Direct experimental lower bound on the radiative lifetime of the muon neutrino

Abstract

A sensitive search for ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ decay into photons was performed in a high-intensity beam of neutrinos from ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\mu}}^{+}$ decay at rest. An upper limit of 68 possible $\ensuremath{\gamma}$-ray events was established, leading to a lower bound on the radiative lifetime of the muon (anti)neutrino of $\frac{\ensuremath{\tau}}{{m}_{{\ensuremath{\nu}}_{\ensuremath{\mu}}}}\ensuremath{\ge}15.4$ sec/eV (90% C.L.). This result represents more than a factor of 100 improvement over previous direct laboratory searches.