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	Flavour in particle physics v • d • e
	Flavour quantum numbers: Baryon number: B; Lepton number: L; Strangeness: S; Charmness: C; Bottomness: B′; Topness: T; Isospin: I or I3; Weak isospin: T or T3; Electric charge: Q; Combinations: Hypercharge: Y Y = (B + S + C + B′ + T); Y = 2 (Q − I3); ; Weak hypercharge: YW YW = 2 (Q − T3); X + 2YW = 5 (B − L); ; Flavour mixing CKM matrix; PMNS matrix; Flavour complementarity;

In physics, bottomness (symbol B′) also formerly 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".

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