B–Bbar oscillation

B–Bbar oscillation refers to a phenomenon in particle physics involving B mesons, which are composite particles made up of a bottom quark (b) and either an up quark (u) or a down quark (d) (or their corresponding antiquarks). The term "Bbar" represents the antiparticle of the B meson, specifically consisting of a bottom antiquark and an up or down quark.