Search for Heavy Neutrinos in $K^{+}\to {\mu }^{+}{\nu }_{\mu }$ Decays

Abstract

The NA62 experiment recorded a large sample of $K^{+}\to {\mu }^{+}{\nu }_{\mu }$ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range $2\times 10^{-6}$ to $10^{-5}$ have been set on the squared mixing matrix element $|U_{\mu 4}{|}^2$ between muon and heavy neutrino states, for heavy neutrino masses in the range 300-375 MeV/$c^2$. The result extends the range of masses for which upper limits have been set on the value of $|U_{\mu 4}{|}^2$ in previous production search experiments.

12 pages, 8 figures. Published in Physics Letters B