Definition: Elementary particles
call a large group
the smallest particles of matter, not
being atoms or atomic
cores.
Elementary particles:
electrons
protons
neutrino
neutrons
muons
mesons
strange particles
resonances
"beautiful"
particles
photons
"enchanted" particles

Designation, mass, charge

Particle
Electron
Symbol
0e
-1
Weight, kg
Charge, Cl
9*10-31
-1,6*10-19
Proton
1p
1
1,673*10-27
+1,6*10-19
Neutron
1n
0
1,675*10-27
0
Photon
γ
0
0

The overwhelming number of elementary
particles are not found in nature, because
they are not stable, they are received in
laboratories. The main way to
getting collision fast
stable particles in progress
of which part of the kinetic energy
moving particles turns into
energy of the resulting particles
All particle transformation processes
obey the laws of conservation (energy,
impulse, charge and a number of other quantities,
specific for elementary particles).

Convertibility
elementary particles – one of
the most important properties.
Modern physics
elementary particles
also called
HIGH PHYSICS
ENERGY.

American physicists M. Gell-Mann and
G. Zweig proposed a hypothesis, according to
of which a proton consists of three
charges: -e/3, +2e/3, +2e/3. Particles with
fractional charge was called quarks.
Neutrons, according to this hypothesis,
also consists of three quarks,
having charges: -e/3, -e/3, +2e/3. So,
elementary particles are not
structureless formations.
According to the ideas of modern
physicists, protons, neutrons and others
The particles are formed from quarks, which are
have fractional electric
charges.

Antiparticles

Particles with a mass equal to the mass of an electron, but
having a positive charge. She was named
positron (0e1).
Research has shown that a positron can
appear as a result of the interaction of a γ-quantum with
heavy nucleus, and always together with an electron:
γ + X → X + 0е-1 + 0е1
Consequently, the birth of an electron–positron
pair represents the transformation of one
particle - photon (γ-quantum) into two other particles -
electron and positron.

An electron-positron pair can be generated
only a photon whose energy is not less
sum of rest energies of electron and positron:
hν ≥ 2mc2
Since the rest energy of the electron is
approximately 0.5 MeV, then the minimum energy
photon is 1 MeV, and its maximum wavelength is:
λmax = hс/2moc2=10-12 m=10-3 nm.
In a vacuum, a positron, like an electron, is stable,
stable particle. But when meeting each other
friend, the electron and positron ANNIHILATE,
generating high energy photons: 0е-1+0е1→2γ
During the annihilation of matter and antimatter
colossal energy is released -
rest energy.

Subsequently they opened
ANTI-PARTICLES of other elementary particles.
Usually the antiparticle is denoted by the same letter,
like a particle, but a wavy one is placed above it
trait. For example, a proton is denoted
the letter p, and the antiproton – p.

Fundamental Interactions
Strong
interaction
Electromagnetic
interaction
Gravitational
interaction
Weak
interaction

Strong interaction is characteristic of heavy
particles. It is this that determines the connection of protons, and
neutrons in the nuclei of atoms.
In electromagnetic interaction
electrically charged particles and photons are involved.
Due to electromagnetic interaction there is
connection of electrons with nuclei in atoms and connection of atoms in
molecules. Electromagnetic interaction
determines many macroscopic properties
substances.
Weak interaction is common to everyone
particles other than photons. His most famous
manifestation - beta decay of neutrons and atomic nuclei.
Gravitational interaction is inherent in everything
bodies of the Universe; it manifests itself in the form of forces of the universal
gravity. These forces ensure the existence of stars,
planetary systems, etc. In the microcosm gravitational
interaction is extremely weak due to the fact that
the masses of elementary particles are extremely small.

Type
interactions
Strong
Radius
actions, m
Intensity,
Vectors
relative units interactions
10-15
1
Gluons
∞
10-2
Photons
10-18
10-10
Intermediate
new
bosons
∞
10-38
Gravitons
Electromagnetic
Weak
Gravitational

Elementary particles
Leptons
Hadrons
Hadrons (from the Greek – adros large,
strong.) – protons, neutrons and
other particles participate in all
four interactions.
Leptons (from the Greek – leptos –
lightest, smallest) – electrons,
muons and other particles in three types
interaction, except
strong.

