Muon

The muon (/ˈmjuːɒn/; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with electric charge of −1 e and a spin of ¹⁄₂, but with a much greater mass (7002105700000000000♠105.7 MeV/c²). It is classified as a lepton, together with the electron (mass 6999511000000000000♠0.511 MeV/c²), the tau (mass 7003177682000000000♠1776.82 MeV/c²), and the three neutrinos (electron neutrino ν
e, muon neutrino ν
μ and tau neutrino ν
τ). As is the case with other leptons, the muon is not believed to have any sub-structure—that is, it is not thought to be composed of any simpler particles.

The muon is an unstable subatomic particle with a mean lifetime of 6994220000000000000♠2.2 µs. Among all known unstable subatomic particles, only the neutron (lasting around 15 minutes) and some atomic nuclei have a longer decay lifetime; others decay significantly faster. The decay of the muon (as well as of the neutron, the longest-lived unstable baryon), is mediated by the weak interaction exclusively. Muon decay always produces at least three particles, which must include an electron of the same charge as the muon and two neutrinos of different types.