Muon decay

Muon decay is the weak-interaction process in which a muon becomes an electron, an electron antineutrino, and a muon neutrino. It is a three-body decay with a continuous electron-energy spectrum.

Fermi's theory of beta decay: A low-energy theory describing weak decays through a pointlike interaction among four fermions. It models muon decay as a four-fermion interaction at energies far below the W boson mass.
Muon: A charged elementary lepton, about 207 times more massive than an electron, that decays through the weak interaction. Its mass permits decay into an electron while conserving energy and lepton number.
Enrico Fermi: An Italian physicist who formulated a theory of beta decay and made foundational contributions to nuclear and particle physics. His four-fermion theory also describes muon decay at low energies.
Muon g−2: Precision measurements of the muon's anomalous magnetic moment, the difference between its magnetic factor and the Dirac value. Experiments identify muon decays and infer the parent muon's spin from positron directions.
Beta decay: A weak nuclear process in which a neutron or proton changes type while emitting a beta particle and a neutrino or antineutrino. Both processes involve weak decay, but muon decay has no hadronic nucleus in its final state.
Charged-current interaction: A weak interaction mediated by a W boson that changes particle type and electric charge. A virtual W boson connects the muon to its neutrino and the electron to its antineutrino.
Electron neutrino: A neutral, nearly massless elementary particle that participates in weak interactions with electrons. Muon decay produces its antiparticle alongside the electron.
V–A theory: The description of weak interactions using vector-minus-axial-vector currents, developed in the 1950s and 1960s. Muon-decay spectra and polarization measurements helped establish the interaction's left-handed structure.
Muon lifetime experiment: An experiment that determines the muon mean lifetime by measuring the time distribution of decay electrons or positrons. The measured decay rate provides a precision determination of the Fermi constant.
Tau decay: The weak decay of a tau lepton into lighter leptons or hadrons and associated neutrinos. Like muon decay it is a charged-lepton decay, but the tau's greater mass permits many hadronic channels.

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