About the understanding of the movement of matter, its ability to self-development, as well as the connection and interaction of material objects in modern natural science. Fundamental particles How the “not” particle works
Leptons do not participate in the strong interaction. electron. positron. muon. neutrino is a light neutral particle that participates only in weak and gravitational interaction. neutrino (# flux). quarks. carriers of interactions: photon quantum of light...
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The request "Elementary particles" is redirected here; see also other meanings. Elementary particle is a collective term referring to micro-objects on a subnuclear scale that cannot be broken down into their component parts. Should have in... ... Wikipedia
Elementary particle is a collective term referring to micro-objects on a subnuclear scale that cannot (or have not yet been proven to be) split into their component parts. Their structure and behavior are studied by particle physics. Concept... ...Wikipedia
electron- ▲ fundamental particle having, element, charge electron negatively charged elementary particle with elementary electric charge. ↓ … Ideographic Dictionary of the Russian Language
Elementary particle is a collective term referring to micro-objects on a subnuclear scale that cannot (or have not yet been proven to be) split into their component parts. Their structure and behavior are studied by particle physics. Concept... ...Wikipedia
This term has other meanings, see Neutrino (meanings). electron neutrino muon neutrino tau neutrino Symbol: νe νμ ντ Composition: Elementary particle Family: Fermions ... Wikipedia
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
One of the most ambiguous philosophies. concepts to which one (or some) of the following meanings is given: 1) something whose defining characteristics are extension, location in space, mass, weight, movement, inertia, resistance,... ... Philosophical Encyclopedia
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- Kinetic theory of gravity and foundations of a unified theory of matter, V. Ya. Bril. All material objects of Nature (both material and field) are discrete. They consist of elementary string-shaped particles. An undeformed fundamental string is a field particle...
Interesting article
Recently, physicists observing another experiment taking place at the Large Hadron Collider finally managed to find traces of the Higgs boson, or, as many journalists call it, the “god particle.” This means that the construction of the collider was completely justified - after all, it was made precisely in order to catch this elusive boson.
Physicists working at the Large Hadron Collider using the CMS detector have for the first time detected the birth of two Z bosons - one of the types of events that may be evidence of the existence of a “heavy” version of the Higgs boson. To be precise, on October 10, the CMS detector detected the appearance of four muons for the first time. Preliminary reconstruction results allowed scientists to interpret this event as a candidate for the production of two neutral gauge Z bosons.
I think now we should digress a little and talk about what these muons, bosons and other elementary particles are. According to the standard model of quantum mechanics, the entire world consists of various elementary particles, which, when in contact with each other, generate all known types of mass and energy.
All matter, for example, consists of 12 fundamental fermion particles: 6 leptons, such as the electron, muon, tau lepton, and three types of neutrinos and 6 quarks (u, d, s, c, b, t), which can be combined three generations of fermions. Fermions are particles that can be in a free state, but quarks are not; they are part of other particles, for example, well-known protons and neutrons.
Moreover, each of the particles participates in a certain type of interaction, of which, as we remember, there are only four: electromagnetic, weak (the interaction of particles during the β-decay of the atomic nucleus), strong (it seems to hold the atomic nucleus together) and gravitational. The latter, the result of which is, for example, gravity, is not considered by the standard model, since the graviton (the particle that provides it) has not yet been found.
With other types, everything is simpler - physicists know the particles that participate in them by sight. For example, quarks participate in strong, weak and electromagnetic interactions; charged leptons (electron, muon, tau-lepton) - in weak and electromagnetic ones; neutrinos - only in weak interactions.
However, in addition to these “mass” particles, there are also so-called virtual particles, some of which (for example, a photon) have no mass at all. To be honest, virtual particles are more of a mathematical phenomenon than a physical reality, since no one has ever “seen” them before. However, in various experiments, physicists can notice traces of their existence, since, alas, it is very short-lived.
What are these interesting particles? They are born only at the moment of some interaction (from those described above), after which they either decay or are absorbed by one of the fundamental particles. It is believed that they, as it were, “transfer” the interaction, that is, by contacting fundamental particles, they change their characteristics, due to which the interaction, in fact, occurs.
So, for example, in electromagnetic interactions, which are best studied, electrons constantly absorb and emit virtual massless particles photons, as a result of which the properties of the electrons themselves are slightly changed and they become capable of such feats as, for example, directed movement (i.e. electric current ), or a “jump” to another energy level (as happens during photosynthesis in plants). Virtual particles also work in other types of interactions.
In addition to the photon, modern physics also knows two more types of virtual particles, called bosons and gluons. Bosons are especially interesting for us now - it is believed that in all interactions, fundamental particles constantly exchange them and thereby influence each other. The bosons themselves are considered massless particles, although some experiments show that this is not entirely true - W- and Z-bosons can acquire mass for a short time.
