This letter reports on a search for $\nu_\mu \to \nu_e$ transitions by the MINOS experiment based on a \unit[$3.14\times10^{ 20}$]{ protons-on-target} exposure in the Fermilab NuMI beam. We observe 35 events in the Far Detector with a background of $27\pm 5 { \rm (stat.)} \pm 2 { \rm (syst.)$ 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 $|\delmsq{ }|$=\unit[2.43$\times 10^{ -3}$] { ${ \rm eV^{ 2}}$} and \sinsq{ 23}=1.0 are assumed.
Categories: hep-ex