In Physics, Bottomness (also formerly called Beauty) quantum number is the number of bottom anti-quarks (
) minus the number of bottom quarks (b) that are present in a particle:
Bottom quarks have a bottomness of −1 and bottom anti-quarks of +1, so the bottomness sign agrees with its charge ( - 1 / 3 for b).
As with other flavor-related quantum numbers, bottomness is preserved under strong and electromagnetic interaction, but not under weak interaction. For firt-order weak reactions, it holds that 
.
See also