Small particle of the atomic universe 5 letters. Elementary particles. What is spin
In the early 30s of the twentieth century, physics found an acceptable description of the structure of matter based on four types of elementary particles - protons, neutrons, electrons and photons. The addition of a fifth particle, the neutrino, also made it possible to explain the processes of radioactive decay. It seemed that the named elementary particles were the first building blocks of the universe.
But this apparent simplicity soon disappeared. Soon the positron was discovered. In 1936, the first meson was discovered among the products of the interaction of cosmic rays with matter. After this, it was possible to observe mesons of a different nature, as well as other unusual particles. These particles were born under the influence of cosmic rays quite rarely. However, after accelerators were built that made it possible to produce high-energy particles, more than 300 new particles were discovered.
What then is meant by the word " elementary"? “Elementary” is the logical antipode of “complex.” Elementary particles mean the primary, further indecomposable particles that make up all matter. By the forties, a number of transformations of “elementary” particles were already known. The number of particles continues to grow. Most of them are unstable Among the dozens of known microparticles, there are only a few that are stable and incapable of spontaneous transformations.Isn’t stability with respect to spontaneous transformations a sign of elementarity?
The deuterium nucleus (deuteron) consists of a proton and a neutron. As a particle, the deuteron is completely stable. At the same time, the component of the deuteron, the neutron, is radioactive, i.e. unstable. This example shows that the concepts of stability and elementaryness are not identical. In modern physics the term "Elementary particles" is usually used to name a large group of tiny particles of matter(which are not atoms or atomic nuclei).
All elementary particles have extremely small masses and sizes. Most of them have a mass on the order of the mass of a proton (only the mass of an electron is noticeably smaller 
). The microscopic sizes and masses of elementary particles determine the quantum laws of their behavior. The most important quantum property of all elementary particles is the ability to be born and destroyed (emitted and absorbed) when interacting with other particles.
There are four known types of interactions between particles, different in nature: gravitational, electromagnetic, nuclear, as well as interaction in all processes involving neutrinos. What are the characteristics of the four types of interaction listed?
The strongest is the interaction between nuclear particles ("nuclear forces"). This interaction is usually called strong. It has already been noted that nuclear forces act only at very small distances between particles: the radius of action is about 10 -13 cm.
The next largest is electromagnetic interaction. It is less than strong by two orders of magnitude. But with distance it changes more slowly, like 1/ r 2, so the radius of action of electromagnetic forces is infinite.
Next comes the interaction due to the participation of neutrinos in reactions. In order of magnitude, these interactions are 10 14 times less than strong interactions. These interactions are usually called weak. Apparently, the range of action here is the same as in the case of strong interaction.
The smallest known interaction is gravitational. It is less than the strong one by 39 orders of magnitude - 10 39 times! With distance, gravitational forces decrease as slowly as electromagnetic forces, so their range of action is also infinite.
In space, the main role belongs to gravitational interactions, because The range of action of strong and weak interactions is negligible. Electromagnetic interactions play a limited role because electric charges of opposite signs tend to form neutral systems. Gravitational forces are always attractive forces. They cannot be compensated by the force of the opposite sign; they cannot be shielded from them. Hence their dominant role in space.
The magnitude of the interaction forces also corresponds to the time required to carry out the reaction caused by this interaction. Thus, processes caused by strong interaction require time of the order of 10 -23 seconds. (a reaction occurs when high-energy particles collide). The time required to carry out the process caused by electromagnetic interaction requires ~10 -21 sec., weak interaction requires ~10 -9 sec. In reactions caused by particle interactions, gravitational forces play virtually no role.
The listed interactions are apparently of a different nature, i.e., they cannot be reduced to one another. At present, there is no way to judge whether these interactions exhaust all those existing in nature.