One of the most mysterious bosons is the same Higgs boson, to detect traces of which, in fact, the Large Hadron Collider was built. This mysterious particle is believed to be one of the most abundant and important bosons in the Universe.
Back in the 1960s, English professor Peter Higgs proposed a hypothesis according to which all matter in the Universe was created by the interaction of various particles with some initial fundamental principle (resulting from the Big Bang), which was later named after him. He suggested that the Universe is permeated by an invisible field, passing through which some elementary particles are “overgrown” with some bosons, thereby acquiring mass, while others, such as photons, remain unencumbered by weight.
Scientists are now considering two possibilities - the existence of “light” and “heavy” variants. A “light” Higgs with a mass of 135 to 200 gigaelectronvolts should decay into pairs of W bosons, and if the boson mass is 200 gigaelectronvolts or more, then into pairs of Z bosons, which, in turn, generate pairs of electrons or muons.
It turns out that the mysterious Higgs boson is, as it were, the “creator” of everything in the Universe. Perhaps that is why Nobel laureate Leon Lederman once called it a “god particle.” But in the media this statement was somewhat distorted, and it began to sound like “a particle of God” or “a divine particle.”
How can one obtain traces of the presence of a “god particle”? It is believed that the Higgs boson can be formed during collisions of protons with neutrinos in the accelerator ring of the collider. In this case, as we remember, it must immediately decay into a number of other particles (in particular, Z-bosons), which can be registered.
True, detectors themselves cannot detect Z-bosons due to the extremely short lifetime of these elementary particles (about 3×10-25 seconds), but they can “catch” muons into which Z-bosons turn.
Let me remind you that a muon is an unstable elementary particle with a negative electric charge and spin ½. It is not found in ordinary atoms; before this it was found only in cosmic rays, which have speeds close to the speed of light. The lifetime of a muon is very short - it exists for only 2.2 microseconds, and then decays into an electron, an electron antineutrino and a muon neutrino.
Muons can be produced artificially by colliding a proton and a neutrino at high speeds. However, for a long time it was not possible to achieve such speeds. This was only possible during the construction of the Large Hadron Collider.
And finally the first results were obtained. During the experiment, which took place on October 10 this year, as a result of the collision of a proton with a neutrino, the birth of four muons was recorded. This proves that the appearance of two neutral gauge Z-bosons took place (they always appear during such events). This means that the existence of the Higgs boson is not a myth, but a reality.
However, scientists note that this event in itself does not necessarily indicate the birth of the Higgs boson, since other events can lead to the appearance of four muons. However, this is the first of these types of events that could eventually produce a Higgs particle. In order to speak with confidence about the existence of the Higgs boson in a particular mass range, it is necessary to accumulate a significant number of similar events and analyze how the masses of the resulting particles are distributed.
However, whatever you say, the first step towards proving the existence of a “god particle” has already been taken. Perhaps further experiments will be able to provide even more information about the mysterious Higgs boson. If scientists can finally “catch” it, then they will be able to recreate the conditions that existed 13 billion years ago after the Big Bang, that is, those under which our Universe was born.
| 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
Write a review about the article "Fundamental particle"
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
- //physics.ru
- //physics.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. |
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 | from 1.5 to 3 | d-quark (down-quark) / anti-d-quark | 4.79±0.07 | ||||
| 2 | c-quark (charm-quark) / anti-c-quark | 1250 ± 90 | s-quark (strange quark) / anti-s-quark | 95 ± 25 | ||||
| 3 | t-quark (top-quark) / anti-t-quark | 174 200 ± 3300 | b-quark (bottom-quark) / anti-b-quark | 4200 ± 70 | ||||
see also
Write a review about the article "Fundamental particle"
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
- //physics.ru
- //physics.ru
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particles
Excerpt characterizing the Fundamental ParticleThe gentlemen who visited Bilibin, secular, young, rich and cheerful people, formed a separate circle both in Vienna and here, which Bilibin, who was the head of this circle, called ours, les nftres. This circle, which consisted almost exclusively of diplomats, apparently had its own interests that had nothing to do with war and politics, interests of high society, relations with certain women and the clerical side of the service. These gentlemen, apparently, willingly accepted Prince Andrei into their circle as one of their own (an honor they did to few). Out of politeness, and as a subject for entering into conversation, he was asked several questions about the army and the battle, and the conversation again crumbled into inconsistent, cheerful jokes and gossip.
“But it’s especially good,” said one, telling the failure of a fellow diplomat, “what’s especially good is that the chancellor directly told him that his appointment to London was a promotion, and that he should look at it that way.” Do you see his figure at the same time?...
