bottomness

{{Short description|Term used in physics to refer to the number of bottom quarks}}

{{Flavour quantum numbers}}

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 (n_{{{SubatomicParticle|Bottom antiquark}}}) and the number of bottom quarks (n_{{{SubatomicParticle|Bottom quark}}}) that are present in a particle:

:$B^\backslash prime\; =\; -(n\_b\; -\; n\_\{\backslash bar\; b\})$

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 = −{{frac|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 $\backslash Delta\; B^\backslash prime\; =\; \backslash plusmn\; 1$.

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