The mass of the Muon’s neutrino

Summary  We investigate the effects, on free muon production and decay, of a non-zero mass for the muon’s neutrino. The quantity most sensitive to the mass of the muon’s neutrino is the shape of the electron spectrum from isotropic Μ+-decay near the maximum electron energy. A probable upper limit of 5 electron masses is set on the neutrino’s mass using data on the maximum electron energy, but a more accurate evaluation is possible, with current experimental techniques, if data are obtained on the shape of the isotropic electron spectrum.