?
Are there truly
elementary particles - primary,
further indecomposable particles, from
which are supposed to consist
matter?
Truly
elementary
particles
Leptons
Vectors
interactions
Quarks

History of the discovery of elementary particles

The first elementary particle –
electron - was discovered by English
physicist J. Thomson in 1897
English physicist E. Rutherford in 1919
Found among particles knocked out of
atomic nuclei, protons. Another particle
part of the nucleus, neutron -
was opened in 1932 by English
physicist J. Chadwick.

Swiss physicist W. Pauli in 1930 For the first time
suggested that there are special elementary
particles - neutrino (Diminutive of neutron),
having no charge and (possibly) mass.
The distinctive feature of neutrinos is their enormous
penetrating ability, which makes it difficult
detection. In 1934, E. Fermi, based on
neutrino hypothesis, built the theory of β - decay.
Neutrinos were discovered experimentally in 1953.
American physicists F. Reines and K. Cowan.
The positron, the first antiparticle, was discovered
K. Andersen in 1932
In 1936, K. Anderson and S. Neddermayer (USA) under
research cosmic rays discovered
muons having an electric charge (both
signs) - particles with a mass equal to approximately 200
electron masses, but otherwise - close in
properties of the electron (and positron).

In 1947, a group of English physicists under
S. Powell's leadership in cosmic radiation
mesons were discovered (From the Greek Meson - average,
intermediate.).
In the 1960s was discovered large number particles,
extremely unstable, having extremely little
lifetime (about 10-24 - 10-23s). These particles
called resonances, make up
most of the elementary particles.
In 1976-1977 in electron annihilation experiments
and the positron, “charmed” particles were discovered.
Their existence was predicted by quark
hypothesis of the structure of elementary particles.
In 1983, intermediates were first discovered
bosons are a group of heavy particles that are
carriers of weak interaction. Opening
new elementary particles continues through
present day.

CONCLUSION:

“And it’s a miracle that despite
amazing complexity
world we can discover
in his appearances there is some
pattern."
E. Schrödinger

Presentation
completed:
Gladchenko Maria and
Gladchenko Maxim.

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Slide captions:

ELEMENTARY PARTICLES

THREE STAGES IN THE DEVELOPMENT OF ELEMENTARY PARTICLE PHYSICS When the Greek philosopher Democritus called the simplest, indivisible particles atoms (the word atom, we recall, means indivisible), then, in principle, everything probably seemed not very complicated to him. Various objects, plants, animals are built from indivisible, unchanging particles. The transformations observed in the world are a simple rearrangement of atoms. Everything in the world flows, everything changes, except the atoms themselves, which remain unchanged. Stage one. From electron to positron 1897-1932. But at the end of the 19th century. was open complex structure atoms and the electron was isolated as an integral part of the atom. Already in the twentieth century, the proton and neutron were discovered - particles that make up the atomic nucleus. At first, all these particles were looked at exactly as Democritus looked at atoms: they were considered indivisible and unchangeable primary essences, the basic building blocks of the universe. (c. 470 or 460 - 360s BC) DEMOCRITUS

Stage two. From the positron to quarks 1932 - 1970. THREE STAGES IN THE DEVELOPMENT OF ELEMENTARY PARTICLE PHYSICS The situation of attractive clarity did not last long. Everything turned out to be much more complicated: as it turned out, there are no unchanging particles at all. The word elementary itself has a double meaning. On the one hand, elementary is a matter of course, the simplest. On the other hand, by elementary we mean something fundamental that lies at the basis of things (it is in this sense that subatomic particles (the particles from which atoms are made) are now called elementary). The following simple fact prevents us from considering the currently known elementary particles to be similar to the unchanging atoms of Democritus. None of the particles are immortal. Most particles now called elementary cannot survive for more than two millionths of a second, even in the absence of any external influence. Only four particles - photon, electron, proton and neutrino - could remain unchanged if each of them were alone in the whole world.

But electrons and protons have the most dangerous brothers, positrons and antiprotons, when they collide with them, these particles mutually destroy and new ones are formed. A photon emitted by a table lamp lasts no more than 10 -8 s. This is the time it takes for it to reach the page of the book and be absorbed by the paper. Only the neutrino is almost immortal due to the fact that it interacts extremely weakly with other particles. However, neutrinos also die when they collide with other particles, although such collisions are extremely rare. So, in the eternal quest to find the unchangeable in our changing world, scientists found themselves not on a “granite foundation”, but on “shifting sand.” All elementary particles transform into each other, and these mutual transformations are the main fact of their existence.

