Definition of muon in US English:



  • An unstable subatomic particle of the same class as an electron (a lepton), but with a mass around 200 times greater. Muons make up much of the cosmic radiation reaching the earth's surface.

    • ‘The number of times that an antimuon emits a positron in the same direction as its polarization was found to be equal to the number of times that a muon emits an electron in the opposite direction.’
    • ‘The proton and the neutron are baryons; the electron, the muon, and the neutrino are leptons; whilst the pions are mesons.’
    • ‘Incidently, before the quark theory was invented to understand the properties of elementary particles the term ‘meson’ was also applies to muons - which are not made up of quarks but are fundamental point particles like the electron.’
    • ‘These objects also produce high-energy massive particles such as electrons, muons, protons and anti-protons.’
    • ‘Comsic rays are very high energy particles which strike the Earth's atmosphere and produce spectacular showers of billions of electrons, muons, and other particles.’


1950s: contraction of mu meson; the particle, however, is no longer regarded as a meson.