Bottomness

Term used in physics to refer to the number of bottom quarks
Flavour in
particle physics
Flavour quantum numbers
  • Isospin: I or I3
  • Charm: C
  • Strangeness: S
  • Topness: T
  • Bottomness: B′
Related quantum numbers
  • Baryon number: B
  • Lepton number: L
  • Weak isospin: T or T3
  • Electric charge: Q
  • X-charge: X
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
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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
b
) and the number of bottom quarks (n
b
) that are present in a particle:

B ′ = − ( n b − n b ¯ ) {\displaystyle 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 Δ B ′ = ± 1 {\displaystyle \Delta B^{\prime }=\pm 1} .

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

References

  • Anchordoqui, L.; Halzen, F. (2009). "Lessons in Particle Physics". arXiv:0906.1271 [physics.ed-ph].


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