Standard model of elementary particles for beginners. FAQ: Standard model Standard model of interaction of elementary particles

A modern idea of \u200b\u200bparticle physics is contained in the so-called Standard model . The standard model (cm) of particle physics is based on quantum electrodynamics, quantum chromodynamics and a quark-partton model.
Quantum electrodynamics (CAD) - high-precision theory - describes the processes occurring under the action of electromagnetic forces that are studied with a high degree of accuracy.
Quantum chromodynamics (QCD) describing the processes of strong interactions, is built by analogy with the CAD, but is more a semi-empirical model.
The quark-partton model combines theoretical and experimental results of studies of the properties of particles and their interactions.
Until now, deviations are not detected from the standard model.
The main content of the standard model is presented in Tables 1, 2, 3. Constituents of matter are three generations of fundamental Fermi ones (I, II, III), whose properties are listed in Table. 1. Fundamental bosons - interaction carriers (Table 2), which can be submitted using a Feynman diagram (Fig. 1).

Table 1: Fermions - (spin semi-free in units ћ) Constitutions of matter

Table 2: Bosons - interaction carriers (spin \u003d 0, 1, 2 ... in units ћ)

Table 3: Comparative characteristics of fundamental interactions

The strength of the interaction is relatively strong.

Fig. 1: Feynman diagram: A + B \u003d C + D, A - interaction constant, Q 2 \u003d -t - 4-pulse, which particle A transmits a particle as a result of one of the four types of interactions.

1.1 Basic positions of the standard model

• Adrons consist of quarks and gluons (partons). Quarks - fermions with spin 1/2 and mass M 0; Gluions - bosons with spin 1 and mass M \u003d 0.
• Quarks are classified on two signs: aroma and color. It is known 6 flavors of quarks and 3 colors for each quark.
• Aroma is a characteristic that persists in strong interactions.
• The gluon is composed of two colors - colors and antituettes, and all other quantum numbers are equal to zero. When emissing the gluon quark changes color, but not fragrance. Total works 8 gluons.
• Elementary processes in the CCD are built by analogy with the CAD: the braking emission of the gluone quark, the birth of kilk-anti-coaching pairs of gluons. The process of birth of gluons with gluons has no analogue in the CAD.
• A static gluon field does not tend to zero at infinity, i.e. The total energy of such a field is infinite. Thus, quarks cannot fly out of the hadrons, there is a confinement.
• The forces of attraction that have two unusual properties are acting: a) asymptotic freedom at very low distances and b) infrared captivity - a confinement, due to the fact that the potential energy of the interaction V (R) is increasingly growing with increasing distance between quarks R, V (R ) \u003d -α S / R + æR, α s and æ - constants.
• Quark-quark interaction is not additive.
• Only color singlets may exist in the form of free particles:
  The meson singlet for which the wave function is determined by the ratio

and baryon singlet with a wave function

where R is red, in - blue, G is green.

• There are current and component quarks that have different masses.
• The cross sections of the process A + B \u003d C + x with the exchange of one gluon between quarks, part of the administs, are written in the form:

ŝ \u003d x a x b s, \u003d x a t / x c.

Symbols A, B, C, D are indicated by quarks and related variables, symbols A, B, C - hadron, ŝ ,,, - values \u200b\u200brelated to quarks - the function of the distribution of quarks and in the adjone A (or, respectively, - Quarks B in River B), - Fragment Fragmentation FIRL C. C, D / DT is an elementary section qq interaction.

1.2 Search for deviations from the standard model

With existing energies of accelerated particles, all CHD positions are well performed and the more the CED. In the planned experiments with higher particle energies of one of the main tasks, the search for deviations from the standard model is considered.
Further development of high-energy physics is associated with the solution of the following tasks:

1. The search for exotic particles having a structure other than adopted in the standard model.
2. Search for neutrino oscillations ν μ ↔ ν τ and the associated problem of neutrino mass (ν m ≠ 0).
3. The search for the collapse of the proton, the lifetime of which is estimated by the value of τ exploiting\u003e 10 33 years.
4. Finding the structure of fundamental particles (strings, cones at distances D< 10 -16 см).
5. Detection of deconfinmed hadron matter (quark gluon plasma).
6. The study of the violation of CP invariance during the decay of neutral K-mesons, D-mesons and B-particles.
7. The study of the nature of dark matter.
8. Studying the composition of vacuum.
9. Higgs-bosona search.
10. Search for supersymmetric particles.

1.3 Unresolved Questions of the Standard Model

The fundamental physical theory, the standard model of electromagnetic, weak and strong interactions of elementary particles (quarks and leptons) is the generally accepted achievement of the physics of the 20th century. She explains all the well-known experimental facts in microworld physics. However, there are a number of questions that in the standard model there is no answer.

1. The nature of the mechanism of spontaneous violation of electrical closure of calibration invariance is unknown.

• An explanation of the existence of masses in W ± - and z 0 -Bosons requires introducing into the theory of scalar fields with non-invariant relative to calibration transformations by the main state of -vacuum.
• The consequence of this is the emergence of a new scalar particle - Boson Higgs.