The class of elementary particles participating in strong interactions is called hadrons (proton, neutron, etc.). A class of particles that do not have strong interactions are called leptons. Leptons include the electron, muon, neutrino, heavy lepton and their corresponding antiparticles. Antiparticles, a collection of elementary particles that have the same masses and other physical characteristics as their “twins”, but differ from them in the sign of some interaction characteristics(for example, electric charge, magnetic moment): electron and positron, neutrino and antineutrino. According to modern concepts, neutrinos and antineutrinos differ from each other in one of the quantum characteristics - helicity, defined as the projection of the spin of a particle onto the directions of its movement (momentum). Neutrinos have a spin S oriented antiparallel to the pulse R, i.e. directions R And S form a left-handed screw and the neutrino has left-handed helicity (Fig. 6.2). For antineutrinos, these directions form a right-handed screw, i.e. antineutrinos have right-handed helicity.
When a particle and an antiparticle collide, they can be mutually destroyed - "annihilate". In Fig. Figure 6.3 depicts the process of annihilation of an electron and a positron with the appearance of two gamma rays. In this case, all known conservation laws are observed - energy, momentum, angular momentum, and the law of conservation of charges. To create an electron-positron pair, it is necessary to expend energy no less than the sum of the intrinsic energies of these particles, i.e. ~ 10 6 eV. When such a pair annihilates, this energy is released either with the radiation generated during annihilation, or is distributed among other particles.
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(6.9)
The electric charge is retained during this transformation. In the same way, it is preserved when a photon transforms into an electron-positron pair or when the same pair is born as a result of a collision of two electrons.
There is a hypothesis that all elementary particles are combinations of three basic particles called quarks, and their antiparticles. Quarks have not been discovered in a free state (despite numerous searches for them at high-energy accelerators, in cosmic rays and in the environment).
It is impossible to describe the properties and transformations of microparticles without any systematization. There is no systematization based on a strict theory.
The two main groups of elementary particles are strongly interacting ( hadrons) and weakly interacting ( leptons) particles. Hadrons are divided into mesons And baryons. Baryons are divided into nucleons And hyperons. Leptons include electrons, muons and neutrinos. Below are the values by which microparticles are classified.
1. Bulk or baryonic number A. Numerous facts observed in the process of nuclear fission and the creation of a nucleon-antinucleon pair suggest that in any process the number of nucleons remains constant. All baryons are assigned the number A= +1, to each antiparticle A= –1. The law of conservation of baryon charge is satisfied exactly in all nuclear processes. Complex particles have multiple values of the baryon number. All mesons and leptons have a baryon number of zero.
2. Electric charge q represents the number of units of electrical charge (in units of the positive charge of a proton) inherent in the particle.
3. Isotopic spin(not related to the real spin). The forces acting between nucleons in a nucleus are almost independent of the type of nucleons, i.e. nuclear interactions RR, Rn And nn are the same. This symmetry of nuclear forces leads to the conservation of a quantity called isotopic spin. Isospin is conserved in strong interactions and is not conserved in processes caused by electromagnetic and weak interactions.
4. Weirdness. To explain why some processes involving hadrons do not occur, M. Gell-Mann and K. Nishijima in 1953 proposed introducing a new quantum number, which they called strangeness. The strangeness of stable hadrons ranges from –3 to +3 (integers). The strangeness of leptons has not been determined. In strong interactions, strangeness persists.
5. Spin. Characterizes the spin angular momentum.
6. Parity. An internal property of a particle associated with its symmetry with respect to right and left. Until recently, physicists believed that there was no difference between right and left. Subsequently, it turned out that they are not equivalent for all weak interaction processes - which was one of the most surprising discoveries in physics.
In classical physics, matter and the physical field were opposed to each other as two types of matter. Matter is made up of elementary particles; it is a type of matter that has rest mass. The structure of matter is discrete, while that of the field is continuous. But quantum physics has led to the leveling of this idea. In classical physics, it is believed that particles are acted upon by force fields - gravitational and electromagnetic. Classical physics did not know any other fields. In quantum physics, behind the fields they see the true carriers of interaction - the quanta of these fields, i.e. particles. For classical fields these are gravitons and photons. When the fields are strong enough and there are a lot of quanta, we stop distinguishing them as individual particles and perceive them as a field. The carriers of strong interactions are gluons. On the other hand, any microparticle (element of matter) has a dual particle-wave nature.
