Quark

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

Colour

Since quarks are fermions, the Pauli exclusion principle implies that the three valence quarks must be in an antisymmetric combination in a baryon. However, the charge Q =  2 baryon, ?++ (which is one of four isospin Iz  =  3/2 baryons) can only be made of three u quarks with parallel spins. Since this configuration is symmetric under interchange of the quarks, it implies that there exists another internal quantum number, which would then make the combination antisymmetric. This is given the name colour, although it has nothing to do with the physiological sensation of colour. This quantum number is the charge involved in the gauge theory called quantum chromodynamics (QCD).

Related Topics:
Pauli exclusion principle - Charge - Gauge theory - Quantum chromodynamics

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The only other coloured particle is the gluon, which is the gauge boson of QCD. Like all other non-Abelian gauge theories (and unlike quantum electrodynamics) the gauge bosons interact with one another by the same force that affects the quarks.

Related Topics:
Gluon - Quantum electrodynamics

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Colour is a gauged SU(3) symmetry. Quarks are placed in the fundamental representation, 3, and hence come in three colors. Gluons are placed in the adjoint representation, 8, and hence come in eight varieties. For more on this, see the article on color charge.

Related Topics:
SU(3) - Fundamental representation - Adjoint representation - Color charge

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