Sunday, December 26, 2010

Acronym in quantum chromodynamics: CQM for constituent quark model

In physics, CQM stands for constituent quark model, which has its origin in the quark hypothesis proposed in 1964 by Murray Gell-Mann and George Zweig to account for the plethora of subatomic particles discovered in cosmic ray and accelerator experiments [1]. Constituent quark means massive quark [2]. The CQM concentrates on valence quarks, which are constituents of hadrons such as protons and neutrons. Timothy Paul Smith illustrates the application of the CQM in a highly recommended article about the properties and inner dynamics of the neutron [3].

The “complex life” inside a neutron—a “quark-sea” of quark-antiquark pairs that quickly come and go—is fully described by quantum chromodynamics (QCD). The valence quark model confines description to the “permanent quarks” of a hadron: a proton is made up of two up-quarks and one down-quark, whereas a neutron is made up of two down-quarks and one up-quark. Hence, the notation uud and udd for for the proton and neutron, respectively [3].

[1] Bill Carithers and Paul Grannis: Discovery of the Top Quark. PDF.
[2] Dmitri Diakonov:
Foundations of the Constituent Quark Model.
[3] Timothy Paul Smith: The Anatomy of a Neutron. American Scientist November-December 2010, 98 (6), pp. 478-485. Abstract.

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