1. Cm does not explain the nature of quantum numbers.

• What is charges (electric; baryon; lepton: le, l μ, l τ: color: blue, red, green) and why are they quantized?
• Why there are 3 generations of fundamental fermions (I, II, III)?

1. SM does not include gravity, hence the path to inclusion of gravity in cm - a new hypothesis about the existence of additional measurements in the micromyr space.
2. There is no explanation, why the fundamental scale of the bar (M ~ 10 19 GeV) is so far from the fundamental scale of electrical interactions (M ~ 10 2 2 GeV).

Currently there has been a way to solve these problems. It consists in the development of a new idea of \u200b\u200bthe structure of fundamental particles. It is assumed that the fundamental particles are objects that are called "strings". The properties of strings are discussed in a rapidly developing model of superstrun, which claims to establish a connection between the phenomena occurring in the physics of elementary particles and in astrophysics. Such a link led to the formulation of a new discipline - cosmology of elementary particles.

What a stupid name for the most accurate scientific theory of all famous humanity. More than a quarter of the Nobel Prizes in the Physics of the last century were awarded to work, which either directly or indirectly related to the standard model. The name of her, of course, it seems that a couple of hundred rubles you can buy an improvement. Any theoretical physicist would prefer "an amazing theory of almost everything", which is, actually, and is.

Many people remember the excitement among scientists and in the media caused by the opening of the Higgs boson in 2012. But his discovery did not make a surprise and did not arise from nowhere - it marked the fiftieth anniversary of the victories of the standard model. It includes each fundamental force except gravity. Any attempt to refute it and demonstrate in the laboratory that it needs to be completely recycled - and there was a lot of such - failed.

In short, the standard model is responsible for this question: what is everything made and how it all keeps together?

The smallest building blocks

Physics love simple things. They want to crush everything until the very essence, find the most basic building blocks. Do this in the presence of hundreds of chemical elements is not so easy. Our ancestors believed that everything consists of five elements - earth, water, fire, air and ether. Five is much easier than hundred eighteen. And also incorrect. You certainly know that the world around us consists of molecules, and molecules consist of atoms. Chemist Dmitry Mendeleev found out in the 1860s and presented atoms in the table of elements, which is studied today at school. But these chemical elements 118. Antimony, arsenic, aluminum, selenium ... and 114 more.

In 1932, scientists knew that all these atoms consist of only three particles - neutrons, protons and electrons. Neutrons and protons are closely connected with each other in the core. Electrons, thousands of times lighter than them, circle around the core at speed close to the light. Physics Plank, Bor, Schrödinger, Heisenberg and others presented a new science - quantum mechanics - to explain this movement.

This would be great to stay. Total three particles. It is even easier than five. But how do they hold together? Negatively charged electrons and positively charged protons are fastening together by electromagnetism. But the protons are knocked down in the core and their positive charges should sweep them away. Even neutral neutrons will not help.

What binds these protons and neutrons together? "Divine intervention"? But even the Divine Being would deliver the problems for each of the 1080 protons and neutrons in the universe, while holding their will.

Expanding the zoo of particles

Meanwhile, nature desperately refuses to keep only three particles in its zoo. Even four, because we need to take into account the photon, the light particle described by Einstein. Four turned into five when Anderson measured electrons with a positive charge - positrons - which beat on the ground from the external space. Five have become six when the peony was detected, holding the kernel as a whole and the predicted Yukow.

Then muon appeared - 200 times heavier than an electron, but in the rest of his twin. This is seven. Not so simple.

By the 1960s there were hundreds of "fundamental" particles. Instead of a well-organized periodic table, there were only long lists of barions (heavy particles like protons and neutrons), mesons (like Yukawa peonies) and leptons (light particles, such as an electron and elusive neutrino), without any organization and principles of the device.

And the standard model was born in this junk. There was no insight. Archimeda did not jumped out of the bathroom with a cry of "Eureka!". No, instead in the mid-1960s, several smart people put forward important assumptions that turned this bog first in a simple theory, and then fifty years of experimental verification and theoretical development.

Quark. They received six options that we call flavors. As in colors, only not so tasty smelling. Instead of roses, lilies and lavender, we got upper and lower, strange and enchanted, adorable and true quarks. In 1964, Gell-Mann and Collegu taught us to mix three quarts to get Barion. Proton is two top and one lower quark; Neutron - two lower and one top. Take one quark and one antiquarian - get the meson. Peony is the upper or lower quark associated with the upper or lower antiquarian. All the substance with which we are dealing with the upper and lower quarks, antiquark and electrons.

Simplicity. Although not quite simplicity, because it is not easy to hold quarks connected. They join themselves so tightly that you will never find a quark or antiquarian wandering by itself. The theory of this connection and particles that take part in it, namely gluons, is called quantum chromodynamics. This is an important part of the standard model, mathematically complicated, and even unreserved for basic mathematics. Physicists are doing everything possible to produce calculations, but sometimes the mathematical apparatus is not well developed.

