electric charge equal to u-quark and for d-quark. Two u-quark and one d-quarks give an electric charge of +1 and form a proton, and one u-quark and two d-quarks give zero electric charge and form a neutron.
Stable protons and neutrons, attracted to each other by the residual color forces of interaction between their constituent quarks, form a color-neutral atomic nucleus. But nuclei carry a positive electrical charge and, attracting negative electrons that orbit around the nucleus like planets orbiting the Sun, tend to form a neutral atom. Electrons in their orbits are removed from the nucleus at distances tens of thousands of times greater than the radius of the nucleus - evidence that the electrical forces holding them are much weaker than nuclear ones. Thanks to the power of color interaction, 99.945% of an atom's mass is contained in its nucleus. Weight u- And d-quarks are about 600 times the mass of an electron. Therefore, electrons are much lighter and more mobile than nuclei. Their movement in matter is caused by electrical phenomena.
There are several hundred natural varieties of atoms (including isotopes), differing in the number of neutrons and protons in the nucleus and, accordingly, in the number of electrons in their orbits. The simplest is the hydrogen atom, consisting of a nucleus in the form of a proton and a single electron revolving around it. All “visible” matter in nature consists of atoms and partially “disassembled” atoms, which are called ions. Ions are atoms that, having lost (or gained) several electrons, have become charged particles. Matter consisting almost entirely of ions is called plasma. Stars that burn due to thermonuclear reactions occurring in the centers consist mainly of plasma, and since stars are the most common form of matter in the Universe, we can say that the entire Universe consists mainly of plasma. More precisely, stars are predominantly fully ionized hydrogen gas, i.e. a mixture of individual protons and electrons, and therefore, almost the entire visible Universe consists of it.
This is visible matter. But there is also invisible matter in the Universe. And there are particles that act as force carriers. There are antiparticles and excited states of some particles. All this leads to a clearly excessive abundance of “elementary” particles. In this abundance one can find an indication of the actual, true nature of elementary particles and the forces acting between them. According to the most recent theories, particles may be essentially extended geometric objects - “strings” in ten-dimensional space.
The invisible world.
There is not only visible matter in the Universe (but also black holes and “dark matter,” such as cold planets that become visible when illuminated). There is also truly invisible matter that permeates all of us and the entire Universe every second. It is a fast-moving gas of particles of one type - electron neutrinos.
An electron neutrino is a partner of an electron, but has no electrical charge. Neutrinos carry only a so-called weak charge. Their rest mass is, in all likelihood, zero. But they interact with the gravitational field because they have kinetic energy E, which corresponds to the effective mass m, according to Einstein's formula E = mc 2 where c– speed of light.
The key role of the neutrino is that it contributes to the transformation And-quarks in d-quarks, as a result of which a proton turns into a neutron. Neutrinos act as the "carburetor needle" for stellar fusion reactions, in which four protons (hydrogen nuclei) combine to form a helium nucleus. But since the helium nucleus does not consist of four protons, but of two protons and two neutrons, for such nuclear fusion it is necessary that two And-quarks turned into two d-quark. The intensity of the transformation determines how quickly the stars will burn. And the transformation process is determined by weak charges and weak interaction forces between particles. Wherein And-quark (electric charge +2/3, weak charge +1/2), interacting with an electron (electric charge - 1, weak charge –1/2), forms d-quark (electric charge –1/3, weak charge –1/2) and electron neutrino (electric charge 0, weak charge +1/2). The color charges (or just colors) of the two quarks cancel out in this process without the neutrino. The role of the neutrino is to carry away the uncompensated weak charge. Therefore, the rate of transformation depends on how weak the weak forces are. If they were weaker than they are, the stars would not burn at all. If they were stronger, the stars would have burned out long ago.
What about neutrinos? Because these particles interact extremely weakly with other matter, they almost immediately leave the stars in which they were born. All stars shine, emitting neutrinos, and neutrinos shine through our bodies and the entire Earth day and night. So they wander around the Universe until they enter, perhaps, into a new interaction STAR).
Carriers of interactions.
What causes forces acting between particles at a distance? Modern physics answers: due to the exchange of other particles. Imagine two speed skaters throwing a ball around. By imparting momentum to the ball when thrown and receiving momentum with the received ball, both receive a push in a direction away from each other. This can explain the emergence of repulsive forces. But in quantum mechanics, which considers phenomena in the microworld, unusual stretching and delocalization of events are allowed, which leads to the seemingly impossible: one of the skaters throws the ball in the direction from different, but that one nonetheless Maybe catch this ball. It is not difficult to imagine that if this were possible (and in the world of elementary particles it is possible), attraction would arise between the skaters.
The particles, due to the exchange of which the interaction forces between the four “particles of matter” discussed above, are called gauge particles. Each of the four interactions – strong, electromagnetic, weak and gravitational – has its own set of gauge particles. The carrier particles of the strong interaction are gluons (there are only eight of them). A photon is a carrier of electromagnetic interaction (there is only one, and we perceive photons as light). The carrier particles of the weak interaction are intermediate vector bosons (they were discovered in 1983 and 1984 W + -, W- -bosons and neutral Z-boson). The carrier particle of gravitational interaction is the still hypothetical graviton (there should be only one). All these particles, except for the photon and graviton, which can travel infinitely long distances, exist only in the process of exchange between material particles. Photons fill the Universe with light, and gravitons fill gravitational waves(not yet reliably discovered).