“But what’s worse, gentlemen, I give you Kuragin: the man is in misfortune, and this Don Juan, this terrible man, is taking advantage of it!”
Prince Hippolyte was lying in a Voltaire chair, his legs crossed over the arm. He laughed.
“Parlez moi de ca, [Come on, come on,]” he said.
- Oh, Don Juan! Oh snake! – voices were heard.
“You don’t know, Bolkonsky,” Bilibin turned to Prince Andrei, “that all the horrors of the French army (I almost said the Russian army) are nothing compared to what this man did between women.”
“La femme est la compagne de l"homme, [A woman is a man’s friend],” said Prince Hippolyte and began to look through the lorgnette at his raised legs.
Bilibin and our people burst out laughing, looking into Ippolit’s eyes. Prince Andrei saw that this Ippolit, whom he (had to admit) was almost jealous of his wife, was a buffoon in this society.
“No, I must treat you to Kuragin,” Bilibin said quietly to Bolkonsky. – He is charming when he talks about politics, you need to see this importance.
He sat down next to Hippolytus and, gathering folds on his forehead, started a conversation with him about politics. Prince Andrei and others surrounded both of them.
“Le cabinet de Berlin ne peut pas exprimer un sentiment d" alliance,” began Hippolyte, looking at everyone significantly, “sans exprimer... comme dans sa derieniere note... vous comprenez... vous comprenez... et puis si sa Majeste l"Empereur ne deroge pas au principe de notre alliance... [The Berlin cabinet cannot express its opinion on the alliance without expressing... as in its last note... you understand... you understand... however, if His Majesty the Emperor does not change the essence of our alliance...]
“Attendez, je n"ai pas fini...,” he said to Prince Andrei, grabbing his hand. “Je suppose que l”intervention sera plus forte que la non intervention.” Et...” He paused. – On ne pourra pas imputer a la fin de non recevoir notre depeche du 28 novembre. Voila comment tout cela finira. [Wait, I haven't finished. I think that intervention will be stronger than non-intervention. And... It is impossible to consider the matter over if our dispatch of November 28 is not accepted. How will this all end?]
And he let go of Bolkonsky’s hand, indicating that he had now completely finished.
“Demosthenes, je te reconnais au caillou que tu as cache dans ta bouche d"or! [Demosthenes, I recognize you by the pebble that you hide in your golden lips!] - said Bilibin, whose cap of hair moved on his head with pleasure .
Everyone laughed. Hippolytus laughed loudest of all. He apparently suffered, was suffocating, but could not resist the wild laughter that stretched his always motionless face.
“Well, gentlemen,” said Bilibin, “Bolkonsky is my guest in the house and here in Brunn, and I want to treat him, as much as I can, to all the joys of life here.” If we were in Brunn, it would be easy; but here, dans ce vilain trou morave [in this nasty Moravian hole], it is more difficult, and I ask you all for help. Il faut lui faire les honneurs de Brunn. [We need to show him Brunn.] You take over the theater, I – society, you, Hippolytus, of course – women.
– We need to show him Amelie, she’s lovely! - said one of ours, kissing the tips of his fingers.
“In general, this bloodthirsty soldier,” said Bilibin, “should be converted to more humane views.”
“I’m unlikely to take advantage of your hospitality, gentlemen, and now it’s time for me to go,” Bolkonsky said, looking at his watch.
- Where?
- To the emperor.
- ABOUT! O! O!
- Well, goodbye, Bolkonsky! Goodbye, prince; “Come to dinner earlier,” voices were heard. - We are taking care of you.
“Try to praise the order in the delivery of provisions and routes as much as possible when you speak with the emperor,” said Bilibin, escorting Bolkonsky to the front hall.
“And I would like to praise, but I can’t, as much as I know,” Bolkonsky answered smiling.
- Well, in general, talk as much as possible. His passion is audiences; but he himself does not like to speak and does not know how, as you will see.
Units of measurement of physical quantities when describing phenomena occurring in the microworld 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 SI and CGS units also use “natural systems of units” 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. The charge of a proton is equal in absolute value to the charge of an 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. 4 illustrates physical meaning spin J by analogy with the classical concept of angular momentum of a particle with mass m = 1 g moving with speed v = 1 cm/s in a circle with radius r = 1 cm. In classical physics, angular momentum J = mvr = L (L − orbital moment). 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 speed of the particle determines this the most 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), isotopic spin I and the 3rd projection of isotopic spin I 3, quark charge Q q /e and 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. An amazing 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 particle characteristics indicated in the table, important role for leptons, the lepton numbers play: 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 flavors of leptons participating 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 large group 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 presents 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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