Another aspect of the standard model is the "Lepton Model". This is the name of the most important article in 1967, written by Stephen Weinberg, which united quantum mechanics with the most important knowledge of how particles interact, and organized them into a single theory. He turned on electromagnetism, tied it with a "weak force", which leads to certain radioactive decays, and explained that these are different manifestations of the same force. This model included the Higgs mechanism, which gives a mass of fundamental particles.

Since then, the standard model predicted the results of experiments for the results, including the discovery of several types of quarks and W- and Z-bosons - heavy particles, which in weak interactions perform the same role as the photon in electromagnetism. The likelihood that neutrino has a mass was missed in the 1960s, but confirmed the standard model in the 1990s, after a few decades.

The detection of the Higgs boson in 2012, which has long been predicted by the standard model and the long-awaited, not, nevertheless, surprise. But it was another important victory of the standard model over the dark forces, which are regularly waiting for particle physics on the horizon. Physics do not like that the standard model does not correspond to their ideas about the simple, they are concerned about its mathematical inconsistency, and also seek the opportunity to enable gravity into the equation. Obviously, it is poured into different theories of physics, which may be after the standard model. So there were theories of great association, supersymmetry, technocolor and string theory.

Unfortunately, the theory beyond the standard model did not find successful experimental confirmations and serious bars in the standard model. Fifty years later, it is the standard model closest to the status of the theory of all. Amazing theory almost everything.

Today, the standard model is one of the most important theoretical structures in the physics of elementary particles describing the electromagnetic, weak and strong interaction of all elementary particles. The main provisions and components of this theory describes the physicist, a corresponding member of the Russian Academy of Sciences Mikhail Danilov

1

Now, based on experimental data, a very perfect theory has been created, which describes almost all the phenomena that we observe. This theory is modestly called the "standard model of elementary particles". It has three generations of fermions: quarks, leptons. This is so to speak, building material. From the first generation, all we see around us are built. It includes u- and d-quarks, electron and electron neutrino. Protons and neutrons consist of three quarks: UUD and UDD, respectively. But there are two more generations of quarks and leptons, which to some extent repeat the first, but heavier and in the end decompose on the particles of the first generation. All particles have antiparticles with opposing charges.

2

The standard model includes three interactions. Electromagnetic interaction holds electrons within an atom and atoms inside molecules. The carrier of electromagnetic interaction is photon. The strong interaction holds protons and neutrons inside the atomic nucleus, and quarks within protons, neutrons and other hadrons (so L. B. Okun offered to call particles involved in strong interaction). In strong interaction, the quarks and constructed cameras, as well as the carryers of the interaction itself - gluons (from English Glue - gluons). The hadrons consist either of three quarks, as a proton and neutron, or from quark and antiquark, as, say, π ± meson consisting of U- and anti-d-quarks. Weak interaction leads to rare decays, such as the neutron decay per proton, electron and electron antineutrino. The carriers of weak interaction are W- and Z-bosons. The quarks and leptons take part in weak interaction, but it is very small at our energies. This, however, is explained simply a large mass of W- and Z-bosons, which are two orders of magnitude harder protons. At energies, more than the mass of W-and Z-bosons, the power of electromagnetic and weak interaction becomes comparable, and they are combined into a single electroweavy interaction. It is assumed that with much b aboutleather energies and strong interaction will unite with the rest. In addition to electrical and strong interactions there is still a gravitational interaction that is not included in the standard model.

W, z-bosons

g - Gluions

H0 - Boson Higgs.

3

The standard model can be formulated only for massless fundamental particles, i.e. quarks, leptons, W- and Z-bosons. In order for them to purchase a mass, the Higgs field is usually introduced, named by one of the scientists who proposed this mechanism. In this case, in the standard model there must be another fundamental particle - Boson Higgs. The search for this last brick in a slim building of the standard model is actively conducted on the largest collider in the world - the Great Hellon Collider (Tank). Already obtained guidance on the existence of a higgs boson with a mass of about 133 mass proton. However, the statistical reliability of these instructions is still insufficient. It is expected that by the end of 2012, the situation will become clearer.

4

The standard model perfectly describes almost all experiments on the physics of elementary particles, although the search for phenomena leaving beyond the frames is persistently underway. The last hint of physics beams beam was discovered in 2011 in the LHCB experiment on the tank of unexpectedly large differences in the properties of the so-called placed mesons and their anti-patse. However, apparently, even such a great difference can be explained within the framework On the other hand, in 2011 another, seized several decades, confirmation of cm, predicting the existence of exotic hadrons. Physics from the Institute of Theoretical and Experimental Physics (Moscow) and the Institute of Nuclear Physics (Novosibirsk) within the framework of the International Experiment, Belle found hadrons consisting of two quarks and two antiquarks. Most likely, these are molecules of mesons, predicted by theoretics ITEF M. B. Voloshin and L. B. Okube.

