Charm is the number of charm quarks (c) minus the number of charm anti-quarks () that are present in a particle: For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ...
This makes charm quark to have a charm of +1 and anti-charm quark to have a charm of −1 (the charm sign agreeing with the quark charge sign).
As with other flavor-related quantum numbers, charm is preserved under strong and electromagnetic interaction, but not under weak interaction. For first-order weak reactions, it holds that | ΔC | = 1. The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... Electromagnetic interaction is a fundamental force of nature and is felt by charged leptons and quarks. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...
The number of generations of leptons with a light neutrino is strongly constrained by experiments at the LEP in CERN and by observations of the abundance of helium in the universe.
The additive quantumnumbers of antiquarks are equal in magnitude and opposite in sign to those of the quarks.
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.
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