Search forπ0→νμν¯μDecays in the LSND Detector

We observe a net beam excess of $8.7\ifmmode\pm\else\textpm\fi{}6.3(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\ifmmode\pm\else\textpm\fi{}2.4(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$ events, above 160 MeV, resulting from the charged-current reaction of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and/or ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ on C and H in the LSND detector. No beam-related muon background is expected in this energy regime. Within an analysis framework of ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$, we set a direct upper limit for this branching ratio of $\ensuremath{\Gamma}({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})/\ensuremath{\Gamma}({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\mathrm{a}\mathrm{l}\mathrm{l})l1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 90% confidence level.