A particle capable of emitting gauge particles is said to be surrounded by a corresponding field of forces. Thus, electrons capable of emitting photons are surrounded by electrical and magnetic fields, as well as weak and gravitational fields. Quarks are also surrounded by all these fields, but also by the strong interaction field. Particles with a color charge in the field of color forces are affected by the color force. The same applies to other forces of nature. Therefore, we can say that the world consists of matter (material particles) and field (gauge particles). More about this below.
Antimatter.
Each particle has an antiparticle, with which the particle can mutually annihilate, i.e. "annihilate", resulting in the release of energy. “Pure” energy in itself, however, does not exist; As a result of annihilation, new particles (for example, photons) appear that carry away this energy.
In most cases, an antiparticle has properties opposite to the corresponding particle: if a particle moves to the left under the influence of strong, weak or electromagnetic fields, then its antiparticle will move to the right. In short, the antiparticle has opposite signs of all charges (except the mass charge). If a particle is composite, such as a neutron, then its antiparticle consists of components with opposite signs of charges. Thus, an antielectron has an electric charge of +1, a weak charge of +1/2 and is called a positron. Antineutron consists of And-antiquarks with electric charge –2/3 and d-antiquarks with electric charge +1/3. True neutral particles are their own antiparticles: the antiparticle of a photon is a photon.
According to modern theoretical concepts, each particle existing in nature should have its own antiparticle. And many antiparticles, including positrons and antineutrons, were indeed obtained in the laboratory. The consequences of this are extremely important and underlie all experimental particle physics. According to the theory of relativity, mass and energy are equivalent, and under certain conditions energy can be converted into mass. Since charge is conserved, and the charge of vacuum (empty space) is zero, any pairs of particles and antiparticles (with zero net charge) can emerge from the vacuum, like rabbits from a magician's hat, as long as there is enough energy to create their mass.
Generations of particles.
Accelerator experiments have shown that the quartet of material particles is repeated at least twice at higher mass values. In the second generation, the place of the electron is taken by the muon (with a mass approximately 200 times greater than the mass of the electron, but with the same values of all other charges), the place of the electron neutrino is taken by the muon (which accompanies the muon in weak interactions in the same way as the electron is accompanied by the electron neutrino), place And-quark occupies With-quark ( charmed), A d-quark – s-quark ( strange). In the third generation, the quartet consists of a tau lepton, a tau neutrino, t-quark and b-quark.
Weight t-a quark is about 500 times the mass of the lightest – d-quark. It has been experimentally established that there are only three types of light neutrinos. Thus, the fourth generation of particles either does not exist at all, or the corresponding neutrinos are very heavy. This is consistent with cosmological data, according to which no more than four types of light neutrinos can exist.
In experiments with high-energy particles, the electron, muon, tau lepton and corresponding neutrinos act as isolated particles. They do not carry a color charge and enter into only weak and electromagnetic interactions. Collectively they are called leptons.
Table 2. GENERATIONS OF FUNDAMENTAL PARTICLES | ||||
Particle | Rest mass, MeV/ With 2 | Electric charge | Color charge | Weak charge |
SECOND GENERATION | ||||
With-quark | 1500 | +2/3 | Red, green or blue | +1/2 |
s-quark | 500 | –1/3 | Same | –1/2 |
Muon neutrino | 0 | 0 | +1/2 | |
Muon | 106 | 0 | 0 | –1/2 |
THIRD GENERATION | ||||
t-quark | 30000–174000 | +2/3 | Red, green or blue | +1/2 |
b-quark | 4700 | –1/3 | Same | –1/2 |
Tau neutrino | 0 | 0 | +1/2 | |
Tau | 1777 | –1 | 0 | –1/2 |
Quarks, under the influence of color forces, combine into strongly interacting particles that dominate most high-energy physics experiments. Such particles are called hadrons. They include two subclasses: baryons(such as a proton and a neutron), which are made up of three quarks, and mesons, consisting of a quark and an antiquark. In 1947, the first meson, called the pion (or pi-meson), was discovered in cosmic rays, and for some time it was believed that the exchange of these particles - main reason nuclear forces. Omega-minus hadrons, discovered in 1964 at Brookhaven National Laboratory (USA), and the JPS particle ( J/y-meson), discovered simultaneously at Brookhaven and at the Stanford Linear Accelerator Center (also in the USA) in 1974. The existence of the omega minus particle was predicted by M. Gell-Mann in his so-called “ S.U. 3 theory" (another name is the "eight-fold path"), in which the possibility of the existence of quarks was first suggested (and this name was given to them). A decade later, the discovery of the particle J/y confirmed the existence With-quark and finally made everyone believe in both the quark model and the theory that united electromagnetic and weak forces ( see below).
Particles of the second and third generation are no less real than the first. True, having arisen, in millionths or billionths of a second they decay into ordinary particles of the first generation: electron, electron neutrino, and also And- And d-quarks. The question of why there are several generations of particles in nature still remains a mystery.
Different generations of quarks and leptons are often spoken of (which, of course, is somewhat eccentric) as different “flavors” of particles. The need to explain them is called the “flavor” problem.
BOSONS AND FERMIONS, FIELD AND MATTER
One of the fundamental differences between particles is the difference between bosons and fermions. All particles are divided into these two main classes. Identical bosons can overlap or overlap, but identical fermions cannot. Superposition occurs (or does not occur) in the discrete energy states into which quantum mechanics divides nature. These states are like separate cells into which particles can be placed. So, you can put as many identical bosons as you like into one cell, but only one fermion.
As an example, consider such cells, or “states,” for an electron orbiting the nucleus of an atom. Unlike planets solar system, the electron, according to the laws of quantum mechanics, cannot circulate in any elliptical orbit; for it there is only a discrete series of allowed “states of motion.” Sets of such states, grouped according to the distance from the electron to the nucleus, are called orbitals. In the first orbital there are two states with different angular momentum and, therefore, two allowed cells, and in higher orbitals there are eight or more cells.
