This paper reports measurements of atmospheric neutrino and antineutrino interactions in the MINOS Far Detector, based on 2553 live-days (37.9 kton-years) of data. A total of 2072 candidate events are observed. These are separated into 905 contained-vertex muons and 466 neutrino-induced rock-muons, both produced by charged-current $\nu_{ \mu}$ and $\bar{ \nu}_{ \mu}$ interactions, and 701 contained-vertex showers, composed mainly of charged-current $\nu_{ e}$ and $\bar{ \nu}_{ e}$ interactions and neutral-current interactions. The curvature of muon tracks in the magnetic field of the MINOS Far Detector is used to select separate samples of $\nu_{ \mu}$ and $\bar{ \nu}_{ \mu}$ events. The observed ratio of $\bar{ \nu}_{ \mu}$ to $\nu_{ \mu}$ events is compared with the Monte Carlo simulation, giving a double ratio of $R^{ data}_{ \bar{ \nu}/\nu}/R^{ MC}_{ \bar{ \nu}/\nu} = 1.03 \pm 0.08 (stat.) \pm 0.08 (syst.)$. The $\nu_{ \mu}$ and $\bar{ \nu}_{ \mu}$ data are separated into bins of $L/E$ resolution, based on the reconstructed energy and direction of each event, and a maximum likelihood fit to the observed $L/E$ distributions is used to determine the atmospheric neutrino oscillation parameters. This fit returns 90% confidence limits of $|\Delta m^{ 2}| = (1.9 \pm 0.4) \times 10^{ -3} eV^{ 2}$ and $sin^{ 2} 2\theta > 0.86$. The fit is extended to incorporate separate $\nu_{ \mu}$ and $\bar{ \nu}_{ \mu}$ oscillation parameters, returning 90% confidence limits of $|\Delta m^{ 2}|-|\Delta \bar{ m}^{ 2}| = 0.6^{ +2.4}_{ -0.8} \times 10^{ -3} eV^{ 2}$ on the difference between the squared-mass splittings for neutrinos and antineutrinos.
Categories: hep-ex