Inphysics,bottomness (symbolB′; using a prime as plainB is used already forbaryon number) orbeauty is aflavour quantum number reflecting the difference between the number ofbottom antiquarks (n
_b
) and the number ofbottom quarks (n
_b
) that are present in a particle:

${\displaystyle B^{\mathrm{\prime }}=-(n_b-n_{\overline{b}})}$

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 theelectric charge (symbolQ) of that quark (in this case, Q = −1⁄3).

As with other flavour-related quantum numbers, bottomness is preserved understrong andelectromagnetic interactions, but not underweak interactions. For first-order weak reactions, it holds that${\displaystyle \mathrm{\Delta }{B}^{\mathrm{\prime }}=\pm 1}$.

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].

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