Quark. In particle physics quarks are the fundamental constituents of matter along with leptons .
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- 1 History
- 2 Definition
- 3 Mass
- 4 Source
The quark concept was independently proposed in 1963 by American physicists Murray Gell-Mann and George Zweig . The term quark was taken from Finnegans Wake by the Irish writer James Joyce .
At first it was thought that there were three types of quark: up, down and strange. For example, the proton is believed to be made up of two quarks up and two quarks down. Later, theorists postulated the existence of a fourth quark; in 1974 the existence of this quark, called charm, was confirmed experimentally. Subsequently, the hypothesis of a fifth and sixth quark – called bottom and top respectively – was proposed for theoretical reasons of symmetry.
In 1977 experimental evidence was obtained of the existence of the quark bottom, but the top quark was not found by investigators until April 1994 , when physicists at the Fermi National Accelerator Laboratory (Fermilab) in the United States , announced they had found experimental evidence of its existence.
Each type of quark has its corresponding antiparticle, and there are three different classes or colors within each quark or antiquark. Quarks can be red , blue, or green , while antiquarks can be anti-red, anti-blue, or green. The colors of quarks and antiquarks have nothing to do with the colors that distinguish the human eye , but represent a quantum property. When combined to form hadrons, quarks and antiquarks can only exist in certain color groupings. The hypothetical carrier of the force between quarks is called gluon.
The quarks or quarks, along with the leptons, are the fundamental constituents of matter. Several species of quarks specifically combine to form particles such as protons and neutrons. Quarks are the only fundamental particles that interact with the four fundamental forces. Quarks are spin 1/2 particles, so they are fermions. They form visible matter alongside leptons.
Each of the six types of quark is characterized, among other things, by a mass index. The mass increases according to the number of the generation, the third being the heaviest so far. Although the mass of quarks is spoken of in the same sense as the mass of any other particle, the notion of the mass of a quark is a theoretical construction.
- Up 1.5 – 4.0 MeV
- Down 4 – 8 MeV
- Strange 80 – 130 MeV
- Charm 1150 – 1350 MeV
- Bottom 4100 – 4400 MeV
- Top 170 900 ± 1800 MeV