Since the electron is a fermion, each cell can only contain one electron. Very important consequences follow from this - all of chemistry, since the chemical properties of substances are determined by the interactions between the corresponding atoms. If you go through the periodic system of elements from one atom to another in the order of increasing by one the number of protons in the nucleus (the number of electrons will also increase accordingly), then the first two electrons will occupy the first orbital, the next eight will be located in the second, etc. This consistent change in the electronic structure of atoms from element to element determines the patterns in their chemical properties.
If electrons were bosons, then all the electrons in an atom could occupy the same orbital, corresponding to the minimum energy. In this case, the properties of all matter in the Universe would be completely different, and the Universe in the form in which we know it would be impossible.
All leptons - electron, muon, tau lepton and their corresponding neutrinos - are fermions. The same can be said about quarks. Thus, all particles that form “matter”, the main filler of the Universe, as well as invisible neutrinos, are fermions. This is quite significant: fermions cannot combine, so the same applies to objects in the material world.
At the same time, all the “gauge particles” that are exchanged between interacting material particles and which create a field of forces ( see above), are bosons, which is also very important. So, for example, many photons can be in the same state, forming a magnetic field around a magnet or an electric field around an electric charge. Thanks to this, laser is also possible.
Spin.
The difference between bosons and fermions is associated with another characteristic of elementary particles - spin. Surprisingly, all fundamental particles have their own angular momentum or, more simply put, rotate around their own axis. Momentum - characteristic rotational movement, as well as the total impulse – translational. In any interaction, angular momentum and momentum are conserved.
In the microcosm, the angular momentum is quantized, i.e. takes discrete values. In suitable units of measurement, leptons and quarks have a spin of 1/2, and gauge particles have a spin of 1 (except for the graviton, which has not yet been observed experimentally, but theoretically should have a spin of 2). Since leptons and quarks are fermions, and gauge particles are bosons, we can assume that “fermionicity” is associated with spin 1/2, and “bosonicity” is associated with spin 1 (or 2). Indeed, both experiment and theory confirm that if a particle has a half-integer spin, then it is a fermion, and if it has an integer spin, then it is a boson.
GAUGE THEORIES AND GEOMETRY
In all cases, the forces arise due to the exchange of bosons between fermions. Thus, the color force of interaction between two quarks (quarks - fermions) arises due to the exchange of gluons. A similar exchange occurs constantly in protons, neutrons and atomic nuclei. Similarly, the photons exchanged between electrons and quarks create the electrical attractive forces that hold electrons in the atom, and the intermediate vector bosons exchanged between leptons and quarks create the weak forces responsible for converting protons into neutrons in thermonuclear reactions in stars.
The theory behind this exchange is elegant, simple, and probably correct. It is called gauge theory. But at present there are only independent gauge theories of strong, weak and electromagnetic interactions and a similar, although somewhat different, gauge theory of gravity. One of the most important physical problems is the reduction of these individual theories into a single and at the same time simple theory, in which they would all become different aspects of a single reality - like the faces of a crystal.
Table 3. SOME HADRONS | ||||
Particle | Symbol | Quark composition * | Rest mass, MeV/ With 2 | Electric charge |
BARIONS | ||||
Proton | p | uud | 938 | +1 |
Neutron | n | udd | 940 | 0 |
Omega minus | W – | sss | 1672 | –1 |
MESONS | ||||
Pi-plus | p + | u | 140 | +1 |
Pi minus | p – | du | 140 | –1 |
Fi | f | sє | 1020 | 0 |
JP | J/y | cў | 3100 | 0 |
Upsilon | Ў | b | 9460 | 0 |
* Quark composition: u– top; d– lower; s- strange; c– enchanted; b- Beautiful. Antiques are indicated by a line above the letter. |
The simplest and oldest of the gauge theories is the gauge theory of electromagnetic interaction. In it, the charge of an electron is compared (calibrated) with the charge of another electron distant from it. How can you compare charges? You can, for example, bring the second electron closer to the first and compare their interaction forces. But doesn't the charge of an electron change when it moves to another point in space? The only way to check is to send a signal from a near electron to a far one and see how it reacts. The signal is a gauge particle – a photon. To be able to test the charge on distant particles, a photon is needed.
Mathematically, this theory is extremely accurate and beautiful. From the “gauge principle” described above flows all of quantum electrodynamics (quantum theory of electromagnetism), as well as Maxwell’s theory of the electromagnetic field - one of the greatest scientific achievements 19th century
Why is such a simple principle so fruitful? Apparently, it expresses a certain correlation between different parts of the Universe, allowing measurements to be made in the Universe. In mathematical terms, the field is interpreted geometrically as the curvature of some conceivable “internal” space. Measuring charge is measuring the total “internal curvature” around the particle. The gauge theories of the strong and weak interactions differ from the electromagnetic gauge theory only in the internal geometric “structure” of the corresponding charge. The question of where exactly this internal space is is sought to be answered by multidimensional unified field theories, which are not discussed here.
