"A heavy counterpart to the electron, a lepton with a mass 206.7683 times that of the electron, but otherwise identical to an electron. The muon is unstable, with a half life of 2.19709 microseconds, and decays into an electron, a muon neutrino and an electron antineutrino." - p. 245 of John Gribbins Enclyclopedia of Particle Physics, Q is for Quantum