Since indexes i, k, l in the structural formulas the values run through 1, 2, 3, 4, the number of mesons Mik with a given spin should be equal to 16. For baryons Bikl the maximum possible number of states for a given spin (64) is not realized, since by virtue of the Pauli principle, for a given total spin, only three-quark states are allowed that have a well-defined symmetry with respect to permutations of indices i, k, 1, namely: fully symmetric for spin 3/2 and mixed symmetry for spin 1/2. This condition is l = 0 selects 20 baryon states for spin 3/2 and 20 for spin 1/2.
A more detailed examination shows that the value of the quark composition and symmetry properties of the quark system makes it possible to determine all the basic quantum numbers of the hadron ( J, P, B, Q, I, Y, Ch), excluding mass; determining the mass requires knowledge of the dynamics of the interaction of quarks and the mass of quarks, which is not yet available.
Correctly conveying the specifics of hadrons with the lowest masses and spins at given values Y And Ch, The quark model also naturally explains the overall large number of hadrons and the predominance of resonances among them. The large number of hadrons is a reflection of their complex structure and the possibility of the existence of various excited states of quark systems. It is possible that the number of such excited states is unlimited. All excited states of quark systems are unstable with respect to rapid transitions due to strong interactions into underlying states. They form the bulk of the resonances. A small fraction of resonances also consists of quark systems with parallel spin orientations (with the exception of W -). Quark configurations with antiparallel spin orientation, related to the basic. states, form quasi-stable hadrons and a stable proton.
Excitations of quark systems occur both due to changes in the rotational motion of quarks (orbital excitations) and due to changes in their spaces. location (radial excitations). In the first case, an increase in the mass of the system is accompanied by a change in the total spin J and parity R system, in the second case the increase in mass occurs without change J P . For example, mesons with JP= 2 + are the first orbital excitation ( l = 1) mesons with J P = 1 - . The correspondence of 2 + mesons and 1 - mesons of identical quark structures is clearly seen in the example of many pairs of particles:
Mesons r" and y" are examples of radial excitations of r- and y-mesons, respectively (see.
Orbital and radial excitations generate sequences of resonances corresponding to the same initial quark structure. The lack of reliable information about the interaction of quarks does not yet allow us to make quantitative calculations of excitation spectra and draw any conclusions about the possible number of such excited states. When formulating the quark model, quarks were considered as hypothetical structural elements that open up the possibility of a very convenient description of hadrons. Subsequently, experiments were carried out that allow us to talk about quarks as real material formations inside hadrons. The first were experiments on the scattering of electrons by nucleons at very large angles. These experiments (1968), reminiscent of Rutherford's classical experiments on the scattering of alpha particles on atoms, revealed the presence of point charged formations inside the nucleon. Comparison of the data from these experiments with similar data on neutrino scattering on nucleons (1973-75) made it possible to draw a conclusion about the average squared value of the electric charge of these point formations. The result turned out to be surprisingly close to the value 1 / 2 [(2 / 3 e) 2 +(1 / 3 e) 2 ]. The study of the process of hadron production during the annihilation of an electron and a positron, which supposedly goes through the sequence of processes: ® hadrons, indicated the presence of two groups of hadrons genetically associated with each of the resulting quarks, and made it possible to determine the spin of the quarks. It turned out to be equal to 1/2. The total number of hadrons born in this process also indicates that quarks of three varieties appear in the intermediate state, i.e., quarks are three-colored.