The idea of ​​the immutability of elementary particles turned out to be untenable. But the idea of ​​their indecomposability remained. Elementary particles are no longer indivisible, but they are inexhaustible in their properties. When ultra-high energy particles collide, the particles do not break up into something that could be called their constituent parts. No, they give birth to new particles from among those that already appear in the list of elementary particles. The greater the energy of colliding particles, the greater the number, and, moreover, heavier, particles are born. This is possible due to the fact that as the speed increases, the mass of the particles increases. From just one pair of any particles with increased mass, it is possible, in principle, to obtain all currently known particles. The result of a collision of a carbon nucleus, which had an energy of 60 billion eV (thick upper line), with a silver nucleus of a photographic emulsion. The core splits into fragments that fly in different directions. At the same time, many new elementary particles - pions - are born. Similar reactions in collisions of relativistic nuclei produced in an accelerator were carried out for the first time in the world in 1976 at the High Energy Laboratory of the Joint Nuclear Research Institute in Dubna under the leadership of Academician A. M. Baldin.

Of course, in collisions of particles with energy that is not yet available, some new unknown particles will also be born. But this will not change the essence of the matter. New particles born during collisions cannot in any way be considered as components of “parent” particles; After all, “daughter” particles, if accelerated, can, without changing their nature, but only by increasing their mass, in turn, during collisions, give birth to several particles exactly the same as their “parents”, and even many other particles. According to modern concepts, elementary particles are the primary, indecomposable particles from which all matter is built. However, the indivisibility of elementary particles does not mean that they lack an internal structure.

Stage three. From the quark hypothesis to the present day. THREE STAGES IN THE DEVELOPMENT OF ELEMENTARY PARTICLE PHYSICS 1964 - ... In the 60s. doubts arose that all particles now called elementary fully justify their name. Some of them, perhaps even most of them, bear this name hardly deservedly. The reason for doubt is simple: there are a lot of these particles.

The discovery of a new elementary particle has always been and still is an outstanding triumph of science. But quite a long time ago, a share of anxiety began to be mixed with each successive triumph. Triumphs began to follow literally one after another. A group of so-called “strange” particles was discovered: K-mesons and hyperons with masses exceeding the mass of nucleons. In the 70s a large group of “charmed” particles with even larger masses was added to them. Extremely short-lived particles with a lifetime of the order of 10 -22 -10 -23 s were discovered. These particles were called resonances, and their number exceeded two hundred. In 1964, M. Gell-Mann and J. Zweig proposed a model according to which all particles participating in strong (nuclear) interactions are built from more fundamental (or primary) particles - quarks. At present, almost no one doubts the reality of quarks, although they have not been discovered in a free state.

DISCOVERY OF THE POSITRON. ANTI-PARTICLES The existence of the electron's twin - the positron - was theoretically predicted by the English physicist P. Dirac in 1931. Paul Dirac (1902-1984) Paul Adrien Maurice Dirac - English physicist, one of the creators of quantum mechanics, foreign corresponding member of the USSR Academy of Sciences (1931). Developed quantum statistics (Fermi-Dirac statistics); the relativistic theory of electron motion (Dirac equation, 1928), which predicted the positron, as well as annihilation and pair production. Laid the foundations of quantum electrodynamics and quantum theory of gravity. Nobel Prize(1933, with Erwin Schrödinger). At the same time, Dirac predicted that when a positron meets an electron, both particles should disappear (annihilate), generating high-energy photons. The reverse process can also occur - the birth of an electron-positron pair - for example, when a photon of sufficiently high energy collides (its mass must be greater than the sum of the rest masses of the particles being born) with a nucleus.

1932 The positron was discovered using a cloud chamber placed in a magnetic field. The direction of curvature of the particle track was indicated by the sign of its charge, and the ratio of its charge to mass was determined from the radius of curvature and energy of the particle. It turned out to be the same in modulus as that of the electron. The first photograph to prove the existence of the positron. The particle moved from bottom to top and, having passed the lead plate, lost part of its energy. Because of this, the curvature of the trajectory increased.

