Charm is the number of charm quarks (c) minus the number of charm anti-quarks () that are present in a particle:

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 firt-order weak reactions, it holds that | ΔC | = 1.

See also

• Isospin
• Strangeness
• Bottomness
• Topness
• Hypercharge