Meson

A type of hadron with whole-number units of spin. This family includes the pion, kaon, and eta. It is made up of a quark and its antimatter counterpart, bonded together. Mesons have a short mean life (less than 10^-8 second) because (in the case of pi-zero meson) the quark and antiquark can soon annihilate one another.

See also: Blackett, Patrick Maynard Stuart, Hadrons, Kaon, Pion.