English-Russian translation

Date: 2015-10-07; view: 409.

TRANSLATION

1. Physicists discovered a third generation of quarks in 1977. American physicist Leon Lederman and his collaborators discovered mesons that contained a fifth quark: the bottom quark. Scientists assumed the bottom quark should have a partner, called the top quark, and so the hunt for this particle was on. This hunt finally ended in 1995, when evidence of the top quark was detected at the Fermi National Accelerator Laboratory in Batavia, Illinois. While the existence of the top quark was no surprise, the mass of it was. The top quark is over 40 times heavier than the bottom quark, and 174 times heavier than the proton, which contains three first generation quarks (two up quarks and one down quark).

2. Most of the predictions of the standard model have been verified, but physicists still seek evidence of physics beyond the standard model. They look for new particles both on Earth and throughout the cosmos. They work on theories that would explain why particles have the masses scientists have observed. In particular, they want to understand why the top quark is so much heavier than the other particles and why the second and third generation of particles exist at all. They look for connections between the four forces in the universe and continue their quest for a theory of everything.

3. Although the various particles differ widely in mass, charge, lifetime and in other ways, they all share two attributes that qualify them as being "elementary." First, as far as we know, any two particles of the same species are, except for their position and state of motion, absolutely identical, whether they occupy the same atom or lie at opposite ends of the universe. Second, there is not now any successful theory that explains the elementary particles in terms of more elementary constituents, in the sense that the atomic nucleus is understood to be composed of protons and neutrons and the atom is understood to be composed of a nucleus and electrons. It is true that the elementary particles behave in some respects as if they were composed of still more elementary constituents, named quarks, but in spite of strenuous efforts it has been impossible to break particles into quarks.

4. We have discovered that the electron has a sibling and cousins that are apparently equally fundamental. The sibling is an electrically neutral particle, called the neutrino, which is much lighter than the electron. The cousins are two electrically charged particles, called the mu and the tau, which also have neutral siblings. The mu and the tau seem to be identical copies of the electron, except that they are respectively 200 and 3,500 times heavier. Their role in the scheme of things and the origin of their different masses remain mysteries—just the sort of mysteries that particle physicists, who study the constituents of matter and the forces that control their behavior, wish to resolve.

5. The number of protons in the nucleus of an atom determines what kind of chemical element it is. All substances in nature are made up of combinations of the 92 different chemical elements, substances that cannot be broken into simpler substances by chemical processes. The atom is the smallest part of a chemical element that still retains the properties of the element. The number of protons in each atom can range from one in the hydrogen atom to 92 in the uranium atom, the heaviest naturally occurring element. (In the laboratory, scientists have created elements with as many as 114 protons in each nucleus.) The atomic number of an element is equal to the number of protons in each atom's nucleus. The number of electrons in an uncharged atom must be equal to the number of protons, and the arrangement of these electrons determines the chemical properties of the atom.

(From different sources)