Physics:Quantum quark
A quark is an elementary particle and a type of fermion. Quarks carry color charge and interact through the strong interaction described by quantum chromodynamics (QCD). They are constituents of composite particles such as protons, neutrons and mesons.[1][2]
Quarks are not observed as isolated free particles under ordinary conditions. In QCD, the interaction energy between separated color charges leads to confinement, so quarks appear inside hadrons or in high-energy states such as quark-gluon plasma.[3]
Overview
Quarks have spin , so they obey Fermi-Dirac statistics. Each quark also has an antiquark with opposite electric charge and opposite color charge. Quarks participate in the strong, weak and electromagnetic interactions, while neutrally charged leptons do not participate in the strong interaction.[1]
The known quark flavors are up, down, charm, strange, top and bottom. Up-type quarks have electric charge in units of the elementary charge. Down-type quarks have electric charge . Ordinary atomic nuclei are built from protons and neutrons, whose valence structure is dominated by up and down quarks.[2]
Color charge and confinement
In QCD, quarks carry color charge rather than ordinary visual color. The three color labels are conventionally called red, green and blue. Gluons mediate the strong interaction and also carry color charge, which makes QCD a non-Abelian gauge theory.[3]
Color confinement means that isolated quarks are not detected as separate particles at low energy. When a high-energy collision produces quarks, the observed final state is a set of hadrons formed by hadronization. This behavior is central to the experimental study of quarks in particle accelerators.
Hadrons
Quarks combine into color-neutral composite particles. Baryons contain three valence quarks; the proton has valence content , and the neutron has valence content . Mesons contain a quark and an antiquark. The full quantum state of a hadron also includes gluons and sea quark-antiquark pairs.
History
Murray Gell-Mann and George Zweig proposed quark-like constituents in 1964 as a way to organize the observed hadron spectrum.[4][5] Deep inelastic scattering experiments later showed that nucleons contain point-like charged constituents, which supported the quark picture.[6]
See also
Table of contents (72 articles)
Index
Full contents
References
- ↑ 1.0 1.1 Griffiths, David J. (2008). Introduction to Elementary Particles (2nd ed.). Wiley-VCH. ISBN 978-3-527-40601-2.
- ↑ 2.0 2.1 Halzen, Francis; Martin, Alan D. (1984). Quarks and Leptons: An Introductory Course in Modern Particle Physics. Wiley. ISBN 978-0-471-88741-6.
- ↑ 3.0 3.1 Peskin, Michael E.; Schroeder, Daniel V. (1995). An Introduction to Quantum Field Theory. Addison-Wesley. ISBN 978-0-201-50397-5.
- ↑ Gell-Mann, M. (1964). "A Schematic Model of Baryons and Mesons". Physics Letters 8 (3): 214-215. doi:10.1016/S0031-9163(64)92001-3. Bibcode: 1964PhL.....8..214G.
- ↑ Zweig, G. (1964). An SU(3) Model for Strong Interaction Symmetry and its Breaking (Report). CERN.
- ↑ Friedman, Jerome I. (1991). "Deep inelastic scattering: Comparisons with the quark model". Reviews of Modern Physics 63 (3): 615-629. doi:10.1103/RevModPhys.63.615. Bibcode: 1991RvMP...63..615F.
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