5

Despite all the successes of the standard model, it has many drawbacks. The number of free parameters of the theory exceeds 20, and completely unclear, where their hierarchy arises from. Why is the mass of t-quark 100 thousand times more u-quark mass? Why is the connection constant T- and D-quarks, first measured in the International Experiment of Argus in the active participation of ITEF physicists, 40 times less than the connection constant of C- and D-quarks? For these issues, see the CM does not give a response. Finally, why do you need 3 generations of quarks and leptons? Japanese theorists M. Kobayashi and T. Maskawa in 1973 showed that the existence of 3-generation quarks makes it possible to explain the difference in the properties of matter and antimatter. The hypothesis of M.Kobayashi and T. Maskawa was submitted in Belle and Babar experiments with the active participation of physicists from the ITAF and ITEF. In 2008, M. Kobayashi and T. Maskawa were awarded for their theory of the Nobel Prize

6

The standard model has more fundamental problems. We now know that see is not complete. From astrophysical studies, it is known that there is a matter, which is not in see. This is the so-called dark matter. It is about 5 times more than ordinary matter from which we are. Perhaps the main disadvantage of the standard model is the absence of internal self-consistency in it. For example, the natural mass of the Higgs boson arising from the CM due to the exchange of virtual particles, for many orders of magnitude exceeds the mass required to explain the observed phenomena. One of the outputs, the most popular at the moment is the hypothesis of supersymmetry - the assumption that there is symmetry between fermions and bosons. For the first time this idea was expressed in 1971. Yu. A. Golfand and E. P. Lichtman in Fiana, and now it enjoys enormous popularity.

7

The existence of supersymmetric particles not only allows you to stabilize the behavior of cm, but also gives a very natural candidate for the role of dark matter - the easiest supersymmetric particle. Although at the moment there are no reliable experimental confirmations of this theory, it is so beautiful and so elegant allows you to solve the problems of the standard model that many people believe in it. The tank is actively searching for supersymmetric particles and other alternatives see. For example, it is searched for additional measurements of space. If they exist, many problems can be solved. Perhaps gravity becomes strong in relatively long distances, which will also be a big surprise. Other, alternative Higgs models, mass mechanisms for fundamental particles are possible. Search for effects beyond the standard model is carried out very actively, but so far unsuccessfully. A lot should be cleared in the coming years.

"We will be asked why the group of talented and devoted to their work of people is ready to dedicate life to pursuit of such tiny objects that can not even see? In fact, human curiosity and desire to learn how the world in which we live are arranged in the classroom of physicists of elementary particles.

If you are still afraid of the phrase quantum mechanics and still do not know what the standard model is - Welcome to Cat. In my publication, I will try as simply and clearly explain the basics of the quantum world, as well as the physics of elementary particles. We will try to figure out what the main differences of fermions and bosons, why quarks have such strange names, and finally, why everyone wanted to find Boson Higgs.

What are we consisting of?

Well, our journey into the microworld, we will start with an imperious question: what are the items around us? Our world, like a house, consists of a variety of small bricks, which in a special way connecting, create something new, not only in appearance, but also in their properties. In fact, if you look close to them, you can find that different types of blocks are not so much, just every time they connect with each other in different ways, forming new forms and phenomena. Each block is an indivisible elementary particle, which will be discussed in my story.

For example, take some substance, let it be with us will be the second element of the periodic Mendeleev system, inert gas, helium. Like the remaining substances in the universe, helium consists of molecules, which in turn is formed by the bonds between atoms. But in this case, for us, helium is a little special, because it consists of only one atom.

What is the atom?

The helium atom, in turn, consists of two neutrons and two protons constituting the atomic nucleus, around which two electrons rotate. The most interesting thing is that absolutely indivisible here is only electron.

Interesting moment of quantum world

Than less the mass of the elementary particle, the more It takes place. It is for this reason that electrons that are eleven than 2000 times the proton occupy much more space compared to the atom's core.

Neutrons and protons belong to the so-called group herrons (particles exposed to strong interaction), and if more accurately, barionov.

Hadrons can be divided into groups

• Barionov, which consist of three quarks
• Mesons that consist of a pair: antiparticle particle

Neutron, as clear of his name, is neutrally charged, and can be divided into two lower quarts and one top quark. Proton, positively charged particle, is divided into one lower quark and two upper quarts.

Yes, yes, I'm not kidding, they are really called the upper and lower. It would seem that if we opened the upper and lower quark, and even an electron, we can be able to describe the whole universe with them. But this statement would be very far from the truth.

The main problem - particles must somehow interact with each other. If the world consisted only from this trinity (neutron, proton and electron), then the particles would simply flew along the endless spaces of space and would never have been going to larger formations, like hadrons.

Fermions and bosons

For a long time, scientists were invented a convenient and concise form of the representation of elementary particles, called the standard model. It turns out that all elementary particles are divided into fermions, of which the whole matter is, and bosonswhich transfer various types of interactions between fermions.

The difference between these groups is very visual. The fact is that fermions for survival under the laws of the quantum world require some space, while their colleagues - bosons can be quietly trillion to live right on each other.

Fermions

A group of Fermionov, as it was already said, creates visible matter around us. Whatever we and where we did not see, created by fermions. Fermions are divided by quark, well interacting and locked in more complex particles like hadrons, and leptonsthat exist freely in space regardless of their fellow.

