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.

Figure 1

Energy spectra in the MINOS ND for two of the nine beam configurations before and after tuning the Monte Carlo simulation to the ND data. The data combine run I and run II. Both configurations are utilized in the oscillation analysis.

Figure 2

Comparison of the FD data (points, with statistical uncertainties) from the low- and high-energy configurations with the predictions for the ${\nu }_{\mu }$ energy spectra with and without the effect of oscillations. The estimated neutral-current (NC) background is indicated.

Figure 3

Ratio of the FD data and the expected spectrum in the absence of oscillations. Also shown are the best-fit curve to Eq. (1) and the best fit to alternative models of neutrino disappearance [10, 11]. For display purposes, the data have been rebinned and the estimated oscillated NC background is subtracted.

Figure 4

Contours for the oscillation fit to the data in Fig. 2, including systematic errors. Also shown are contours from previous experiments [1, 4] and our earlier result [8].