Muon

A muon is an elementary charged lepton with the same electric charge as an electron and about 207 times its mass. It is unstable, decaying into an electron and two neutrinos.

Muon decay: The weak-interaction process in which a muon decays into an electron and two neutrinos. This is the muon’s characteristic fate and sets its finite lifetime.
Muon discovery: The identification of the particle now called the muon in cosmic-ray experiments in 1936. Its unexpected mass prompted the famous question of why nature needed a heavier electron-like particle.
Lepton: A family of elementary fermions that includes electrons, muons, taus, and neutrinos. The muon is the second charged member of the three-generation lepton family.
Muon tomography: An imaging technique that uses the scattering or absorption of naturally occurring cosmic-ray muons to map dense objects. Muons’ ability to penetrate thick material makes them useful for imaging structures inaccessible to ordinary scanning.
Pion: A meson made of a quark and an antiquark that commonly decays into a muon and a muon neutrino. Pion decay is a major source of muons in cosmic-ray showers and accelerator beams.
Muon lifetime: The mean time before an unstable muon decays: about 2.2 microseconds at rest. Its measured lifetime tests relativistic time dilation and weak-interaction theory.
Carl D. Anderson: An American physicist who discovered the positron and shared in the discovery of the muon. Anderson and Seth Neddermeyer reported the particle in cosmic-ray tracks.
Standard Model: The quantum field theory describing known elementary particles and three of the four fundamental interactions. It classifies the muon and predicts its interactions with other particles.
Muon spin spectroscopy: A materials research technique that implants spin-polarized muons and tracks their spin evolution. The muon’s spin acts as a sensitive probe of local magnetic fields in materials.
Proton: A composite, positively charged particle made of two up quarks and one down quark. Unlike the elementary muon, the proton is a quark composite and remains stable under ordinary conditions.

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