The process of creation of an electron-positron pair by a ɣ-quantum in a lead plate. In a cloud chamber located in a magnetic field, the couple leaves a characteristic trace in the form of a two-horned fork. The fact that the disappearance (annihilation) of some particles and the appearance of others during reactions between elementary particles is precisely a transformation, and not just the emergence of a new combination of constituent parts of old particles, is especially clearly revealed precisely during the annihilation of an electron-positron pair. Both of these particles have a certain mass at rest and electric charges. The photons that are born in this case have no charges and do not have rest mass, since they cannot exist at rest.

At one time, the discovery of the birth and annihilation of electron-positron pairs caused a real sensation in science. Until then, no one had imagined that the electron, the oldest of particles, the most important building material of atoms, might not be eternal. Subsequently, twins (antiparticles) were found in all particles. Antiparticles are opposed to particles precisely because when any particle meets the corresponding antiparticle, their annihilation occurs, i.e., both particles disappear, turning into radiation quanta or other particles. The antiproton and antineutron were discovered relatively recently. The electric charge of the antiproton is negative.

Atoms whose nuclei consist of antinucleons and the shell of positrons form antimatter. Antihydrogen was obtained experimentally. In 1995, for the first time, it was possible to obtain antihydrogen atoms, consisting of an antiproton and a positron, but they quickly annihilated, which made it impossible to study their properties. Now, nuclear scientists have managed to assemble a setup that creates a complex magnetic field, which makes it possible to retain previously elusive atoms. And although the time for which antihydrogen was recorded was only one tenth of a second, according to scientists, this is enough to take spectra and conduct a detailed study of the particles. CERN physicists from the ALPHA collaboration managed to keep antimatter particles from annihilation for 1000 seconds. The antihydrogen with which the scientists worked was obtained from several tens of millions of antiprotons and positrons, the source for which was the sodium isotope 22 Na. This was followed by multi-stage cleaning. After this, several thousand antimatter atoms fell into a magnetic trap.

When antimatter annihilates with matter, the rest energy turns into kinetic energy generated gamma rays. Rest energy is the largest and most concentrated reservoir of energy in the Universe. And only during annihilation is it completely released, turning into other types of energy. Therefore, antimatter is the most perfect source of energy, the most high-calorie “fuel”. It is difficult to say now whether humanity will ever be able to use this “fuel”.

NEUTRON DECAY. DISCOVERY OF NEUTRIO Nature of β-decay After the electron leaves the nucleus, the charge of the nucleus, and therefore the number of protons, increases by one. The mass number of the nucleus does not change. This means that the number of neutrons decreases by one. Consequently, inside β-radioactive nuclei, a neutron is capable of decaying into a proton and an electron. The proton remains in the nucleus, and the electron flies out. Only in stable nuclei are neutrons stable. During beta decay, an electron is emitted from the nucleus. But there is no electron in the nucleus. Where does it come from? But here's what's strange. Absolutely identical nuclei emit electrons of different energies. The newly formed nuclei, however, are exactly the same no matter what the energy of the emitted electron is. This contradicts the law of conservation of energy - the most fundamental physical law! The energy of the initial nucleus turns out to be unequal to the sum of the energies of the final nucleus and electron!!!

Pauli hypothesis The Swiss physicist W. Pauli suggested that, together with a proton and an electron, during the decay of a neutron, some kind of “invisible” particle is born, which carries away the missing energy. This particle is not detected by instruments because it does not carry an electrical charge and has no rest mass. This means that it is not capable of ionizing atoms or splitting nuclei, i.e., it cannot cause effects by which one can judge the appearance of a particle. Pauli suggested that the hypothetical particle simply interacted very weakly with matter and could therefore pass through a large thickness of matter without being detected.

Fermi called this particle neutrino, which means “neutron.” The rest mass of the neutrino, as Pauli predicted, turned out to be zero. Behind these words lies a simple meaning: there are no neutrinos at rest. Having barely had time to be born, the neutrino immediately moves at a speed of 300,000 km/s. We calculated how neutrinos interact with matter in a layer of a certain thickness. The result turned out to be far from reassuring in terms of the possibility of detecting this particle experimentally. A neutrino can travel a distance in lead equal to the distance traveled by light in a vacuum in several years.

