An elementary particle having the same charge and spin as an electron, but a mass 207 times greater. It is a lepton which decays into electrons and neutrinos with a half-life of two microseconds. Muons are present in cosmic-ray showers which are detected on Earth. Muons are produced by the decay of pions. Muons were once known as mu-mesons, but they are not mesons.
Subjects: Astronomy and Astrophysics.