Table 4. FUNDAMENTAL INTERACTIONS | |||||
Interaction | Relative intensity at a distance of 10–13 cm | Radius of action | Interaction carrier | Carrier rest mass, MeV/ With 2 | Spin the carrier |
Strong | 1 | Gluon | 0 | 1 | |
Electro- magnetic |
0,01 | Ґ | Photon | 0 | 1 |
Weak | 10 –13 | W + | 80400 | 1 | |
W – | 80400 | 1 | |||
Z 0 | 91190 | 1 | |||
Gravita- tional |
10 –38 | Ґ | Graviton | 0 | 2 |
Particle physics is not yet complete. It is still far from clear whether the available data is sufficient to fully understand the nature of particles and forces, as well as the true nature and dimension of space and time. Do we need experiments with energies of 10 15 GeV for this, or will the effort of thought be sufficient? No answer yet. But we can say with confidence that the final picture will be simple, elegant and beautiful. It is possible that there will not be so many fundamental ideas: the gauge principle, spaces of higher dimensions, collapse and expansion, and, above all, geometry.
Microworld structures
Previously, elementary particles were called particles that are part of an atom and cannot be broken down into more elementary components, namely electrons and nuclei.
Later it was found that nuclei consist of simpler particles - nucleons(protons and neutrons), which in turn consist of other particles. That's why the smallest particles of matter began to be considered elementary particles , excluding atoms and their nuclei .
To date, hundreds of elementary particles have been discovered, which requires their classification:
– by type of interaction
- by time of life
– largest back
Elementary particles are divided into the following groups:
Composite and fundamental (structureless) particles
Compound particles
Hadrons (heavy)– particles participating in all types of fundamental interactions. They consist of quarks and are divided, in turn, into: mesons– hadrons with integer spin, that is, they are bosons; baryons– 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, i.e. nucleons.
Fundamental (structureless) particles
Leptons (light)– fermions, which have the form of point particles (i.e., 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.
Quarks– fractionally charged particles that make up hadrons. They were not observed in the free state.
Gauge bosons– particles through the exchange of which interactions are carried out:
– photon – a particle that carries electromagnetic interaction;
– eight gluons – particles that carry the strong interaction;
– three intermediate vector bosons W + , W− and Z 0, which tolerate weak interactions;
– graviton is a hypothetical particle that transfers gravitational interaction. 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.
By modern ideas, fundamental particles (or “true” elementary particles) that do not have an internal structure and finite dimensions include:
Quarks and leptons
Particles that provide fundamental interactions: gravitons, photons, vector bosons, gluons.
Classification of elementary particles by lifetime:
- stable: particles whose lifetime is very long (in the limit it tends to infinity). These include electrons , protons , neutrino . Neutrons are also stable inside nuclei, but they are unstable outside the nucleus.
- unstable (quasi-stable): elementary particles are those particles that decay due to electromagnetic and weak interactions, and whose lifetime is more than 10–20 seconds. Such particles include free neutron (i.e. a neutron outside the nucleus of an atom)
- resonances (unstable, short-lived). Resonances include elementary particles that decay due to strong interactions. Their lifetime is less than 10 -20 seconds.
Classification of particles by participation in interactions:
- leptons : These include neutrons. All of them do not participate in the whirlpool of intranuclear interactions, i.e. are not subject to strong interactions. They participate in weak interaction, and those with an electric charge also participate in electromagnetic interaction
- hadrons : particles that exist inside the atomic nucleus and participate in strong interactions. The most famous of them are proton And neutron .
Known today six leptons :
In the same family as the electron are muons and tau particles, which are similar to the electron but more massive. Muons and tau particles are unstable and eventually decay into several other particles, including the electron
Three electrically neutral particles with zero (or close to zero, scientists have not yet decided on this point) mass, called neutrino . Each of the three neutrinos (electron neutrino, muon neutrino, tau neutrino) is paired with one of three types of particles of the electron family.
The most famous hadrons , protons and neutrinos there are hundreds of relatives, which are born in large numbers and immediately decay in the process of various nuclear reactions. With the exception of the proton, they are all unstable and can be classified according to the composition of the particles into which they decay:
If there is a proton among the final products of particle decay, then it is called baryon
If there is no proton among the decay products, then the particle is called meson .
The chaotic picture of the subatomic world, which became more complex with the discovery of each new hadron, gave way to a new picture with the advent of the concept of quarks. According to the quark model, all hadrons (but not leptons) consist of even more elementary particles - quarks. So baryons (in particular the proton) consist of three quarks, and mesons - from the pair quark - antiquark.
Generation | Quarks with charge (+2/3) | Quarks with charge (−1/3) | ||||||
Quark/antiquark symbol | Mass (MeV) | Name/flavor of quark/antiquark | Quark/antiquark symbol | Mass (MeV) | ||||
---|---|---|---|---|---|---|---|---|
1 | u-quark (up-quark) / anti-u-quark | texvc not found; See math/README for setup help.): u / \, \overline(u)
|
from 1.5 to 3 | d-quark (down-quark) / anti-d-quark | Unable to parse expression (Executable file texvc not found; See math/README for setup help.): d / \, \overline(d)
|
4.79±0.07 | ||
2 | c-quark (charm-quark) / anti-c-quark | Unable to parse expression (Executable file texvc not found; See math/README for setup help.): c / \, \overline(c)
|
1250 ± 90 | s-quark (strange quark) / anti-s-quark | Unable to parse expression (Executable file texvc not found; See math/README for setup help.): s / \, \overline(s)
|
95 ± 25 | ||
3 | t-quark (top-quark) / anti-t-quark | Unable to parse expression (Executable file texvc not found; See math/README for setup help.): t / \, \overline(t)
|
174 200 ± 3300 | b-quark (bottom-quark) / anti-b-quark | Unable to parse expression (Executable file texvc not found; See math/README for setup help.): b / \, \overline(b)
|
4200±70 |
see also
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Notes
Links
- S. A. Slavatinsky// Moscow Institute of Physics and Technology (Dolgoprudny, Moscow region)
- Slavatinsky S.A. // SOZH, 2001, No. 2, p. 62–68 archive http://web.archive.org/web/20060116134302/http://journal.issep.rssi.ru/annot.php?id=S1176
- // nuclphys.sinp.msu.ru
- // second-physics.ru
- //physics.ru
- // nature.web.ru
- // nature.web.ru
- // nature.web.ru
The most famous formula from general relativity is the law of conservation of energy-mass | This is a draft article on physics. You can help the project by adding to it. |
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Units physical quantities when describing phenomena occurring in the microworld, they are divided into basic and derivative, which are determined through the mathematical notation of the laws of physics.
