Bottomness

In physics, bottomness (symbol B′) also called beauty, is a flavour quantum number reflecting the difference between the number of bottom antiquarks (n_b) and the number of bottom quarks (n_b) that are present in a particle:

$B^\prime = -(n_b - n_{\bar b})$

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 = −​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".