From HandWiki
Short description: Term used in physics to refer to the number of bottom quarks

In physics, bottomness (symbol B′; using a prime as plain B is used already for baryon number) or beauty is a flavour quantum number reflecting the difference between the number of bottom antiquarks (nb) and the number of bottom quarks (nb) that are present in a particle:

[math]\displaystyle{ B^\prime = -(n_b - n_{\bar b}) }[/math]

Bottom quarks have (by convention) a bottomness of −1 while bottom antiquarks have a bottomness of +1. The convention is that the flavour quantum number sign for the quark is the same as the sign of the electric charge (symbol Q) of that quark (in this case, Q = −​13).

As with other flavour-related quantum numbers, bottomness is preserved under strong and electromagnetic interactions, but not under weak interactions. For first-order weak reactions, it holds that [math]\displaystyle{ \Delta B^\prime = \plusmn 1 }[/math].

This term is rarely used. Most physicists simply refer to "the number of bottom quarks" and "the number of bottom antiquarks".


  • Anchordoqui, L.; Halzen, F. (2009). "Lessons in Particle Physics". arXiv:0906.1271 [physics.ed-ph].