FREE NEUTRON DECAY The role of neutrinos is not limited to explaining the β-decay of nuclei. Many elementary particles in a free state spontaneously decay with the emission of neutrinos. This is exactly how a neutron behaves. Only in nuclei does a neutron acquire stability due to interaction with other nucleons. A free neutron lives on average 16 minutes. This was experimentally proven only after nuclear reactors were built that produced powerful beams of neutrons. A neutrino (symbol ν) has an antiparticle called an antineutrino (symbol ν with a bar). When a neutron decays into a proton and an electron, it is the antineutrino that is emitted: The energy of the neutron is always greater than the sum of the energies of the proton and electron. Excess energy is carried away from the antineutrino.

Experimental discovery of neutrinos Despite its elusiveness, neutrinos (more precisely, antineutrinos), after almost 26 years of their “ghost existence” in scientific journals, were discovered experimentally. The theory predicted that when an antineutrino hits a proton, a positron and a neutron will appear: + The probability of such a process is low due to the monstrous penetrating ability of the antineutrino. But if there are a lot of antineutrinos, then we can hope to detect them.

Baksan Neutrino Station In the Baksan gorge in the Caucasus, a two-kilometer tunnel was made in a monolithic rock and a scientific laboratory was built, protected from cosmic rays by a rock several kilometers thick. The laboratory houses equipment for recording solar neutrinos and neutrinos from space.

INTERMEDIATE BOSONS - CARRIERS OF WEAK INTERACTIONS The decay of a neutron into a proton, electron and antineutrino cannot be caused nuclear forces, since the electron does not experience strong interactions and therefore cannot be created due to them. The birth of electrons is possible under the influence of electromagnetic forces. But there is also an antineutrino, which is devoid of electric charge and does not participate in electromagnetic interactions. The same situation arises during the decay of π-mesons and other particles with the emission of neutrinos or antineutrinos. Therefore, there must be some other interactions responsible for the decay of the neutron (and many other particles). This is actually true. There is a fourth type of force in nature - weak interactions. It is these forces that are the main protagonists in the tragedy of the death of particles.

These interactions are called weak because they are really weak: about 10 14 times weaker than nuclear ones! They can always be neglected where strong or electromagnetic interactions occur. But there are many processes that can only be caused by weak interactions. Due to its small value, weak interactions do not significantly affect the movement of particles. They don't speed them up or slow them down. Weak interactions are unable to hold any particles near each other to form bound states. Nevertheless, these are forces in the same sense as electromagnetic and nuclear ones. The main thing in any interaction is the birth and destruction of particles. Namely, these functions (especially the last one) are performed by weak interactions slowly, but absolutely rigorously.

Weak interactions are not at all uncommon. On the contrary, they are extremely UNIVERSAL. All particles participate in them. All particles have a charge, or more precisely, a constant of weak interactions. But only for particles participating in other interactions, the ability to weak interactions is unimportant. Only neutrinos are incapable of any interactions other than weak ones (with the exception of ultra-weak ones - gravitational ones). The role of weak interactions in the evolution of the Universe is not at all small. If weak interactions were turned off, the Sun and other stars would go out.

“Fast” and “slow” are better than “strong” and “weak.” Weak interactions are not weak at all in the sense that they cannot do anything outstanding in the microworld. They can cause the collapse of any particle that has a rest mass, if only this is allowed by the laws of conservation. Compliance with the last condition is very important. Otherwise, neutrons in nuclei would be unstable and there would be nothing in nature except hydrogen. The effects of weak interactions occur very rarely. In this sense, they are slow rather than weak, and are like a weightlifter who can lift a huge barbell, but only very, very slowly. Strong (nuclear) interactions are the fastest interactions, and the transformations of elementary particles they cause occur very often. Electromagnetic interactions work slower than strong ones, but still immeasurably faster than weak ones. The characteristic time of weak interactions is 10 -10 s versus 10 -21 C for electromagnetic ones. However, at high energies of colliding particles on the order of one hundred billion electron volts, weak interactions cease to be weak compared to electromagnetic ones.

