Mesons

Mesons are hadronic subatomic particles composed of a quark and an antiquark bound by the strong interaction. They are color-neutral and, because they have integer spin, they are bosons. In the quark model, mesons arise as bound states of a quark and an antiquark with a variety of flavors and masses. Their properties are described by quantum numbers such as total angular momentum J, parity P, and (for neutral mesons) charge conjugation C. Light mesons can be arranged into SU(3) flavor nonets, including pions, kaons and the eta; heavier mesons contain charm or bottom quarks and form families such as D mesons and B mesons, as well as quarkonia like charmonium (c-cbar) and bottomonium (b-bbar). Light mesons are typically pseudoscalar (J^P = 0^−) or vector (J^P = 1^−), while heavier states span additional J^P values.

Mesons participate in the strong interaction as well as electromagnetic and weak interactions. They are typically unstable, decaying into lighter mesons, leptons, or photons. Production occurs in high-energy collisions and in the decay of heavier hadrons; light mesons also play a role in mediating the residual strong force between nucleons in phenomenological models (the pion exchange).

Experimentally, mesons are studied by detecting their production and their decay products. The meson spectrum and decay patterns provide tests of quantum chromodynamics, flavor physics and symmetry principles. Theoretical descriptions include potential models, lattice QCD and effective field theories.