Quark They are divided into two groups.

• Top-type. By the Quarts of the Upper Type, with charge +23, belongs: upper, enchanted and true quarks
• Bottom type. By the quarks of the bottom type, with charge -13, belong: bottom, strange and adorable quarks

True and adorable are the largest quarks, and the upper and lower - the most small. Why quarks gave such unusual names, and speaking more correctly, "flavors", so far for scientists the subject of disputes.

Leptons Also divided into two groups.

• The first group, with the charge "-1", belong to it: electron, muon (more severe particle) and tau particle (the most massive)
• The second group, with a neutral charge, contains: electronic neutrino, muon neutrino and tau-neutrino

Neutrinos - there is a small particle of a substance, which is almost impossible to leave. Its charge is always equal to 0.

The question arises, will not find physicists a few more generations of particles that will be even more massive compared with the previous ones. It is difficult to answer it, but theorists believe that the generations of leptons and quarks are exhausted by three.

Do not find any similarity? And quarks, and leptons are divided into two groups, which differ from each other by charge per unit? But about this later ...

Bosons

Without them, Fermions would fly through the universe with a solid stream. But exchanging bosons, Fermions inform each other any kind of interaction. The bosons themselves do not interact with each other.

The interaction transmitted by the bosons is:

• Electromagnetic, particles - photons. With these massless particles, light is transmitted.
• Strong nuclear, particles - gluons. With their help, quark from the nucleus of the atom does not disintegrate into separate particles.
• Weak nuclear, particles - w and z bosons. With their help, fermions are echoed by weight, energy, and can turn into each other.
• Gravitational , particles - gravitons. Extremely weak in the scale of the microworld force. It becomes visible only on supermassive bodies.

A reservation about gravitational interaction.
The existence of gravitons is experimentally confirmed. They exist only in the form of the theoretical version. In the standard model, in most cases they are not considered.

That's all, the standard model is collected.

Problems just started

Despite the very beautiful representation of the particles in the scheme, two questions remained. From where the particles take their mass and what is Higgs bosonwhich is distinguished from other bosons.

In order to understand the idea of \u200b\u200busing the Higgs boson, we need to refer to the quantum field theory. In simple language, it can be argued that the whole world, the whole universe, consists not from the smallest particles, and from a variety of different fields: gluon, quark, electronic, electromagnetic, etc. In all these fields, minor oscillations constantly arise. But we perceive the strongest of them as elementary particles. Yes, and this thesis is quite controversial. From the point of view of the corpuscular-wave dualism, the same micromyr object in various situations behaves like a wave, as an elementary particle, it depends only on how physics observing the process is more convenient to simulate the situation.

Field of Higgs

It turns out that there is a so-called Higgs field, the average value of which does not want to strive for zero. As a result, this field is trying to take some permanent nonzero value throughout the universe. The field is an omnipresent and constant background, as a result of strong oscillations of which boson Higgs appears.
And precisely thanks to the Higgs field, the particles are endowed with a mass.
The mass of the elementary particle depends on how much it interacts with the Higgs field, constantly fluttering inside it.
And precisely because of the Higgs boson, or rather because of its field, the standard model has so many similar groups of particles. The Higgs field forced many addition particles, such as neutrino.

RESULTS

What was told by me is the most superficial concept of the nature of the standard model and about why we need a higgs boson. Some scientists still in the depths of the soul hoped that the particle found in 2012 and similar to Boson Higgs in the tank was simply a statistical error. After all, the Higgs field violates many beautiful symmetries of nature, making calculations of physicists more confusing.
Some even believe that the standard model lives his last years due to its imperfection. But it is experimentally proven, and the standard model of elementary particles remains an active model of genius of human thought.

The standard model of elementary particles is considered to be the largest achievement of physics of the second half of the 20th century. But what lies beyond it?

The standard model (cm) of elementary particles based on the calibration symmetry is the magnificent creation of Murray Gell-Manna, Sheldon Glashow, Stephen Weinberg, Abdus Salama and the whole pleyada of brilliant scientists. See perfectly describes the interactions between quarks and leptons at distances of about 10-17 m (1% proton diameter), which can be studied at modern accelerators. However, it begins to buck at distances 10-18 m and even more so does not provide progress towards a coveted slave scale in 10-35 m.

It is believed that it is there that all fundamental interactions merge in quantum unity. For a change, see a more complete theory, which is most likely not to become the last and final. Scientists are trying to find the replacement of the standard model. Many believe that the new theory will be built by expanding the list of symmetries that form the foundation see. One of the most promising approaches to solving this task was laid not only out of connection with the problems of cm, but even before it is created.

Particles subject to Fermi Dirac Statistics (fermions with a half-heer back) and Bose Einstein (bosons with a whole spin). In the energy well, all bosons can occupy the same lower energy level, forming condensate Bose Einstein. Fermions are subject to the principle of ban on Pauli, and therefore two particles with the same quantum numbers (in particular, unidirectional spins) cannot occupy one and the same energy level.

