Measurements of Atmospheric Neutrinos and Antineutrinos in the MINOS Far Detector

Abstract

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 νμ and ν̅μ interactions, and 701 contained-vertex showers, composed mainly of charged-current νe and ν̅e 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 νμ and ν̅μ events. The observed ratio of ν̅μ to νμ events is compared with the Monte Carlo (MC) simulation, giving a double ratio of Rdataν̅/ν/RMCν̅/ν=1.03±0.08(stat)±0.08(syst). The νμ and ν̅μ 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 |Δm2|=(1.9±0.4)×10−3 eV2 and sin22θ>0.86. The fit is extended to incorporate separate νμ and ν̅μ oscillation parameters, returning 90% confidence limits of |Δm2|−|Δm̅2|=0.6+2.4−0.8×10−3 eV2 on the difference between the squared-mass splittings for neutrinos and antineutrinos.