How weak interactions occur For a long time, it was believed that weak interactions occur between four particles at one point. In the case of neutron decay, these are the neutron itself, a proton, an electron and an antineutrino. The corresponding quantum theory of weak interactions was constructed by E. Fermi, R. Feynman and other scientists. True, based on general considerations about the unity of the forces of nature, it was suggested that weak interactions, like all others, should be carried out through some kind of “weak” field. Accordingly, there must be quanta of this field - particles - carriers of interaction. But there was no experimental evidence of this.

A new and important step in the development of the theory of weak interactions was made in the 60s. American physicists S. Weinberg, S. Glashow and Pakistani scientist A. Salam, who worked in Trieste. They put forward a bold hypothesis about the unity of weak and electromagnetic interactions. The hypothesis of Weinberg, Glashow and Salam was based on the assumption expressed earlier that weak interactions are carried out by the exchange of particles, called intermediate or vector bosons, of three types: W +, W – and Z 0. The first two particles carry a charge equal to the elementary one, and the third is neutral.

The essence of the new hypothesis is as follows: the nature of the weak and electromagnetic interactions is the same in the sense that at the deepest level their true strength is the same and intermediate bosons interact with all particles at short distances in the same way as photons with charged particles. Accordingly, at very short distances, weak interactions should manifest themselves with the same strength as electromagnetic ones. Why then do these interactions still live up to their name? Why do the processes they cause proceed much more slowly than electromagnetic processes? The radius of weak interactions is much smaller than that of electromagnetic interactions. Because of this, they seem weaker than electromagnetic ones.

Slide 1

Elementary particles

Slide 2

Introduction
Elementary particles in the precise meaning of this term are primary, further indecomposable particles, of which, by assumption, all matter consists. The concept of “Elementary particles” in modern physics expresses the idea of ​​primordial entities that determine all known properties of the material world, an idea that originated in the early stages of the development of natural science and has always played a role important role in its development.
The existence of elementary particles is a kind of postulate, and testing its validity is one of the most important tasks of physics.

Slide 3

Brief historical information
The discovery of elementary particles was a natural result of the general successes in the study of the structure of matter achieved by physics at the end of the 19th century. It was prepared by comprehensive studies of the optical spectra of atoms, the study of electrical phenomena in liquids and gases, the discovery of photoelectricity, X-rays, and natural radioactivity, which indicated the existence of a complex structure of matter.
Discovery: Electron is the carrier of negative elementary electric charge in atoms, 1897. Thomson. Protons are particles with a unit positive charge and mass, 1919. Rutherford Neutron - a mass close to the mass of a proton, but does not have a charge, 1932. Chadwick Photon - 1900 Started Planck's theory Neutrino - a particle that almost does not interact with matter, 1930 Pauli

Slide 4

From the 30s to the early 50s. The study of electron particles was closely related to the study of cosmic rays. In 1932, K. Anderson discovered a positron (e+) in cosmic rays - a particle with the mass of an electron, but with a positive electric charge. The positron was the first antiparticle discovered. In 1936, American physicists K. Anderson and S. Neddermeyer discovered, while studying cosmic rays, muons (both signs of electric charge) - particles with a mass of approximately 200 electron masses, but otherwise surprisingly close in properties to e-, e+. Late 40's - early 50's. were marked by the discovery of a large group of particles with unusual properties, called “strange”.

Slide 5

Basic properties of elementary particles. Interaction classes
All electron particles are objects of extremely small masses and sizes. Most of them have masses on the order of the proton mass, equal to 1.6 × 10-24 g (only the electron mass is noticeably smaller: 9 × 10-28 g). The experimentally determined sizes of the proton, neutron, and p-meson are equal in order of magnitude to 10-13 cm. The sizes of the electron and muon could not be determined; it is only known that they are less than 10-15 cm. The microscopic masses and sizes of electron particles form the basis quantum specificity of their behavior. The characteristic wavelengths that should be attributed to electron particles in quantum theory are of the order of magnitude close to the typical dimensions at which their interaction occurs (for example, for the p meson 1.4 × 10-13 cm). This leads to the fact that quantum laws are decisive for electron particles.