Mix of opposites

In the late 1960s, Senior Researcher, the Jury Golfand, Senior Researcher, offered his graduate student Evgeny Lichtman to summarize the mathematical apparatus used to describe the symmetry of the four-dimensional space-time of the special theory of relativity (Minkowski space).

Likhtman found that these symmetries can be combined with internal symmetries of quantum fields with non-zero spins. At the same time, families (multiplets) are formed, combining particles with the same mass, having a whole and half-heer back (otherwise, bosons and fermions). It was both new, and incomprehensible, since those and others obey different types of quantum statistics. Bosons can accumulate in the same condition, and fermions follow the principle of Pauli, strictly forbidding even pair unions of this kind. Therefore, the emergence of boson-fermion multiplets looked like mathematical exotic, which is not related to real physics. So it was perceived in Fian. Later, in his "memories", Andrei Sakharov called the unification of bosons and fermions a great idea, but at that time it did not seem interesting to him.

Outside the standard

Where are the boundaries cm? "The standard model is consistent with almost all data obtained at high-energy accelerators. - explains the leading researcher at the Institute of Nuclear Research RAS Sergei Troitsky. - However, in its framework, the results of experiments are not fully stacked, indicating the presence of mass in two types of neutrino, and perhaps that all three. This fact means that cm needs expanding, and in which one, no one really knows. Astrophysical data indicate the incompleteness. Dark matter, and it accounts for a more fifth part of the mass of the universe, consists of heavy particles that do not fit into the see. By the way, this matter would be more accurate to be called dark, but transparent, because it not only does not radiate light, but does not absorb it. In addition, cm does not explain the almost complete absence of antimatter in the observed universe. "
There are also objections of aesthetic order. As Sergey Troitsky notes, cm arranged quite ugly. It contains 19 numerical parameters, which are determined by the experiment and, from the point of view of common sense, take very exotic values. For example, the vacuum middle field of Higgs, which bears responsibility for the mass of elementary particles, is 240 GeV. It is not clear why this parameter is 1017 times less than the parameter determining the gravitational interaction. I would like to have a more complete theory, which will provide an opportunity to determine this ratio from some general principles.
SM does not explain the huge difference between the masses of the easiest quarks, of which protons and neutrons are composed, and a mass of top-quark exceeding 170 GeV (in all other it does not differ from U-quark, which is almost 10 thousand times easier). Where do it seems like the same particles with such various masses, while it is not clear.

Likhtman in 1971 defended his thesis, and then went to the vinity and almost abandoned theorphisus. Golfand was fired from Fian to reduce states, and he could not find work for a long time. However, employees of the Ukrainian Physico-Technical Institute Dmitry Volkov and Vladimir Akulov also opened symmetry between bosons and fermions and even took advantage of it to describe neutrinos. True, no laurels of Muscovites, nor Kharkiv, did not find it. Only in 1989, Golfand and Lichtman received the USSR Academy of Sciences Award on theoretical Physics named after I.E. Tamma. In 2009, Vladimir Akulov (now he teaches physics at the Technical College of New York City University) and Dmitry Volkov (posthumously) was awarded the National Prize of Ukraine for scientific research.

Elementary particles of the standard model are divided into bosons and fermions by type of statistics. Composite particles - hadrons - can obey either Bose-Einstein statistics (such relatives are the mesons - cows, peonies), or Fermi Dirac statistics (Barione - protons, neutrons).

Birth of supersymmetry

In the West, the mixtures of boson and fermion states first appeared in an emerging theory, representing elementary particles not point objects, but by vibrations of one-dimensional quantum strings.

In 1971, a model was built in which each vibration of boson type was combined with a pair of fermion vibration. True, this model did not work in the four-dimensional space of Minkowski, but in the two-dimensional space-time of string theories. However, already in 1973, Austrian Julius Vesz and Italian Bruno's Zumino reported to CERN (and a year later published an article) about a four-dimensional suymmetric model with one boson and one fermion. She did not claim for elementary particles, but demonstrated the possibilities of supersymmetry on a visual and extremely physical example. Soon the same scientists have proven that the symmetry detected by them is an extended version of the symmetry of Golfand and Lichtman. So it turned out that for three years the supersymmetry in the space of Minkowski independently of each other opened three pairs of physicists.

The results of Vesse and Zumino pushed the development of theories with boson-fermion mixtures. Since these theories bind calibration symmetries with symmetries of space-time, they were called supercalibration, and then supersymmetric. They predict the existence of a set of particles, none of which is not yet open. So the supersymmetry of the real world is still hypothetical. But even if it exists, it cannot be strict, otherwise the electrons would have charged bosonic rations with exactly the same mass that could be found easily. It remains to assume that the supersymmetric partners of the known particles are extremely massive, and this is possible only when the supersymmetry is violated.

