Muon decay
= Muon decay
{title2=$\mu^-\to e^-\bar\nu_e\nu_\mu$}
A <weak charged current> decay described at energies much below the <W boson> mass by a <four-fermion interaction> with coefficient given by the <Fermi constant>. At leading order with negligible final-state masses, its width is $G_F^2m_\mu^5/(192\pi^3)$.