Due to the fact that all physical phenomena occur in space and time, the basic units are primarily taken to be the units of length and time, followed by the unit of mass. Basic units: lengths l, time t, mass m - receive a certain dimension. The dimensions of derived units are determined by formulas expressing certain physical laws.
The sizes of the main physical units are selected so that in practice it is convenient to use them.
The following dimensions are accepted in the SI system: lengths [ l] = m (meter), time [t] = s (second), mass [t] = kg (kilogram).
In the CGS system, the following dimensions are accepted for basic units: length [/] = cm (centimeter), time [t] = s (second) and mass [t] = g (gram). To describe phenomena occurring in the microcosm, both SI and CGS units can be used.
Let us estimate the orders of magnitude of length, time and mass in the phenomena of the microworld.
In addition to the generally accepted international systems of units SI and GHS, “natural systems of units” are also used, based on universal physical constants. These systems of units are particularly relevant and are used in various physical theories. In the natural system of units, fundamental constants are taken as the basic units: the speed of light in vacuum − c, Planck’s constant − ћ, gravitational constant G N, Boltzmann’s constant − k: Avogadro’s number − N A, etc. In the natural system of Planck units it is accepted c = ћ = G N = k = 1. This system of units is used in cosmology to describe processes in which quantum and gravitational effects are simultaneously significant (theories of Black holes, theories of the early Universe).
In the natural system of units, the problem of the natural unit of length is solved. This can be considered the Compton wavelength λ 0, which is determined by the mass of the particle M: λ 0 = ћ/Мс.
Length characterizes the size of the object. So, for an electron, the classical radius is r 0 = e 2 /m e c 2 = 2.81794·10 -13 cm (e, m e - charge and mass of the electron). The classical radius of an electron has the meaning of the radius of a charged ball with charge e (the distribution is spherically symmetric), at which the energy of the electrostatic field of the ball ε = γе 2 /r 0 is equal to the rest energy of the electron m e c 2 (used when considering Thompson scattering of light).
The radius of the Bohr orbit is also used. It is defined as the distance from the nucleus at which an electron is most likely to be found in an unexcited hydrogen atom
a 0 = ћ 2 /m e e 2 (in the SGS system) and a 0 = (α/4π)R = 0.529·10 -10 m (in the SI system), α = 1/137.
Nucleon size r ≈ 10 -13 cm (1 femtometer). The characteristic dimensions of atomic systems are 10 -8, nuclear systems are 10 -12 ÷ 10 -13 cm.
Time varies over a wide range and is defined as the ratio of the distance R to the speed of the object v. For microobjects τ poison = R/v = 5·10 -12 cm/10 9 cm/s ~ 5·10 -22 s;
τ element h = 10 -13 cm/3·10 10 cm/s = 3·10 -24 s.
Masses objects change from 0 to M. Thus, the mass of an electron m e ≈ 10 -27 g, the mass of a proton
m р ≈ 10 -24 g (SGS system). One atomic mass unit used in atomic and nuclear physics, 1 amu. = M(C)/12 in units of carbon atom mass.
The fundamental characteristics of micro-objects include electric charge, as well as the characteristics necessary to identify an elementary particle.
Electric charge
particles Q is usually measured in units of electron charge. Electron charge e = 1.6·10 -19 coulombs. For particles in a free state, Q/e = ±1.0, and for quarks that are part of hadrons, Q/e = ±2/3 and ±1/3.
In nuclei, charge is determined by the number of protons Z contained in the nucleus. Proton charge by absolute value equal to the charge of the electron.
To identify an elementary particle you need to know:
I – isotopic spin;
J – intrinsic angular momentum – spin;
P – spatial parity;
C – charge parity;
G − G-parity.
This information is written in the form of the formula I G (J PC).
Spin− one of the most important characteristics of a particle, for which the fundamental Planck constant h or ћ = h/2π = 1.0544·10 -27 [erg-s] is used. Bosons have an integer spin in units ћ: (0,1, 2,...)ћ, fermions have a half-integer spin (1/2, 3/2,.. .)ћ. In the class of supersymmetric particles, the spin values of fermions and bosons are reversed.
Rice. Figure 4 illustrates the physical meaning of spin J by analogy with the classical concept of angular momentum of a particle with mass m = 1 g moving at a speed v = 1 cm/s in a circle with radius r = 1 cm. In classical physics, angular momentum J = mvr = L (L is orbital momentum). In quantum mechanics, J = = 10 27 ћ = 1 erg·s for the same parameters of an object moving in a circle, where ћ = 1.05·10 -27 erg·s.
The projection of the spin of an elementary particle onto the direction of its momentum is called helicity. The helicity of a massless particle with an arbitrary spin takes only two values: along or against the direction of the particle's momentum. For a photon, the possible values of helicity are equal to ±1, for a massless neutrino, the helicity is equal to ±1/2.
