Measurement of Neutrino Oscillations with the MINOS Detectors in the NuMI Beam

This letter reports new results from the MINOS experiment based on a two-year exposure to muon neutrinos from the Fermilab NuMI beam. Our data are consistent with quantum mechanical oscillations of neutrino flavor with mass splitting $|\Delta m^2|=(2.43\pm 0.13)\times10^{-3}$ eV$^2$ (68% confidence level) and mixing angle $\sin^2(2\theta)>0.90$ (90% confidence level). Our data disfavor two alternative explanations for the disappearance of neutrinos in flight, namely neutrino decays into lighter particles and quantum decoherence of neutrinos, at the 3.7 and 5.7 standard deviation levels, respectively.