home Tests For the first time, a particle consisting of three quarks of different families was discovered. Alpha (a) and beta (b) rays of radioactive radiation. The danger of alpha and beta radiation for the body Particles and prepositions

For the first time, a particle consisting of three quarks of different families was discovered. Alpha (a) and beta (b) rays of radioactive radiation. The danger of alpha and beta radiation for the body Particles and prepositions

They have been trying to find the Higgs boson for decades, but so far without success. Meanwhile, without it, the key provisions modern theory microcosms hang in the air.

The study of particles began not so long ago. In 1897, Joseph John Thomson discovered the electron, and 20 years later Ernest Rutherford proved that hydrogen nuclei are part of the nuclei of other elements, and later called them protons. In the 1930s, the neutron, muon and positron were discovered and the existence of the neutrino was predicted. At the same time, Hideki Yukawa built a theory of nuclear forces carried by hypothetical particles hundreds of times heavier than an electron, but much lighter than a proton (mesons). In 1947 traces of pi meson (pion) decays were found on photographic plates exposed to cosmic rays. Later, other mesons were discovered, and some of them are heavier than not only the proton, but also the helium nucleus. Physicists have also discovered many baryons, heavy and therefore unstable relatives of the proton and neutron. Once upon a time, all these particles were called elementary, but such terminology has long been outdated. Now only non-composite particles are considered elementary - fermions (with half spin - leptons and quarks) and bosons (with integer spin - carriers of fundamental interactions).

Elementary particles of the Standard Model

The fermion group (with half-integer spin) consists of leptons and quarks of the so-called three generations. Charged leptons are the electron and its massive counterparts the muon and the tau particle (and their antiparticles). Each lepton has a neutral partner in the face of one of the three varieties of neutrinos (also with antiparticles). The family of bosons, whose spin is 1, are particles that carry interactions between quarks and leptons. Some of them do not have mass and electric charge - these are gluons, which provide interquark bonds in mesons and baryons, and photons, quanta electromagnetic field. Weak interactions, manifested in the processes of beta decay, are provided by a trio of massive particles - two charged and one neutral.

The individual names of elementary and compound particles are usually not associated with the names of specific scientists. However, almost 40 years ago, another elementary particle was predicted, which was named after a living person, the Scottish physicist Peter Higgs. Like carriers of fundamental interactions, it has an integer spin and belongs to the class of bosons. However, its spin is not 1, but 0, and in this respect it has no analogues. For decades, they have been looking for it at the largest accelerators - the American Tevatron closed last year and the Large Hadron Collider, which is now operating, under the close attention of the world media. After all, the Higgs boson is very necessary for the modern theory of the microworld - the Standard Model of elementary particles. If it cannot be found, the key provisions of this theory will hang in the air.

Gauge symmetries

The beginning of the path to the Higgs boson can be counted from a short article published in 1954 by the Chinese physicist Yang Zhenning, who moved to the United States, and his colleague at the Brookhaven National Laboratory, Robert Mills. In those years, experimenters discovered more and more new particles, the abundance of which could not be explained in any way. In search of promising ideas, Yang and Mills decided to test the possibilities of a very interesting symmetry, which is subject to quantum electrodynamics. By that time, this theory had proved its ability to give excellent results in agreement with experience. True, in the course of some calculations, infinities appear there, but you can get rid of them using a mathematical procedure called renormalization.

Symmetry, which interested Yang and Mills, was introduced into physics in 1918 by the German mathematician Hermann Weyl. He called it a gauge, and this name has survived to this day. In quantum electrodynamics, gauge symmetry manifests itself in the fact that the wave function free electron, which is a vector with real and imaginary parts, can be continuously rotated at every point in spacetime (which is why the symmetry is called local). This operation (for formal language- a change in the phase of the wave function) leads to the fact that additives appear in the equation of motion of an electron, which must be compensated in order for it to remain valid. To do this, an additional term is introduced there, which describes the electromagnetic field interacting with the electron. The quantum of this field is a photon, a massless particle with a unit spin. Thus, the existence of photons (as well as the constancy of the electron charge) follows from the local gauge symmetry of the free electron equation. We can say that this symmetry dictates that the electron interact with the electromagnetic field. Any phase shift becomes an act of such an interaction - for example, the emission or absorption of a photon.

