Quark

:For other uses of this term, see: Quark (disambiguation)

History

The notion of quarks evolved out of a classification of hadrons developed independently in 1961 by Murray Gell-Mann and Kazuhiko Nishijima, which nowadays goes by the name of the quark model. The scheme grouped together particles with isospin and strangeness using an unitary symmetry derived from current algebra, which we today recognise as part of the approximate chiral symmetry of QCD. This is a global flavour SU(3) symmetry, which should not be confused with the gauge symmetry of QCD.

Related Topics:
Hadron - 1961 - Murray Gell-Mann - Kazuhiko Nishijima - Quark model - Current algebra - SU(3)

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In this scheme the lightest mesons (spin-0) and baryons (spin-½) are grouped together into octets, 8, of flavour symmetry. A classification of the spin-3/2 baryons into the representation 10 yielded a prediction of a new particle, ??, the discovery of which in 1968 led to wide acceptance of the model. The missing representation 3 was identified with quarks.

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This scheme was called the eightfold way by Gell-Mann, a clever conflation of the octets of the model with the eightfold way of Buddhism. He also invented the name quark and attributed it to the sentence ?Three quarks for Muster Mark? in James Joyce's Finnegans Wake. (James Gleick's book Genius asserts that this was an after-the-fact attribution, and notes that physicists pronounced quark to rhyme with cork, not Mark.) The negative results of quark search experiments caused Gell-Mann to hold that quarks were mathematical fiction.

Related Topics:
Eightfold way - Buddhism - James Joyce - Finnegans Wake - James Gleick

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Analysis of certain properties of high energy reactions of hadrons led Richard Feynman to postulate substructures of hadrons, which he called partons (since they form part of hadrons). A scaling of deep inelastic scattering cross sections derived from current algebra by James Bjorken received an explanation in terms of partons. When Bjorken scaling was verified in an experiment in 1969, it was immediately realized that partons and quarks could be the same thing. With the proof of asymptotic freedom in QCD in 1973 by David Gross, Frank Wilczek and David Politzer the connection was firmly established.

Related Topics:
Richard Feynman - Parton - Deep inelastic scattering - James Bjorken - Bjorken scaling - 1969 - Asymptotic freedom - 1973 - David Gross - Frank Wilczek - David Politzer

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The charm quark was postulated by Sheldon Glashow, Iliopoulos and Maiani in 1973 to prevent unphysical flavour changes in weak decays which would otherwise occur in the standard model. The discovery in 1975 of the meson which came to be called the J/? led to the recognition that it was made of a charm quark and its antiquark.

Related Topics:
Sheldon Glashow - Iliopoulos - Maiani - 1973 - Standard model - 1975

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The existence of a third generation of quarks was predicted by Kobayashi and Maskawa who realized that the observed violation of CP symmetry by neutral kaons could not be accommodated into the Standard Model with two generations of quarks. The bottom quark was discovered in 1980 and the top quark in 1996 at the Tevatron collider in Fermilab.

Related Topics:
Kobayashi - Maskawa - CP symmetry - Kaon - Standard Model - 1980 - 1996 - Tevatron collider - Fermilab

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