Text: Muon The muon is a lepton which decays to form an electron or positron. The fact that the above decay is a three-particle decay is an example of the conservation of lepton number; there must be one electron neutrino and one muon neutrino or antineutrino in the decay. The lifetime of the muon is 2.20 microseconds. The muon is produced in the upper atmosphere by the decay of pions produced by cosmic rays: Measuring the flux of muons of cosmic ray origin at different heights above the earth is an important time dilation experiment in relativity. Muons make up more than half of the cosmic radiation at sea level, the remainder being mostly electrons, positrons and photons from cascade events.(Richtmyer) The average sea level muon flux is about 1 muon per square centimeter per second.

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