The relationship between gauge symmetry and electromagnetism was discovered as early as the 1920s, but did not arouse much interest. Yang and Mills were the first to use this symmetry to construct equations describing particles of a different nature than the electron. They took up the two "oldest" baryons - the proton and the neutron. Although these particles are not identical, in relation to nuclear forces they behave almost identically and have almost the same mass. In 1932, Werner Heisenberg showed that the proton and neutron can formally be considered different states of the same particle. To describe them, he introduced a new quantum number - the isotopic spin. Since the strong force does not distinguish between protons and neutrons, it conserves the total isotopic spin, just as the electromagnetic force conserves electric charge.

Yang and Mills wondered which local gauge transformations preserve isospin symmetry. It was clear that they could not coincide with the gauge transformations of quantum electrodynamics, if only because we were already talking about two particles. Young and Mills analyzed the totality of such transformations and found that they generate fields whose quanta supposedly carry the interactions between protons and neutrons. There were three quanta in this case: two charged (positively and negatively) and one neutral. They had zero mass and unit spin (that is, they were vector bosons) and traveled at the speed of light.

The theory of B-fields, as the co-authors dubbed them, was very beautiful, but did not stand the test of experience. The neutral B-boson could be identified with the photon, but its charged counterparts were left out. According to quantum mechanics, only sufficiently massive virtual particles can be mediators in the transfer of short-range forces. The radius of nuclear forces does not exceed 10–13 cm, and the massless Yang and Mills bosons clearly could not claim to be their carriers. In addition, experimenters have never detected such particles, although in principle charged massless bosons are easy to detect. Yang and Mills proved that local gauge symmetries "on paper" could generate force fields of a non-electromagnetic nature, but the physical reality of these fields was pure conjecture.

Electroweak duality

The next step towards the Higgs boson was taken in 1957. By that time, theorists (the same Yang and Li Zundao) assumed, and the experimenters proved, that parity is not conserved in beta decays (in other words, mirror symmetry is violated). This unexpected result interested many physicists, among whom was Julian Schwinger, one of the founders of quantum electrodynamics. He hypothesized that weak interactions between leptons (science had not yet reached quarks!) are carried by three vector bosons - a photon and a pair of charged particles similar to B-bosons. It followed that these interactions are in partnership with electromagnetic forces. Schwinger did not deal with this problem anymore, but suggested it to his graduate student Sheldon Glashow.

The work spanned four years. After a number of unsuccessful attempts, Glashow constructed a model of the weak and electromagnetic interactions based on the unification of the gauge symmetries of the electromagnetic field and the Yang and Mills fields. In addition to the photon, it featured three more vector bosons - two charged and one neutral. However, these particles again had zero mass, which created a problem. The radius of a weak interaction is two orders of magnitude smaller than that of a strong one, and it all the more requires very massive mediators. In addition, the presence of a neutral carrier required the possibility of beta transitions that do not change the electric charge, and at that time such transitions were not known. Because of this, after publishing his model in late 1961, Glashow lost interest in unifying the weak and electromagnetic forces and switched to other topics.

Schwinger's hypothesis also interested the Pakistani theorist Abdus Salam, who, together with John Ward, built a model similar to Glashow's. He also encountered the masslessness of gauge bosons and even came up with a way to eliminate it. Salam knew that their masses could not be entered "by hand" as the theory became non-normable, but he hoped to get around this difficulty by spontaneous symmetry breaking, so that the solutions to the equations of motion of bosons did not have the gauge symmetry inherent in the equations themselves. With this task, he interested the American Steven Weinberg.

But in 1961, the English physicist Geoffrey Goldstone showed that in relativistic quantum field theories, spontaneous symmetry breaking seems to inevitably produce massless particles. Salam and Weinberg tried to disprove Goldstone's theorem, but only strengthened it in their own work. The riddle looked unsolvable, and they turned to other areas of physics.

Higgs and others

Help came from specialists in condensed matter physics. In 1961, Yoichiro Nambu noted that when a normal metal goes into a superconducting state, the former symmetry is spontaneously broken, but no massless particles appear. Two years later, Philip Anderson, using the same example, noted that if the electromagnetic field does not obey the Goldstone theorem, then the same can be expected from other gauge fields with local symmetry. He even predicted that the Goldstone bosons and the Yang and Mills field bosons could somehow cancel each other out, leaving behind massive particles.

