Elementary particles

Back in 1950, the Italian physicist Enrico Fermi spoke on the nine elementary particles known by then that "this is already a sufficiently large number to cause suspicion of the elementality of even some of them". And in the experiments there appeared more and more elementary particles. Why did nature need so many "simplest bricks" of matter and how to organize this set, bring it into the system?..

True, elementary particles still have something in common: almost all of them interact with each other with the help of nuclear forces and form a huge class of hadrons

True, elementary particles still have something in common: almost all of them interact with each other with the help of nuclear forces and form a huge class of hadrons. Here came the protons and neutrons - the basic elementary particles, of which the core is composed. Here we received a residence permit and a family of mesons: at first it consisted of π and K-mesons, particles that are inferior in mass to protons and neutrons. But the biggest addition to the class of hadrons was made by such elementary particles as hyperons - close relatives of the proton and neutron, which differ from them in an unprecedented short lifetime. All these numerous lambda, sigma, xi, and omega hyperons are produced in collisions of nucleons with nuclei and with each other, they live trillions of a second and die, decaying again into nucleons and mesons. All elementary particles can be divided into two groups: mesons and baryons (nucleons and hyperons).

It turned out that the elementary particles protons and neutrons in the nucleus continuously exchange π-mesons, transferring them to each other. Thus an invisible link arises between them, called the exchange forces. These forces also hold together the nucleons that form the nucleus. But, what to do with the other hadrons, which only do, that they collide with each other, turning again into each other?! What is their role in the microcosm and how to distinguish elementary particles from compound, complex ones in this cluster?

Take, for example, a neutron. In the free state outside the nucleus, it decays into a proton, an electron, and a neutrino. Hence, a neutron is a complex particle. But a proton, if struck on it in an accelerator by another proton, can emit a p-meson and turn into a neutron. It turns out that now the proton is composed of a neutron and a meson? Here also understand, that here simple, elementary, and that difficult!

It turns out that all hadrons are non-elementary, which means they simply have to be composed of some parts. But what kind?

The American physicist G. Gell-Mann suggested that all known elementary hadron particles consist of different combinations of three indivisible particles, which he called "quarks". All baryons, in his opinion, should consist of three quarks, mesons - of two, a quark and an antiquark. For all observed particles, the electric charge is equal to the whole number of electron charges, so quarks should have a fractional charge in order to give the whole in sum.

The proton, for example, on this hypothesis consists of two u -quarks and one d -quark. The electric charge attributed to the u -quark is +2/3, d -quark -1/3. It is easy to verify that the charges of two u -quarks and one d -quark in the sum will give +1.

Antiquarks are designated by the same symbols as quarks, but with a dash on top, and have opposite properties. u -antikvark has a charge of -2/3, d -antiquark - +1/3. π+ -meson, for example, is constructed from the u -quark and d -antikvarka, and its charge, as expected, is + 2/3 + 1/3 = +1.

The quark model successfully explains the results of the experiments, and predicts new elementary particles.

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