SuperSymmetric ideology entered into force in the mid-1970s, when the standard model already existed. Naturally, physicists began to build its supersymmetric expansions, in other words, to introduce symmetry between bosons and fermions. The first realistic version of the supersymmetric cm, called the minimum (Minimal SuperSymmetric Standard Model, MSSM), was proposed by Howard Georgie and Savas Dimopoulos in 1981. In fact, this is the same standard model with all its symmetries, but a partner added to each particle, whose spin differs from its back to ½, - Boson to Fermion and Fermion to Boson.

Therefore, all interactions cm remain in place, but are enriched with the interactions of new particles with old and each other. Later there were more complex supersymmetric versions for see. All of them compare the already known particles of the same partners, but in different ways explain the violations of supersymmetry.

Particles and superchasts

The names of the Fermion Supporters are built using the Celectron Celectron, Chumong. Superparters bosons are seized by the end of "IO": photon - Fotinos, gluon - gluin, Z-Boson - Zino, W-Boson - Wine, Boson Higgs - Higgsino.

The spin of the superparter of any particle (with the exception of the Higgs boson) is always ½ less than its own spin. Consequently, the partners of the electron, quarks and other fermions (as well as naturally, and their anti-particles) have zero spin, and the partners of the photon and vector bosons with a single back - half. This is due to the fact that the number of particle states is the greater, the more its spin. Therefore, the replacement of subtraction to addition would lead to the appearance of excess superpartners.

Left is a standard model (cm) of elementary particles: fermions (quarks, leptons) and bosons (interaction carriers). On the right - their superpartners in the minimum supersymmetric standard model, MSSM: bosons (wipers, sandtones) and fermions (superparter interaction porter). Five higgs bosons (in the scheme are marked with one blue symbol) also have their superpart mainers - the top five Higgsino.

Take an electron for example. It may be in two states - in one spin it is directed parallel to the impulse, in the other - antipherally. From the point of view, see these different particles, since they are not quite equally involved in weak interactions. A particle with a single spin and a nonzero mass can be in three different states (as physicists say, has three degrees of freedom) and therefore is not suitable for electron's partners. The only output will be attributed to each of the states of the electron one by one superparter with zero spin and consider these selectors with various particles.

Superparter bosons standard models arise several cunning. Since the mass of the photon is zero, then it has not three, but two degrees of freedom. Therefore, it is compared to him without problems, a superparter with half spin, which, like an electron, has two degrees of freedom. In the same scheme, gluino occurs. With Higgs, the situation is more complicated. In MSSM, there are two doubles of Higgs bosons, which corresponds to the Four of SuperPartnerners - two neutral and two differently charged Higgsino. Neutrals are mixed in different ways with Fotinos and zino and form the four physically observed particles with a general name neutralino. Similar mixes with strange for Russian ear named Chardzhino (in English - Chargino) form superparters of positive and negative W-bosons and pairs of charged higgles.

The situation with superpartines neutrino has its own specifics. If this particle had no mass, its spin would always be directed opposite to the impulse. Therefore, mass-masted neutrinos could be expected to have a single scalar partner. However, real neutrinos are still not massless. It is possible that there are also neutrinos with parallel pulses and spins, but they are very difficult and not yet found. If this is true, then each variety of neutrinos corresponds to its superpartner.

As Professor of Physics of Michigan University Gordon Kane says, the most universal mechanism of impaired supersymmetry is associated with.

However, the magnitude of its contribution to the mass of superchasts is not yet clarified, but evaluations of theorists are contradictory. In addition, he is unlikely to be the only one. Thus, Next-to-Minimal SuperSymmetric Standard Model, NMSSM, introduces two more Higgs bosons that contribute to the mass of superchasts (and also increases the number of neutralino from four to five). Such a situation, Kane notes, sharply multiplies the number of parameters laid in supersymmetric theories.

Even the minimum expansion of the standard model requires about a hundred additional parameters. This is not surprised, since all these theories are introduced many new particles. As more complete and agreed models appear, the number of parameters should decrease. As soon as the detectors of a large hadron collider catch superchasts, the new models will not make themselves waiting.

Hierarchy of particles

SuperSymmetric theories allow you to eliminate a number of weak places of the standard model. Professor Kane marks a riddle associated with Higgs Boson, which is called the problem of the hierarchy.

This particle acquires a mass in the course of interaction with lepton and quarks (just as they themselves acquire the masses when interacting with the Higgs field). In cm deposits from these particles are represented by diverging rows with infinite sums. True, the contributions of bosons and fermions have different signs and in principle can almost fully pay each other. However, such a repayment should be practically ideal, since the Higgs mass, as is now known, only 125 GeV is equal. It is not impossible, but extremely unlikely.

For supersymmetric theories, there is nothing terrible. With an accurate supersymmetry, the contributions of conventional particles and their superpartiners must completely compensate each other. Since the supersymmetry is broken, compensation turns out to be incomplete, and the Higgs boson acquires the final and, most importantly calculated mass. If the masses of superpartner are not too high, it should be measured by one or two hundred GeVs, which corresponds to reality. As Kane emphasizes, physicists have become serious about the supersymmetry precisely when it was shown that it solves the problem of the hierarchy.