Thus, the quantum numbers of quarks, introduced on the basis of theoretical considerations, have been confirmed in a number of experiments. Quarks are gradually acquiring the status of new electron particles. If further research confirms this conclusion, then quarks are serious contenders for the role of true electron particles for the hadronic form of matter. Up to lengths ~ 10 -15 cm quarks act as structureless point formations. The number of known types of quarks is small. In the future, it may, of course, change: one cannot guarantee that at higher energies hadrons with new quantum numbers, owing their existence to new types of quarks, will not be discovered. Detection Y-mesons confirms this point of view. But it is quite possible that the increase in the number of quarks will be small, that general principles impose limits on the total number of quarks, although these limits are not yet known. The structurelessness of quarks also perhaps reflects only the achieved level of research into these material formations. However, a number of specific features of quarks give some reason to assume that quarks are particles that complete the chain of structural components of matter.
Quarks differ from all other electron particles in that they have not yet been observed in a free state, although there is evidence of their existence in a bound state. One of the reasons for the non-observation of quarks may be their very large mass, which prevents their production at the energies of modern accelerators. It is possible, however, that quarks fundamentally, due to the specific nature of their interaction, cannot be in a free state. There are theoretical and experimental arguments in favor of the fact that the forces acting between quarks do not weaken with distance. This means that infinitely more energy is required to separate quarks from each other, or, otherwise, the emergence of quarks in a free state is impossible. The inability to isolate quarks in a free state makes them a completely new type of structural units of matter. It is unclear, for example, whether it is possible to raise the question of the constituent parts of quarks if the quarks themselves cannot be observed in a free state. It is possible that under these conditions, parts of the quarks do not physically manifest themselves at all, and therefore the quarks act as the last stage in the fragmentation of hadronic matter.
Elementary particles and quantum field theory.
To describe the properties and interactions of electron particles in modern theory, the concept of physics is essential. field, which is assigned to each particle. A field is a specific form of matter; it is described by a function specified at all points ( X)space-time and possessing certain transformation properties in relation to transformations of the Lorentz group (scalar, spinor, vector, etc.) and groups of “internal” symmetries (isotopic scalar, isotopic spinor, etc.). An electromagnetic field with the properties of a four-dimensional vector And m (x) (m = 1, 2, 3, 4) is historically the first example of a physical field. The fields that are compared with E. particles are of a quantum nature, that is, their energy and momentum are composed of many parts. portions - quanta, and the energy E k and the momentum p k of the quantum are related by the relation of the special theory of relativity: E k 2 = p k 2 c 2 + m 2 c 2 . Each such quantum is an electron particle with a given energy E k , momentum p k and mass m. The quanta of the electromagnetic field are photons, the quanta of other fields correspond to all other known electron particles. The field, therefore, is a physical reflection of the existence of an infinite collections of particles - quanta. The special mathematical apparatus of quantum field theory makes it possible to describe the birth and destruction of a particle at each point x.
The transformation properties of the field determine all quantum numbers of E. particles. The transformation properties in relation to space-time transformations (the Lorentz group) determine the spin of particles. Thus, a scalar corresponds to spin 0, a spinor - spin 1/2, a vector - spin 1, etc. The existence of such quantum numbers as L, B, 1, Y, Ch and for quarks and gluons "color" follows from the transformation properties of fields in relation to transformations of “internal spaces” (“charge space”, “isotopic space”, “unitary space”, etc.). The existence of “color” in quarks, in particular, is associated with a special “colored” unitary space. The introduction of “internal spaces” in the theoretical apparatus is still a purely formal device, which, however, can serve as an indication that the dimension of physical space-time, reflected in the properties of the E. Ch., is actually greater than four - the dimension of space-time characteristic of all macroscopic physical processes. The mass of an electron is not directly related to the transformation properties of fields; this is their additional characteristic.
To describe the processes occurring with electron particles, it is necessary to know how various physical fields are related to each other, that is, to know the dynamics of the fields. In the modern apparatus of quantum field theory, information about the dynamics of fields is contained in a special quantity expressed through fields - the Lagrangian (more precisely, the Lagrangian density) L. Knowledge of L allows, in principle, to calculate the probabilities of transitions from one set of particles to another under the influence of various interactions. These probabilities are given by the so-called. scattering matrix (W. Heisenberg, 1943), expressed through L. The Lagrangian L consists of the Lagrangian L, which describes the behavior of free fields, and the interaction Lagrangian, L, constructed from the fields of different particles and reflecting the possibility of their mutual transformations. Knowledge of Lz is decisive for describing processes with E. h.