This prediction turned out to be prophetic. In 1964 it was acquitted by François Englert and Roger Broat, physicists at the Free University of Brussels, Peter Higgs and Jerry Guralnik, Robert Hagen and Thomas Kibble at Imperial College London. Not only did they show that the conditions for the applicability of the Goldstone theorem are not met in Yang–Mills fields, but they also found a way to provide excitations of these fields with a nonzero mass, which is now called the Higgs mechanism.

These wonderful works were noticed and appreciated by no means immediately. It was only in 1967 that Weinberg built a unified model of the electroweak interaction, in which the trio of vector bosons gain mass based on the Higgs mechanism, and Salam did the same a year later. In 1971, the Dutch Martinus Veltman and Gerard "t Hooft proved that this theory is renormalizable and therefore has a clear physical meaning. She firmly stood on her feet after 1973, when in a bubble chamber Gargamelle(CERN, Switzerland) experimenters registered the so-called weak neutral currents, indicating the existence of an uncharged intermediate boson (direct registration of all three vector bosons was carried out at CERN only in 1982–1983). Glashow, Weinberg and Salam got it for her Nobel Prizes in 1979, Veltman and "t Hooft - in 1999. This theory (and with it the Higgs boson) has long been an integral part of the Standard Model of elementary particles.

Higgs mechanism

The Higgs mechanism is based on scalar fields with spinless quanta - Higgs bosons. They are believed to have arisen moments after big bang and now fill the entire universe. Such fields have the lowest energy at a non-zero value - this is their stable state.

It is often written that elementary particles gain mass as a result of braking by the Higgs field, but this is an overly mechanistic analogy. The electroweak theory involves four Higgs fields (each with its own quanta) and four vector bosons - two neutral and two charged, which themselves have no mass. Three bosons, both charged and one neutral, each absorb one Higgs and as a result acquire mass and the ability to carry short-range forces (they are denoted by the symbols W + , W - and Z 0). The last boson does not absorb anything and remains massless - it is a photon. "Eaten" Higgs are unobservable (physicists call them "spirits"), while their fourth cousin should be observed at energies sufficient for its birth. In general, these are exactly the processes that Anderson managed to predict.

elusive particle

The first serious attempts to catch the Higgs boson were made at the turn of the 20th and 21st centuries at the Large Electron-Positron Collider ( Large Electron-Positron Collider, LEP) at CERN. These experiments were truly the swan song of a remarkable facility, on which the masses and lifetimes of heavy vector bosons were determined with unprecedented accuracy.

The Standard Model makes it possible to predict the channels of creation and decay of the Higgs boson, but it does not make it possible to calculate its mass (which, by the way, arises from its ability to self-force). According to the most general estimates, it should not be less than 8–10 GeV and more than 1000 GeV. By the beginning of the sessions at LEP, most physicists believed that the most likely range was 100–250 GeV. The LEP experiments raised the lower threshold to 114.4 GeV. Many experts believed and still believe that if this accelerator had worked longer and increased the energy of colliding beams by ten percent (which was technically possible), the Higgs boson could have been registered. However, the CERN leadership did not want to delay the launch of the Large Hadron Collider, which was to be built in the same tunnel, and at the end of 2000 LEP was closed.

Boson pen

Numerous experiments, one after the other, ruled out the possible mass ranges of the Higgs boson. The lower threshold was set at the LEP accelerator - 114.4 GeV. At the Tevatron, masses exceeding 150 GeV were ruled out. Later, the mass ranges were refined to 115–135 GeV, and the upper limit was shifted to 130 GeV at CERN at the Large Hadron Collider. So the Higgs boson of the Standard Model, if it exists, is locked into fairly narrow mass bounds.

The next search cycles were carried out at the Tevatron (on the CDF and DZero detectors) and at the LHC. As Dmitry Denisov, one of the leaders of the DZero collaboration, told PM, Tevatron began collecting statistics on Higgs in 2007: “Although there was enough energy, there were many difficulties. The collision of electrons and positrons is the "cleanest" way to catch the Higgs, because these particles do not have an internal structure. For example, during the annihilation of a high-energy electron-positron pair, a Z 0 -boson is born, which emits the Higgs without any background (however, in this case, even dirtier reactions are possible). We, on the other hand, collided protons and antiprotons, loose particles consisting of quarks and gluons. So the main task is to highlight the birth of the Higgs against the background of many similar reactions. A similar problem exists for the LHC teams.”