There are no supersymmetry capabilities on this. From cm implies that in the region of very high energies, severe, weak and electromagnetic interactions, although they have about the same force, but never combine. And in the supersymmetric models at energies of about 1016 GeV, such a union takes place, and it looks much natural. These models also offer to solve the problem of dark matter. Superchasts during decays generate both superchasts and ordinary particles - naturally, less mass. However, supersymmetry, unlike cm, allows a quick decay of the proton, which, on our happiness, does not really happen.

Proton, and with it and the entire world around us can save, suggesting that in processes with the participation of superchasts, a quantum number of R-parity is preserved, which is equal to one for conventional particles, and for superpart mainers - minus one. In this case, the easiest superchast should be fully stable (and electrically neutral). It cannot be filled with superchasts by definition, and the preservation of R-parity prohibits it to decay on particles. Dark matter may consist of precisely from such particles that have arisen immediately following the large explosion and avoiding mutual annihilation.

Waiting for experiments

"Shortly before the opening of the Higgs boson on the basis of the M-theory (the most advanced version of the string theory), its mass was predicted with a mistake of only two percent! - says Professor Kane. - The masses of selectrons, orphans and dvars were also calculated, which were too large for modern accelerators - about several tens of TEV. Superparters photon, gluons and other calibration bosons are much easier, and therefore there are chances of finding them on the tank. "

Of course, the correctness of these calculations is not guaranteed: M-theory is a delicate matter. And yet, is it possible to detect the tracks of superchasts on accelerators? "Massive superchasts should decay immediately after birth. These decays occur against the background of the decays of conventional particles, and to unambiguously allocate them very difficult, "explains the chief scientific officer of the Laboratory of Theoretical Physics of JINR in Dubna Dmitry Cossacks. - It would be perfect if the Super Spearmen showed itself a unique way, which is impossible to confuse anything else, but the theory does not predict.

It is necessary to analyze many different processes and look for those that are not fully explained by the standard model. These searches have not yet been crowned with success, but we already have restrictions on the masses of superpartines. Those of them who participate in strong interactions should pull at least 1 TEV, while the masses of other Supercarticles can vary between dozens and hundreds of GeV.

In November 2012, at the Symposium in Kyoto, the results of experiments on the tank were reported, during which a very rare breakdown of BS-meson on Muon and Antimuon was fully registered for the first time. Its probability is approximately three billion, which is well complied with predictions, see Since the expected probability of this decay, calculated on the basis of MSSM, can be several times more, someone decided that with the supersymmetry end.

However, this probability depends on several unknown parameters, which can be given both large and small contributions to the end result, there is still much unclear. Therefore, nothing terrible happened, and rumors about the death of MSSM are greatly exaggerated. But it does not even follow from this that it is invulnerable. The tank does not work at full capacity, it will be released on it only in two years, when the power of the protons will bring up to 14 TEV. And now if there are no manifestations of superchasts, then MSSM is likely to die with a natural death and the time of new suymmetric models will come.

Numbersman and supergravity

Even before creating MSSM, the suymmetry was combined with gravity. The repeated use of transformations connecting bosons and fermions moves a particle in space-time. This allows you to associate supersymmetry and deformation of the spatial-temporal metric, which, according to the general theory of relativity, is the cause of gravity. When physicists understood this, they began to build supersymmetric generalizations from the supervitations. This area of \u200b\u200btheoretical physics is actively developing now.
At the same time, it turned out that the supersymmetric theories are needed exotic numbers invented in the XIX century by the German mathematician German Gunter Grassman. They can be folded and deducted as ordinary, but the product of such numbers changes the sign when permuting the factors (therefore, the square and in general, any whole degree of grassmann number is zero). Naturally, the functions from such numbers cannot be differentiated and integrated according to the standard rules of mathematical analysis, completely different techniques are needed. And they, fortunately for supersymmetric theories, were already found. They came up in the 1960s outstanding Soviet mathematician from MSU Felix Berezin, who created a new direction - supermaatics.

However, there is another strategy that is not associated with the tank. So far, the LEP electron-positron collider worked at CERN, it was looking for the easiest of charged superchasts, whose decays should generate better superpartines. These predecessor particles are easier to register, because they are charged, and the lightest superpartner neutral. Lep experiments showed that the mass of such particles does not exceed 104 GeV. It's not so much, but they are difficult to detect on the tank because of the high background. Therefore, the construction movement has now begun to search for a super-power electron-positron collider. But this is a very expensive car, in a short time it will certainly not build. "

Closure and opening

However, according to Professor of theoretical physics of the University of Minnesota, Mikhail Shifman, the measured mass of the Higgs boson is too large for MSSM, and this model is most likely already closed:

"True, she is trying to save them with the help of various add-ons, but they are so unimpressible that they have small chances of success. It is possible that other extensions will work, but when and as is still unknown. But this question goes beyond pure science. The current financing of high-energy physics keeps at the hope of finding something really new on the tank. If this does not happen, financing will be cut, and money is not enough to build accelerators of a new generation, without which this science will not be able to develop. " So supersymmetric theories still give hopes, but the verdict of the experimenters will not wait.