An Etymological Dictionary of Astronomy and Astrophysics
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A → subatomic particle produced when → primary cosmic rays, impinge on the Earth's atmosphere producing a particle cascade, in which secondary particles decay into → muons. In the energy range up to 100 → GeV atmospheric muons come mostly from the decay of secondary → pions: π^±→ μ^± + anti-ν_μ. At higher energies, the → kaon contribution to the muon flux become significant, reaching the asymptotic value of 27% at about 10 TeV: K^±→ μ^± + anti-ν_μ.

→ atmospheric; → muon.

A short-lived → elementary particle with negative → electric charge, represented by the symbol μ^-. The muon was discovered in 1936 by Carl Anderson (1905-1991) in → cosmic rays. It shares several properties with the electron: it is a → lepton with the same charge and → spin as the electron. But it is heavier than the electron (105 MeV/c²), about 200 times more massive. The muon is instable and decays after 2.197 × 10^-6 s into → electron, → neutrino, and → antineutrino (μ^-→ e^- + ν_μ + anti ν_e) .

A shortening of mu meson, from mu the 12th letter of the Gk. alphabet, + → meson.

An → instrument used in → geophysics to determine the average → density of geological bodies by measuring the → attenuation produced by → rocks on the flux of → atmospheric muons. This density muon → radiography is or example used to study the physical conditions inside → volcanoes.

→ muon; → telescope.