Traces of unseen beasts

There are four main ways (as physicists say, channels) for the birth of the Higgs boson.

The main channel is the fusion of gluons (gg) in the collision of protons and antiprotons, which interact through loops of heavy top quarks.
The second channel is the fusion of virtual vector bosons WW or ZZ(WZ) emitted and absorbed by quarks.
The third channel for the production of the Higgs boson is the so-called associative production (together with the W or Z boson). This process is sometimes called Higgsstrahlung(similar to the German term bremsstrahlung- bremsstrahlung).
And finally, the fourth one is the fusion of a top quark and an antiquark (associative production together with top quarks, tt) from two top quark-antiquark pairs generated by gluons.

“In December 2011, new messages came from the LHC,” Dmitry Denisov continues. - They were looking for Higgs decays either on top-quark and its antiquark, which annihilate and turn into a pair of gamma quanta, or into two Z 0 -bosons, each of which decays into an electron and a positron or a muon and an antimuon. The data obtained suggest that the Higgs boson pulls about 124–126 GeV, but this is not enough for final conclusions. Now both our collaborations and physicists at CERN continue to analyze the results of experiments. It is possible that we and they will soon come to new conclusions, which will be presented on March 4 at an international conference in the Italian Alps, and I have a presentiment that you will not be bored there.”

The Higgs boson and the end of the world

So, this year we can expect either the discovery of the Higgs boson of the Standard Model, or its cancellation, so to speak. Of course, the second option will create a need for new physical models, but the same can happen in the first case! In any case, one of the most authoritative experts in this field, John Ellis, professor at King's College London, thinks so. In his opinion, the discovery of a "light" (not more massive than 130 GeV) Higgs boson will create an unpleasant problem for cosmology. It will mean that our Universe is unstable and someday (perhaps even at any moment) will move into a new state with less energy. Then the end of the world will happen - in the very full meaning this word. It remains to be hoped that either the Higgs boson will not be found, or Ellis is mistaken, or the Universe will delay the suicide a little.

1.2. Properties β -radiation

Beta radiation ( b -particles) is a stream of electrons (positrons), each of which has a charge equal to one elementary charge, 4.8 × 10 - 10 CGSE electrostatic units or 1.6 10 -19 coulombs. rest mass b -particle is equal to 1/1840 of the elementary mass of a hydrogen atom, (7000 times less than the mass α -particles) or in absolute units 9.1 × 10 -28 g. Since b particles move at a speed much greater than α -particles equal to » 0.988 (Einstein's mass) of the speed of light, then their mass should be calculated according to the relativistic equation:

where then - rest mass (9.1 10 -28 g);

V - speed β -particles;

C is the speed of light.

For the fastest β -particles m ≈ 16 m o .

When emitting one b -particles the serial number of the element increases (emission of an electron) or decreases (emission of a positron) by one. Beta decay is usually accompanied by g -radiation. Each radioactive isotope emits an aggregate b -particles of very different energies, which, however, do not exceed a certain maximum energy characteristic of a given isotope.

Energy Spectra b -radiation are shown in fig. 1.5, 1.6. In addition to the continuous spectrum of energies, some radioelements are characterized by the presence of a line spectrum associated with the extraction of secondary electrons by g-quanta from the electron orbits of the atom (the phenomenon of internal conversion). This happens when β - decay goes through an intermediate energy level, and excitation can be removed not only by emitting γ -quantum, but also by knocking out an electron from the inner shell.

However, the number b -particles corresponding to these lines are small.

The continuity of the beta spectrum is explained by the simultaneous emission b -particles and neutrinos.

p = n + β + + η(neutrino)

n = p + β - + η(antineutrino)

The neutrino takes on some of the beta decay energy.

Average energy b -particle is equal to 1/3. E max and fluctuates between 0.25–0.45 E max for various substances. Between the maximum energy E max b -radiation and decay constant l element Sergent established the ratio (for E max > 0.5 Mev),

l = k∙E 5 max (1.12)

Thus, for β - radiation energy β -particles are larger, the shorter the half-life. For example:

Pb 210 (RaD) T = 22 years, E max = 0.014 MeV;

Bi 214 (RaC) T = 19.7 months, E max = 3.2 MeV.