The spin angular momentum of an atomic nucleus is defined as the vector sum of the spins of the elementary particles forming a quantum system and the orbital angular moments of these particles due to their motion within the system. Orbital momentum ||, and spin momentum || acquire discrete meaning. Orbital momentum || = ћ[ l(l+1)] 1/2 , where l− orbital quantum number (can take values 0, 1,2,...), intrinsic angular momentum || = ћ 1/2 where s is the spin quantum number (can take zero, integer or half-integer values J, the total angular momentum is equal to the sum + = .
Derived units include: particle energy, speed, replacing speed for relativistic particles, magnetic moment, etc.
Energy particle at rest: E = mc 2 ; moving particle: E = m 2 c 4 + p 2 c 2.
For non-relativistic particles: E = mc 2 + p 2 /2m; for relativistic particles, with mass m = 0: E = avg.
Energy units - eV, keV, MeV, GeV, TeV, ... 1 GeV = 10 9 eV, 1 TeV = 10 12 eV,
1 eV = 1.6·10 -12 erg.
Particle speed
β = v/c, where c = 3·10 10 cm/s is the speed of light. The particle speed determines such an important characteristic as the Lorentz factor of the particle γ = 1/(1-β 2) 1/2 = E/mc 2. Always γ > 1- For non-relativistic particles 1< γ < 2, а для релятивистских частиц γ > 2.
In high-energy physics, the velocity of a particle β is close to 1 and is difficult to determine for relativistic particles. Therefore, instead of speed, speed y is used, which is related to speed by the relation y = (1/2)ln[(1+β)/(1-β)] = (1/2)ln[(E+p)/(E-p) ]. The speed varies from 0 to ∞.
The functional relationship between particle velocity and rapidity is shown in Fig. 5. For relativistic particles at β → 1, E → p, then instead of rapidity we can use pseudo-rapidity η, which is determined by the particle departure angle θ, η = (1/2)ln tan(θ/2). Unlike speed, speed is an additive quantity, i.e. y 2 = y 0 + y 1 for any frame of reference and for any relativistic and non-relativistic particles.
Magnetic moment
μ = Iπr 2 /c, where the current I = ev/2πr arises due to the rotation of the electric charge. Thus, any charged particle has a magnetic moment. When considering the magnetic moment of an electron, the Bohr magneton is used
μ B = eћ/2m e c = 0.5788·10 -14 MeV/G, electron magnetic moment = g·μ B ·. The coefficient g is called the gyromagnetic ratio. For an electron g = /μ B · = 2, because J = ћ/2, = μ B provided that the electron is a point-like structureless particle. The gyromagnetic ratio g contains information about the structure of the particle. The quantity (g − 2) is measured in experiments aimed at studying the structure of particles other than leptons. For leptons, this value indicates the role of higher electromagnetic corrections (see further section 7.1).
In nuclear physics, the nuclear magneton is used μ i = eћ/2m p c, where m p is the proton mass.
2.1.1. The Heaviside system and its connection with the GHS system
In the Heaviside system, the speed of light c and Planck’s constant ћ are assumed to be equal to unity, i.e. с = ћ = 1. The main units of measurement are energy units − MeV or MeV -1, while in the GHS system the main units of measurement are [g, cm, s]. Then, using the relations: E = mc 2 = m = MeV, l= ћ/mc = MeV -1, t = ћ/mc 2 = MeV -1, we obtain the connection between the Heaviside system and the SGS system in the form:- m(g) = m(MeV) 2 10 -27,
- l(cm) = l(MeV -1) 2 10 -11 ,
- t (s) = t (MeV -1) b.b 10 -22.
The Heaviside system is used in high-energy physics to describe phenomena occurring in the microcosm, and is based on the use of natural constants c and ћ, which are decisive in relativistic and quantum mechanics.
The numerical values of the corresponding quantities in the CGS system for the electron and proton are given in Table. 3 and can be used to move from one system to another.
Table 3. Numerical values of quantities in the CGS system for electron and proton
2.1.2. Planck (natural) units
When considering gravitational effects, the Planck scale is introduced to measure energy, mass, length and time. If the gravitational energy of an object is equal to its total energy, i.e.
That
length = 1.6·10 -33 cm,
mass = 2.2·10 -5 g = 1.2·10 19 GeV,
time = 5.4·10 -44 s,
Where = 6.67·10 -8 cm 2 ·g -1 ·s -2 .
Gravitational effects are significant when the gravitational energy of an object is comparable to its total energy.
2.2. Classification of elementary particles
The concept of “elementary particle” was formed with the establishment of the discrete nature of the structure of matter at the microscopic level.
Atoms → nuclei → nucleons → partons (quarks and gluons)
In modern physics, the term “elementary particles” is used to name a large group of tiny observed particles of matter. This group of particles is very extensive: p protons, n neutrons, π- and K-mesons, hyperons, charmed particles (J/ψ...) and many resonances (in total
~ 350 particles). These particles are called "hadrons".
It turned out that these particles are not elementary, but represent composite systems, the constituents of which are truly elementary or, as they came to be called, " fundamental
" particles − partons, discovered while studying the structure of the proton. The study of the properties of partons made it possible to identify them with quarks And gluons, introduced into consideration by Gell-Mann and Zweig when classifying observable elementary particles. The quarks turned out to be fermions with spin J = 1/2. They were assigned fractional electric charges and a baryon number B = 1/3, since a baryon with B = 1 consists of three quarks. In addition, to explain the properties of some baryons, it became necessary to introduce a new quantum number—color. Each quark has three color states, denoted by the indices 1, 2, 3 or the words red (R), green (G) and blue (B). Color does not manifest itself in any way in observed hadrons and only works inside them.
To date, 6 flavors (types) of quarks have been discovered.
In table 4 shows the properties of quarks for one color state.
