The muon (; 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 , but with a much greater mass . It is classified as a lepton, together with the electron (mass ), the tau (mass ), and the three neutrinos (electron neutrino , muon neutrino and tau neutrino ). 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.