Muon
The
muon (/ˈmjuːɒn/; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with unitary negative electric charge of −1 and a spin of 1⁄2, but with a much greater mass (105.7 MeV/
c2). It is classified as a lepton, together with the electron (mass 0.511 MeV/
c2), the tau (mass 1777.8 MeV/
c2), and the three neutrinos. As is the case with other leptons, the muon is not believed to have any sub-structure; namely, it is not thought to be composed of any simpler particles. The muon is an unstable subatomic particle with a mean lifetime of 2.2 µs. Among all known subatomic particles, only the neutron 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.