Table 4. Properties of quarks
Aroma | Mass, MeV/s 2 | I | I 3 | Q q /e | s | With | b | t |
u up | 330; (5) | 1/2 | 1/2 | 2/3 | 0 | 0 | 0 | 0 |
d down | 340; (7) | 1/2 | -1/2 | -1/3 | 0 | 0 | 0 | 0 |
s strange | 450; (150) | 0 | 0 | -1/3 | -1 | 0 | 0 | 0 |
with charm | 1500 | 0 | 0 | 2/3 | 0 | 1 | 0 | 0 |
b beauty | 5000 | 0 | 0 | -1/3 | 0 | 0 | -1 | 0 |
t truth | 174000 | 0 | 0 | 2/3 | 0 | 0 | 0 | 1 |
For each flavor of a quark, its mass is indicated (the masses of constituent quarks and the masses of current quarks are given in parentheses), the isotopic spin I and the 3rd projection of the isotopic spin I 3 , the quark charge Q q /e and the quantum numbers s, c, b, t. Along with these quantum numbers, the quantum number hypercharge Y = B + s + c + b+ t is often used. There is a connection between the projection of isotopic spin I 3 , electric charge Q and hypercharge Y: Q = I 3 + (1/2)Y.
Since each quark has 3 colors, 18 quarks must be considered. Quarks have no structure.
At the same time, among the elementary particles there was a whole class of particles called " leptons"They are also fundamental particles, i.e. they have no structure. There are six of them: three charged e, μ, τ and three neutral ones ν e, ν μ, ν τ. Leptons participate only in electromagnetic and weak interactions. Leptons and quarks with half-integer spin J = (n+1/2)ћ, n = 0, 1,... belong to the fundamental fermions.A surprising symmetry is observed between leptons and quarks: six leptons and six quarks.
In table Figure 5 shows the properties of fundamental fermions: electric charge Q i in units of electron charge and particle mass m. Leptons and quarks are combined into three generations (I, II and III). For each generation, the sum of electric charges ∑Q i = 0, taking into account 3 color charges for each quark. Each fermion has a corresponding antifermion.
In addition to the characteristics of the particles indicated in the table, an important role for leptons is played by lepton numbers: electron L e, equal to +1 for e - and ν e, muonic L μ, equal to +1 for μ - and ν μ and taonic L τ, equal to + 1 for τ - and ν τ, which correspond to the flavors of leptons involved in specific reactions and are conserved quantities. For leptons, the baryon number B = 0.
Table 5. Properties of fundamental fermions
The matter around us consists of first-generation fermions of non-zero mass. The influence of particles of the second and third generations manifested itself in the early Universe. Among fundamental particles, a special role is played by fundamental gauge bosons, which have an integer internal quantum number of spin J = nћ, n = 0, 1, .... Gauge bosons are responsible for four types of fundamental interactions: strong (gluon g), electromagnetic (photon γ) , weak (bosons W ± , Z 0), gravitational (graviton G). They are also structureless, fundamental particles.
In table 6 shows the properties of fundamental bosons, which are field quanta in gauge theories.
Table 6. Properties of fundamental bosons
Name | Charge | Weight | Spin | Interactions |
Graviton, G | 0 | 0 | 2 | Gravitational |
Photon, γ | 0 | < 3·10 -27 эВ | 1 | Electromagnetic |
Charged vector bosons, W ± | ±1 | 80.419 GeV/s 2 | 1 | Weak |
Neutral vector boson, Z 0 | 0 | 91.188 GeV/s 2 | 1 | Weak |
Gluons, g 1 , ... , g 8 | 0 | 0 | 0 | Strong |
Higgs, H 0 , H ± | 0 | > 100 GeV/s 2 | 0 |
In addition to the properties of the open gauge bosons γ, W ±, Z 0, g 1,..., g 8, the table shows the properties of so far undiscovered bosons: the graviton G and the Higgs bosons H 0, H ±.
Let us now consider the most numerous group of elementary strongly interacting particles - hadrons, to explain the structure of which the concept of quarks was introduced.
Hadrons are divided into mesons and baryons. Mesons are built from a quark and an antiquark (q). Baryons consist of three quarks (q 1 q 2 q 3).
In table 7 provides a list of properties of the main hadrons. (For detailed tables, see The European Physical Journal C, Rev. of Particle Phys., v.15, No. 1 - 4, 2000.)
Table 7. Properties of hadrons
Name | Mass, MeV/s 2 | Life time, s | Decay modes | Quark composition | |||||||||||
Peony π ± 1 - (0 -+) π 0 |
139.567 134.965 |
2.6·10 -8 |
π ± → μ ± + ν π 0 → γ + γ |
(u), (d) (u − d)/√2 |
|||||||||||
η-meson η 0 0 + (0 -+) |
548.8 | Г=1.18±0.11 keV | η 0 → γ + γ; 3π 0 →π + + π -0 + π -- |
c 1 (u + d) + c 2 (s) | |||||||||||
|
|||||||||||||||
D ± D0 |
1869.3 1864.5 |
10.69·10 -13 4.28·10 -13 |
D ± → e ± + X |
(c), (d) (c) |
|||||||||||
F ± = | 1969.3 | 4.36·10 -13 | → ρ 0 + π ± | (c, s) | |||||||||||
B ± B 0 |
5277.6 5279.4 | 13.1·10 -13 13.1·10 -13 |
B ± → + π ± B 0 →+ π -0 + |
(u), (b) (d), (b) |
|||||||||||
b | Proton p Neutron n |
938.3 939.5 |
> 10 33 years 898 ±16 |
n → р + e - + |
uud udd |
||||||||||
Λ | 2.63·10 -10 | Λ→p + π - | uds | ||||||||||||
Σ + Σ 0 Σ - |
1189.4 1192 1197 |
0.8·10 -10 5.8·10 -20 1.48·10 -10 |
Σ + →p + π 0 Σ 0 → Λ+ γ Σ - →n + π - |
uus uds dds |
|||||||||||
Ξ 0 Ξ - |
1314.9 1321 |
2.9·10 -10 1.64·10 -10 |
Ξ 0 → Λ+ π 0 Ξ - → Λ + π - |
uss dss |
|||||||||||
Ω - | 1672 | 0.8·10 -10 | Ω - → Λ+ K - | sss | |||||||||||
|
|
|
The quark structure of hadrons makes it possible to distinguish in this large group of particles non-strange hadrons, which consist of non-strange quarks (u, d), strange hadrons, which include a strange quark s, charmed hadrons containing a c-quark, pretty hadrons (bottom hadrons) with b-quark.