Slide 6

The most important quantum property of all electron particles is their ability to be created and destroyed (emitted and absorbed) when interacting with other particles. In this respect they are completely analogous to photons
They determine the connection of protons and neutrons in the nuclei of atoms and provide the exceptional strength of these formations, which underlies the stability of matter under terrestrial conditions.
Electromagnetic interactions, in particular, are responsible for the connection of atomic electrons with nuclei and the connection of atoms in molecules.
Weak interactions give rise to very slowly occurring processes with electrons and also cause slow decays.

Slide 7

characterized primarily by the fact that they have strong interactions, along with electromagnetic and weak
participate only in electromagnetic and weak interactions

Slide 8

Slide 9

Slide 10

Some General Problems of Particle Theory
It is not known what the total number of leptons, quarks and various vector particles is and whether there are physical principles that determine this number. The reasons for the division of particles with spin 1/2 into 2 different groups are unclear: leptons and quarks. The origin of the internal quantum numbers of leptons and quarks (L, B, 1, Y, Ch) and such characteristics of quarks and gluons as “color” are unclear. freedoms are related to internal quantum numbers What mechanism determines the masses of true E. ch. What is the reason for the presence of different classes of interactions in E. ch. with different symmetry properties

Slide 11

Conclusion
Thus, the emerging trend towards the simultaneous consideration of various classes of interactions of electron particles should most likely be logically completed by including gravitational interaction in the general scheme. It is on the basis of simultaneous consideration of all types of interactions that it is most likely to expect the creation of a future theory of electron particles.

Slide 2


Test 1. What physical systems are formed from elementary particles as a result of electromagnetic interaction? A. Electrons, protons. B. Atomic nuclei. B. Atoms, molecules of matter and antiparticles. 2. From the point of view of interaction, all particles are divided into three types: A. Mesons, photons and leptons. B. Photons, leptons and baryons. B. Photons, leptons and hadrons. 3. What is the main factor in the existence of elementary particles? A. Mutual transformation. B. Stability. B. The interaction of particles with each other. 4. What interactions determine the stability of nuclei in atoms? A. Gravitational. B. Electromagnetic. B. Nuclear. D. Weak.

Slide 3


6. The reality of the transformation of matter into an electromagnetic field: A. Confirmed by the experience of annihilation of an electron and a positron. B. Confirmed by the experiment of annihilation of an electron and a proton. 7. Reaction of transformation of matter into a field: A. e + 2γ→e+B. e + 2γ→e- B.e+ +e- =2γ. 8. What interaction is responsible for the transformation of elementary particles into each other? A. Strong interaction. B. Gravitational. B. Weak interaction D. Strong, weak, electromagnetic. Answers: B; IN; A; IN; B; A; IN; D. 5. Are there unchanging particles in nature? A. There are. B. They don’t exist.

Slide 4


1964 Gell-Mann and Zweig - hypothesis about the existence of quarks. Quarks were the name given to all supposed “real elementary particles” that make up all mesons, baryons and resonances. To form such particles, quarks had to have charges +2\3 and -1\3. We didn’t know such particles!! n +2\3 -1\3 -1\3 u d d P +2\3 +2\3 -1\3 u d u Quarks:u, d, s ,c, b, t. The same number of antiquarks According to the Pauli principle: in one system of interconnected particles there never exist at least two particles with identical parameters if these particles have half-integer spin.

Slide 5


Omega - minus - hyperon consists of three identical quarks. Violation of principle?? Are quarks identical?? They cannot be identical, therefore they differ in some unknown properties. These new properties are color charges. There are three types (color) of charge on quarks. Red, blue, yellow. Antiquarks have: anti-red, anti-blue, anti-yellow charge. Quarks with the same electric charges have different color charges and there is an attractive force between them due to color interaction. The theory that describes color interaction is chromodynamics.

Slide 6


There are no free QUARKS in nature! The strengths of color interactions increase with increasing distance from the quark. When the bond between quarks is broken, a “quark-antiquark” pair is born. Color interaction is provided by GLUONS. A combination of three colors and three anticolors gives eight different gluons. It is believed today that in nature there are 36 quarks, 8 gluons, 12 leptons and photons, a total of 57 “most elementary” particles.

Slide 7


The search for the simplest fundamental principle of matter again led to the discovery of a qualitatively new stage in the knowledge of nature. “The electron is as inexhaustible as the atom, nature is infinite...” V.I. Lenin D/Z § 87

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