All five letter elementary particles are listed below. A brief description is given for each definition.
If you have something to add, then below is a comment form at your service, in which you can express your opinion or add to the article.
List of elementary particles
Photon
It is a quantum of electromagnetic radiation, for example light. Light, in turn, is a phenomenon that consists of streams of light. A photon is an elementary particle. A photon has a neutral charge and zero mass. The photon spin is equal to unity. The photon carries the electromagnetic interaction between charged particles. The term photon comes from the Greek phos, meaning light.
Phonon
It is a quasiparticle, a quantum of elastic vibrations and displacements of atoms and molecules of the crystal lattice from an equilibrium position. In crystal lattices, atoms and molecules constantly interact, sharing energy with each other. In this regard, it is almost impossible to study phenomena similar to vibrations of individual atoms in them. Therefore, random vibrations of atoms are usually considered according to the type of propagation of sound waves inside a crystal lattice. The quanta of these waves are phonons. The term phonon comes from the Greek phone - sound.
Phazon
The fluctuon phason is a quasiparticle, which is an excitation in alloys or in another heterophase system, forming a potential well (ferromagnetic region) around a charged particle, say an electron, and capturing it.
Roton
It is a quasiparticle that corresponds to elementary excitation in superfluid helium, in the region of high impulses, associated with the occurrence of vortex motion in a superfluid liquid. Roton, translated from Latin means - spinning, spinning. Roton appears at temperatures greater than 0.6 K and determines exponentially temperature-dependent properties of heat capacity, such as normal density entropy and others.
Meson
It is an unstable non-elementary particle. A meson is a heavy electron in cosmic rays.
The mass of a meson is greater than the mass of an electron and less than the mass of a proton.
Mesons have an even number of quarks and antiquarks. Mesons include Pions, Kaons and other heavy mesons.
Quark
It is an elementary particle of matter, but so far only hypothetically. Quarks are usually called six particles and their antiparticles (antiquarks), which in turn make up a group of special elementary particles hadrons.
It is believed that particles that participate in strong interactions, such as protons, neurons and some others, consist of quarks tightly connected to each other. Quarks constantly exist in different combinations. There is a theory that quarks could exist in a free form in the first moments after the big bang.
Gluon
Elementary particle. According to one theory, gluons seem to glue quarks together, which in turn form particles such as protons and neurons. In general, gluons are the smallest particles that form matter.
boson
Boson-quasiparticle or Bose-particle. A boson has zero or integer spin. The name is given in honor of the physicist Shatyendranath Bose. A boson is different in that an unlimited number of them can have the same quantum state.
Hadron
A hadron is an elementary particle that is not truly elementary. Consists of quarks, antiquarks and gluons. The hadron has no color charge and participates in strong interactions, including nuclear ones. The term hadron, from the Greek adros, means large, massive.
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If strong decays were grouped in the region of yoctoseconds, electromagnetic ones - in the vicinity of attoseconds, then weak decays “followed everyone’s responsibility” - they covered as much 27 orders of magnitude on the time scale!
At the extreme ends of this unimaginably wide range are two “extreme” cases.
- Decays of the top quark and weak force carrier particles (W and Z bosons) occur in approximately 0.3 is= 3·10 −25 s. These are the fastest decays among all elementary particles and, in general, the fastest processes reliably known to modern physics. It turns out this way because these are the decays with the highest energy release.
- The longest-lived elementary particle, the neutron, lives for approximately 15 minutes. Such a huge time by the standards of the microcosm is explained by the fact that this process (the beta decay of a neutron into a proton, electron and antineutrino) has a very small energy release. This energy release is so weak that under suitable conditions (for example, inside an atomic nucleus), this decay may already be energetically unfavorable, and then the neutron becomes completely stable. Atomic nuclei, all the matter around us, and we ourselves exist only thanks to this amazing weakness of beta decay.