The table shows the properties of only a small part of hadrons: mesons and baryons. Their mass, lifetime, main decay modes and quark composition are shown. For mesons, the baryon number B = O and the lepton number L = 0. For baryons, the baryon number B = 1, the lepton number L = 0. Mesons are bosons (integer spin), baryons are fermions (half-integer spin).
Further consideration of the properties of hadrons allows us to combine them into isotopic multiplets, consisting of particles with the same quantum numbers (baryon number, spin, internal parity, strangeness) and similar masses, but with different electric charges. Each isotopic multiplet is characterized by isotopic spin I, which determines the total number of particles included in the multiplet, equal to 2I + 1. Isospin can take values 0, 1/2, 1, 3/2, 2, . .., i.e. the existence of isotopic singlets, doublets, triplets, quartets, etc. is possible. Thus, a proton and a neutron constitute an isotopic doublet, π + -, π - -, π 0 -mesons are considered as an isotopic triplet.
More complex objects in the microcosm are atomic nuclei. The atomic nucleus consists of Z protons and N neutrons. The sum Z + N = A is the number of nucleons in a given isotope. Often the tables give the value averaged over all isotopes, then it becomes fractional. Nuclei are known for which the indicated values are within the limits: 1< А < 289, 1 < Z < 116.
The particles listed above are considered within the framework of the Standard Model. It is assumed that beyond the Standard Model there may exist another group of fundamental particles - supersymmetric particles (SUSY). They must ensure symmetry between fermions and bosons. In table 8 shows the expected properties of this symmetry.
2.3. Field approach to the problem of interactions
2.3.1 Properties of fundamental interactions
The huge variety of physical phenomena that occur during collisions of elementary particles is determined by only four types of interactions: electromagnetic, weak, strong and gravitational. In quantum theory, interaction is described in terms of the exchange of specific quanta (bosons) associated with a given type of interaction.
To visually represent the interaction of particles, the American physicist R. Feynman proposed the use of diagrams, which received his name. Feynman diagrams describe any interaction process when two particles collide. Each particle involved in the process is represented by a line on the Feynman diagram. The free left or right end of the line indicates that the particle is in the initial or final state, respectively. The internal lines in the diagrams (i.e. lines that do not have free ends) correspond to the so-called virtual particles. These are particles created and absorbed during the interaction process. They cannot be registered, unlike real particles. The interaction of particles in the diagram is represented by nodes (or vertices). The type of interaction is characterized by the coupling constant α, which can be written as: α = g 2 /ћc, where g is the charge of the interaction source, and is the main quantitative characteristic of the force acting between particles. In electromagnetic interaction α e = e 2 /ћc = 1/137.
![]() Fig.6. Feynman diagram. |
The process a + b →с + d in the form of a Feynman diagram (Fig. 6) looks like this: R is a virtual particle exchanged between particles a and b during interaction determined by the interaction constant α = g 2 /ћc, characterizing the strength of interaction at a distance , equal to the interaction radius.
A virtual particle can have a mass M x and when this particle is exchanged, a 4-momentum t = −q 2 = Q 2 is transferred.
In table 9 shows the characteristics different types interactions.
Electromagnetic interactions
. Electromagnetic interactions, to which all charged particles and photons are subject, have been studied most fully and consistently. The carrier of interaction is the photon. For electromagnetic forces, the interaction constant is numerically equal to the fine structure constant α e = e 2 /ћc = 1/137.
Examples of the simplest electromagnetic processes are the photoelectric effect, the Compton effect, the formation of electron-positron pairs, and for charged particles - ionization scattering and bremsstrahlung. The theory of these interactions - quantum electrodynamics - is the most accurate physical theory.
Weak interactions.
For the first time, weak interactions were observed during the beta 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:
p → n + e + + ν e, n → p + e - + e. Reverse reactions are also possible: capture of an electron e - + p → n + ν e or an antineutrino e + p → e + + n. The weak interaction was described by Enrico Fermi in 1934 in terms of the four-fermion contact interaction defined by the Fermi constant
G F = 1.4·10 -49 erg·cm 3 .
At very high energies, instead of the Fermi contact interaction, the weak interaction is described as an exchange interaction, in which a quantum endowed with a weak charge g w (by analogy with an electric charge) is exchanged and acts between fermions. Such quanta were first discovered in 1983 at the SppS collider (CERN) by a team led by Carl Rubbia. These are charged bosons - W ± and a neutral boson - Z 0, their masses are respectively equal: m W± = 80 GeV/s 2 and m Z = 90 GeV/s 2. The interaction constant α W in this case is expressed through the Fermi constant:
Table 9. Main types of interactions and their characteristics
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