Bottomness

In physics, bottomness (symbol B&prime;; 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 (nundefined) and the number of bottom quarks (nundefined) that are present in a particle:
 * $$ B^\prime = -(n_b - n_{\bar b})$$

Bottom quarks have (by convention) a bottomness of &minus;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 = &minus;$1/3$).

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 $$\Delta B^\prime = \plusmn 1$$.

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