Between these extremes, most weak decays also occur more or less compactly. They can be divided into two groups, which we will roughly call: fast weak decays and slow weak decays.
Fast ones are decays lasting about a picosecond. So, it’s surprising how the numbers in our world have developed that the lifetimes of several dozen elementary particles fall into a narrow range of values from 0.4 to 2 ps. These are the so-called charmed and lovely hadrons - particles that contain a heavy quark.
Picoseconds are wonderful, they are simply priceless from the point of view of experiments at colliders! The fact is that in 1 ps a particle will have time to fly a third of a millimeter, and a modern detector can easily measure such large distances. Thanks to these particles, the picture of particle collisions at the collider becomes “easy to read” - here the collision and creation of a large number of hadrons occurred, and over there, a little further away, secondary decays occurred. The lifetime becomes directly measurable, which means it becomes possible to find out what kind of particle it was, and only then use this information for more complex analysis.
Slow weak decays are decays that start at hundreds of picoseconds and extend over the entire nanosecond range. This includes the class of so-called “strange particles” - numerous hadrons containing a strange quark. Despite their name, for modern experiments they are not strange at all, but on the contrary, they are the most ordinary particles. They just looked strange in the 50s of the last century, when physicists suddenly began to discover them one after another and did not quite understand their properties. By the way, it was the abundance of strange hadrons that pushed physicists half a century ago to the idea of quarks.
From the point of view of modern experiments with elementary particles, nanoseconds are a lot. This is so much that the particle ejected from the accelerator simply does not have time to disintegrate, but pierces the detector, leaving its mark in it. Of course, it will then get stuck somewhere in the material of the detector or in the rocks around it and disintegrate there. But physicists no longer care about this decay; they are only interested in the trace that this particle left inside the detector. So for modern experiments such particles look almost stable; they are therefore called the "intermediate" term - metastable particles.
Well, the longest-lived particle, not counting the neutron, is the muon - a kind of “brother” of the electron. It does not participate in strong interactions, it does not decay due to electromagnetic forces, so only weak interactions remain for it. And since it is quite light, it lives for 2 microseconds - an entire epoch on the scale of elementary particles.
In physics, elementary particles were physical objects on the scale of the atomic nucleus that cannot be divided into their component parts. However, today, scientists have managed to split some of them. The structure and properties of these tiny objects are studied by particle physics.
The smallest particles that make up all matter have been known since ancient times. However, the founders of the so-called “atomism” are considered to be the Ancient Greek philosopher Leucippus and his more famous student, Democritus. It is assumed that the latter coined the term “atom”. From the ancient Greek “atomos” is translated as “indivisible”, which determines the views of ancient philosophers.
Later it became known that the atom can still be divided into two physical objects - the nucleus and the electron. The latter subsequently became the first elementary particle, when in 1897 the Englishman Joseph Thomson conducted an experiment with cathode rays and discovered that they were a stream of identical particles with the same mass and charge.
In parallel with Thomson's work, Henri Becquerel, who studies x-rays, conducts experiments with uranium and discovers a new type of radiation. In 1898, a French pair of physicists, Marie and Pierre Curie, studied various radioactive substances, discovering the same radioactive radiation. It would later be found to consist of alpha particles (2 protons and 2 neutrons) and beta particles (electrons), and Becquerel and Curie would receive the Nobel Prize. While conducting her research with elements such as uranium, radium and polonium, Marie Sklodowska-Curie did not take any safety measures, including not even using gloves. As a result, in 1934 she was overtaken by leukemia. In memory of the achievements of the great scientist, the element discovered by the Curie couple, polonium, was named in honor of Mary’s homeland - Polonia, from Latin - Poland.
Photo from the V Solvay Congress 1927. Try to find all the scientists from this article in this photo.
