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 $|\Delta m^2|=(2.43\pm 0.13)\times {10}^{-3}{\mathrm{eV}}^2$ (68% C.L.) and mixing angle ${sin}^2(2\theta )>0.90$ (90% C.L.). 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.