bottomantibottom

Bottomantibottom refers to the bound state formed by a bottom quark (b) and its antiquark (b̄), a system known in particle physics as bottomonium. The term emphasizes the quark–antiquark composition and is commonly represented in literature by the symbol bb̄.

The spectrum consists of vector states such as Upsilon(nS) with J^PC = 1^{--}, and P-wave states chi_bJ(nP) with J = 0, 1, 2. The masses lie in the bottomonium region of about 9.4–10.6 GeV, with ground state Upsilon(1S) at 9.46 GeV and excited states at higher masses. The states decay through strong, electromagnetic, and weak interactions, with most decaying into hadrons; electromagnetic decays to lepton pairs provide clean experimental signals.

Bottom–antibottom pairs are produced in high-energy processes, notably gluon fusion and heavy quark pair production in proton–proton or electron–positron collisions. Observables include production cross sections, branching fractions, and transition rates between bb̄ states via photon emission (e.g., Upsilon(3S) → γ Upsilon(1S)). Experiments at colliders study these systems to test quantum chromodynamics, potential models, and lattice QCD predictions.

This entry reflects the conventional usage of the bb̄ notation and does not imply any specific model beyond the standard quark model. The bottom–antibottom system serves as a benchmark for non-relativistic QCD and heavy-quark effective theories.