Any of a class of elementary particles that are a subclass of the hadrons. According to current quark theory mesons consist of quark–antiquark pairs. They exist with positive, negative, and zero charges, but when charged the charge has the same magnitude as that of the electron. They include the kaon, pion, and psi particles. Mesons are believed to participate in the forces that hold nucleons together in the nucleus, as described by quantum chromodynamics. The muon, originally called a mu-meson, was thought to be a meson but is now recognized as a lepton.
Subjects: Astronomy and Astrophysics — Physics.