1.2.1. Interaction β - radiation with matter

When interacting β –particles with matter are possible following cases:

a) Ionization of atoms. It is accompanied by characteristic radiation. Ionization ability β -particles depends on their energy. Specific ionization is the greater, the less energy β -particles. For example, with energy β -particles 0.04 MeV 200 pairs of ions are formed per 1 cm of the path; 2 MeV - 25 pairs; 3 MeV - 4 pairs.

b) Excitation of atoms. It is typical for β -particles with high energy, when the interaction time β -particles with an electron are few and the probability of ionization is small; in this case β -particle excites an electron, the excitation energy is removed by emitting characteristic x-rays, and in scintillators, a significant part of the excitation energy manifests itself in the form of a flash - scintillation (ie, in the visible region).

c) Elastic scattering. Occurs when the electric field of the nucleus (electron) deflects β -particle, while the energy β -particles do not change, only the direction changes (by a small angle);

d) Electron deceleration in the Coulomb field of the nucleus. This gives rise to electromagnetic radiation with the greater energy, the greater the acceleration experienced by the electron. Since individual electrons experience different accelerations, the bremsstrahlung spectrum is continuous. The energy loss for bremsstrahlung is determined by the expression: the ratio of energy losses for bremsstrahlung to the losses for excitation and ionization:

Thus, losses and bremsstrahlung are significant only for high electron energies with large atomic numbers.

For most β -particles, the maximum energy lies in the range of 0.014–1.5 MeV, we can assume that for 1 cm of the path β -particles form 100 - 200 pairs of ions. α -particle per 1 cm path forms 25 - 60 thousand pairs of ions. Therefore, we can assume that the specific ionization capacity β- radiation is two orders of magnitude smaller than that of α-radiation. Less ionization - energy is lost more slowly, since the ionization power (and the probability of excitation) β -particles are 2 orders of magnitude smaller, which means that it slows down 2 orders of magnitude slower, i.e., approximately the run β -particles are 2 orders of magnitude larger than for α- particles. 10 mg / cm 2 100 \u003d 1000 mg / cm 2 ≈ 1 g / cm 2.

beta particle

beta particle(β particle), a charged particle emitted by beta decay. The stream of beta particles is called beta rays or beta radiation.

Negatively charged beta particles are electrons (β -), positively charged - positrons (β +).

Beta rays should be distinguished from the secondary and tertiary electrons produced as a result of air ionization - the so-called delta rays and epsilon rays.

Properties

The energies of beta particles are distributed continuously from zero to some maximum energy, depending on the decaying isotope; this maximum energy ranges from 2.5 keV (for rhenium-187) to tens of MeV (for short-lived nuclei far from the beta stability line).

Radioactivity

Significant doses of external beta radiation can cause radiation burns to the skin and lead to radiation sickness. Even more dangerous is internal exposure from beta-active radionuclides that have entered the body. Beta radiation has a significantly lower penetrating power than gamma radiation (however, an order of magnitude greater than alpha radiation). A layer of any substance with a surface density of about 1 g/cm 2 (for example, a few millimeters of aluminum or a few meters of air) almost completely absorbs beta particles with an energy of about 1 MeV.

Classification

By life time

Stable elementary particles are particles that have infinite big time life in a free state (proton, electron, neutrino, photon and their antiparticles).
Unstable elementary particles - particles that decay into other particles in a free state for end time(all other particles).

By weight

All elementary particles are divided into two classes:

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

The size of the back

All elementary particles are divided into two classes:

By type of interaction

Elementary particles are divided into the following groups:

Composite particles

Hadrons are particles involved in all kinds of fundamental interactions. They consist of quarks and are subdivided, in turn, into:
- mesons - hadrons with integer spin, that is, being bosons;
- baryons are hadrons with half-integer spin, i.e. fermions. These include, in particular, the particles that make up the nucleus of the atom - proton and neutron.

Fundamental (structureless) particles

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

Sizes of elementary particles

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

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

Story

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

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

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

standard model

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

Fermions

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

Generations of particles

First generation	Second generation	third generation
Electron: e-	Muon: μ −	Tau lepton: τ −
Electron neutrino: v e	Muon neutrino: ν μ	Tau neutrino: ν τ (\displaystyle \nu _(\tau ))
u-quark ("top"): u	c-quark ("enchanted"): c	t-quark ("true"): t
d-quark ("bottom"): d	s-quark ("strange"): s	b-quark ("charming"): b

antiparticles

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

antiparticles

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

Quarks

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