In particle physics, mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of quark sub-particles, they have a physical size, with a diameter of roughly one fermi, which is about ?2?3 the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through mediating particles) to form electrons and neutrinos. Uncharged mesons may decay to photons. Both of these decays imply that color is no longer a property of the byproducts.
Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter, between particles made of quarks, such as the collision of cosmic rays made of nuclei (ordinary protons and neutrons). Mesons are also frequently produced artificially in high-energy particle accelerators in the collisions of protons, anti-protons, or other particles. Wikipedia, Meson
See Also
D-Meson
Chapter 6 - The True Nature of Electricity and Gravitation - I, page 129