Heavy-Neutrino Search UsingKμ2Decay

Abstract

The muon momentum spectrum in $K_{\mu 2}$ decay has been measured by using a high-resolution magnetic spectrograph to look for a discrete muon peak associated with heavy-neutrino emission. The spectrum revealed no distinct peak, and the upper bound of the mixing ratio between the muon neutrino and a massive neutrino has been determined to be ${10}^{-4\mathrm{}}$-${10}^{-6\mathrm{}}$ in the mass range of 70-300 MeV/${\mathit{c}}^2$.