muon

The negatively charged lepton that belongs to the second generation of elementary fermions and has a mass 207 times that of an electron and a mean lifetime of 2.2 × 10⁻⁶ second.

An unstable elementary particle in the lepton family, having similar properties to the electron but with a mass 209 times greater.

an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino