Search for Muon-Neutrino to Electron-Neutrino Transitions in MINOS

This Letter reports on a search for ${\nu }_{\mu }\to {\nu }_e$ transitions by the MINOS experiment based on a $3.14\times {10}^{20}$ protons-on-target exposure in the Fermilab NuMI beam. We observe 35 events in the Far Detector with a background of $27\pm 5(\mathrm{stat})\pm 2(\mathrm{syst})$ events predicted by the measurements in the Near Detector. If interpreted in terms of ${\nu }_{\mu }\to {\nu }_e$ oscillations, this $1.5\sigma$ excess of events is consistent with ${sin}^2(2{\theta }_{13})$ comparable to the CHOOZ limit when $|\Delta m^2|=2.43\times {10}^{-3}{\mathrm{eV}}^2$ and ${sin}^2(2{\theta }_{23})=1.0$ are assumed.