Since 1905, Albert Einstein has devoted his publications to the imperfection of the wave theory of light, the postulates of which were at odds with the results of experiments. Which subsequently led the outstanding physicist to the idea of a “light quantum” - a portion of light. Later, in 1926, it was named “photon”, translated from the Greek “phos” (“light”), by the American physical chemist Gilbert N. Lewis.
In 1913, Ernest Rutherford, a British physicist, based on the results of experiments already carried out at that time, noted that the masses of the nuclei of many chemical elements are multiples of the mass of the hydrogen nucleus. Therefore, he assumed that the hydrogen nucleus is a component of the nuclei of other elements. In his experiment, Rutherford irradiated a nitrogen atom with alpha particles, which as a result emitted a certain particle, named by Ernest as a “proton”, from the other Greek “protos” (first, main). Later it was experimentally confirmed that the proton is a hydrogen nucleus.
Obviously, the proton is not the only component of the nuclei of chemical elements. This idea is led by the fact that two protons in the nucleus would repel each other, and the atom would instantly disintegrate. Therefore, Rutherford hypothesized the presence of another particle, which has a mass equal to the mass of a proton, but is uncharged. Some experiments of scientists on the interaction of radioactive and lighter elements led them to the discovery of another new radiation. In 1932, James Chadwick determined that it consists of those very neutral particles that he called neutrons.
Thus, the most famous particles were discovered: photon, electron, proton and neutron.
Further, the discovery of new subnuclear objects became an increasingly frequent event, and at the moment about 350 particles are known, which are generally considered “elementary”. Those of them that have not yet been split are considered structureless and are called “fundamental.”
What is spin?
Before moving forward with further innovations in the field of physics, the characteristics of all particles must be determined. The most well-known, apart from mass and electric charge, also includes spin. This quantity is otherwise called “intrinsic angular momentum” and is in no way related to the movement of the subnuclear object as a whole. Scientists were able to detect particles with spin 0, ½, 1, 3/2 and 2. To visualize, albeit simplified, spin as a property of an object, consider the following example.
Let an object have a spin equal to 1. Then such an object, when rotated 360 degrees, will return to its original position. On a plane, this object can be a pencil, which, after a 360-degree turn, will end up in its original position. In the case of zero spin, no matter how the object rotates, it will always look the same, for example, a single-color ball.
For a ½ spin, you will need an object that retains its appearance when rotated 180 degrees. It can be the same pencil, only sharpened symmetrically on both sides. A spin of 2 will require the shape to be maintained when rotated 720 degrees, and a spin of 3/2 will require 540.
This characteristic is very important for particle physics.
Standard Model of Particles and Interactions
Having an impressive set of micro-objects that make up the world around us, scientists decided to structure them, and this is how the well-known theoretical structure called the “Standard Model” was formed. She describes three interactions and 61 particles using 17 fundamental ones, some of which she predicted long before the discovery.
The three interactions are:
- Electromagnetic. It occurs between electrically charged particles. In a simple case, known from school, oppositely charged objects attract, and similarly charged objects repel. This happens through the so-called carrier of electromagnetic interaction - the photon.
- Strong, otherwise known as nuclear interaction. As the name implies, its action extends to objects of the order of the atomic nucleus; it is responsible for the attraction of protons, neutrons and other particles also consisting of quarks. The strong interaction is carried by gluons.
- Weak. Effective at distances a thousand smaller than the size of the core. Leptons and quarks, as well as their antiparticles, take part in this interaction. Moreover, in the case of weak interaction, they can transform into each other. The carriers are the W+, W− and Z0 bosons.
So the Standard Model was formed as follows. It includes six quarks, from which all hadrons (particles subject to strong interaction) are composed:
- Upper(u);
- Enchanted (c);
- true(t);
- Lower (d);
- Strange(s);
- Adorable (b).
It is clear that physicists have plenty of epithets. The other 6 particles are leptons. These are fundamental particles with spin ½ that do not participate in the strong interaction.
- Electron;
- Electron neutrino;
- Muon;
- Muon neutrino;
- Tau lepton;
- Tau neutrino.
