bbbar
bbbar refers to a bound state of a bottom quark (b) and its antiquark (b̄). As a heavy quark–antiquark system, bb̄ is a central object in the study of quantum chromodynamics (QCD) in the nonrelativistic regime. The bottomonium family forms when the two heavy quarks remain bound as a color-singlet state, and it serves as a clean laboratory for testing QCD-inspired approaches such as potential models, lattice QCD, and nonrelativistic QCD (NRQCD).
The ground state of bottomonium is the Upsilon(1S), with a mass around 9.460 GeV. Excited states include
In high-energy collisions, bb̄ pairs are produced predominantly by gluon fusion and quark-antiquark annihilation. These pairs
Overall, bbbar systems, especially bottomonium, occupy a key place in hadron physics by bridging experimental measurements