And the third group of the Standard Model are gauge bosons, which have a spin equal to 1 and are represented as carriers of interactions:
- Gluon – strong;
- Photon – electromagnetic;
- Z-boson - weak;
- The W boson is weak.
These also include the recently discovered spin-0 particle, which, simply put, imparts inert mass to all other subnuclear objects.
As a result, according to the Standard Model, our world looks like this: all matter consists of 6 quarks, forming hadrons, and 6 leptons; all these particles can participate in three interactions, the carriers of which are gauge bosons.
Disadvantages of the Standard Model
However, even before the discovery of the Higgs boson, the last particle predicted by the Standard Model, scientists had gone beyond its limits. A striking example of this is the so-called. “gravitational interaction”, which is on par with others today. Presumably, its carrier is a particle with spin 2, which has no mass, and which physicists have not yet been able to detect - the “graviton”.
Moreover, the Standard Model describes 61 particles, and today more than 350 particles are already known to humanity. This means that the work of theoretical physicists is not over.
Particle classification
To make their life easier, physicists have grouped all particles depending on their structural features and other characteristics. Classification is based on the following criteria:
- Lifetime.
- Stable. These include proton and antiproton, electron and positron, photon, and graviton. The existence of stable particles is not limited by time, as long as they are in a free state, i.e. don't interact with anything.
- Unstable. All other particles after some time disintegrate into their component parts, which is why they are called unstable. For example, a muon lives only 2.2 microseconds, and a proton - 2.9 10 * 29 years, after which it can decay into a positron and a neutral pion.
- Weight.
- Massless elementary particles, of which there are only three: photon, gluon and graviton.
- Massive particles are all the rest.
- Spin meaning.
- Whole spin, incl. zero, have particles called bosons.
- Particles with half-integer spin are fermions.
- Participation in interactions.
- Hadrons (structural particles) are subnuclear objects that take part in all four types of interactions. It was mentioned earlier that they are composed of quarks. Hadrons are divided into two subtypes: mesons (integer spin, bosons) and baryons (half-integer spin, fermions).
- Fundamental (structureless particles). These include leptons, quarks and gauge bosons (read earlier - “Standard Model..”).
Having familiarized yourself with the classification of all particles, you can, for example, accurately determine some of them. So the neutron is a fermion, a hadron, or rather a baryon, and a nucleon, that is, it has a half-integer spin, consists of quarks and participates in 4 interactions. Nucleon is a common name for protons and neutrons.
- It is interesting that opponents of the atomism of Democritus, who predicted the existence of atoms, stated that any substance in the world is divided indefinitely. To some extent, they may turn out to be right, since scientists have already managed to divide the atom into a nucleus and an electron, the nucleus into a proton and a neutron, and these, in turn, into quarks.
- Democritus assumed that atoms have a clear geometric shape, and therefore the “sharp” atoms of fire burn, the rough atoms of solids are firmly held together by their protrusions, and the smooth atoms of water slip during interaction, otherwise they flow.
- Joseph Thomson compiled his own model of the atom, which he saw as a positively charged body into which electrons seemed to be “stuck.” His model was called the “Plum pudding model.”
- Quarks got their name thanks to the American physicist Murray Gell-Mann. The scientist wanted to use a word similar to the sound of a duck quack (kwork). But in James Joyce's novel Finnegans Wake he encountered the word “quark” in the line “Three quarks for Mr. Mark!”, the meaning of which is not precisely defined and it is possible that Joyce used it simply for rhyme. Murray decided to call the particles this word, since at that time only three quarks were known.
- Although photons, particles of light, are massless, near a black hole they appear to change their trajectory as they are attracted to it by gravitational forces. In fact, a supermassive body bends space-time, which is why any particles, including those without mass, change their trajectory towards the black hole (see).
- The Large Hadron Collider is “hadronic” precisely because it collides two directed beams of hadrons, particles with dimensions on the order of an atomic nucleus that participate in all interactions.
