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Register a new userMeasurements of atmospheric neutrinos and antineutrinos in the MINOS Far Detector
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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 $ u_{mu}$ and $bar{ u}_{mu}$ interactions, and 701 contained-vertex showers, composed mainly of charged-current $ u_{e}$ and $bar{ u}_{e}$ 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 $ u_{mu}$ and $bar{ u}_{mu}$ events. The observed ratio of $bar{ u}_{mu}$ to $ u_{mu}$ events is compared with the Monte Carlo simulation, giving a double ratio of $R^{data}_{bar{ u}/ u}/R^{MC}_{bar{ u}/ u} = 1.03 pm 0.08 (stat.) pm 0.08 (syst.)$. The $ u_{mu}$ and $bar{ u}_{mu}$ 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 $sin^{2} 2theta > 0.86$. The fit is extended to incorporate separate $ u_{mu}$ and $bar{ u}_{mu}$ 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.
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A search for mixing between active neutrinos and light sterile neutrinos has been performed by looking for muon neutrino disappearance in two detectors at baselines of 1.04 km and 735 km, using a combined MINOS and MINOS+ exposure of $16.36times10^{20}$ protons-on-target. A simultaneous fit to the charged-current muon neutrino and neutral-current neutrino energy spectra in the two detectors yields no evidence for sterile neutrino mixing using a 3+1 model. The most stringent limit to date is set on the mixing parameter $sin^2theta_{24}$ for most values of the sterile neutrino mass-splitting $Delta m^2_{41} > 10^{-4}$ eV$^2$.
We have searched for sidereal variations in the rate of antineutrino interactions in the MINOS Near Detector. Using antineutrinos produced by the NuMI beam, we find no statistically significant sidereal modulation in the rate. When this result is placed in the context of the Standard Model Extension theory we are able to place upper limits on the coefficients defining the theory. These limits are used in combination with the results from an earlier analysis of MINOS neutrino data to further constrain the coefficients.
The charge ratio, $R_mu = N_{mu^+}/N_{mu^-}$, for cosmogenic multiple-muon events observed at an under- ground depth of 2070 mwe has been measured using the magnetized MINOS Far Detector. The multiple-muon events, recorded nearly continuously from August 2003 until April 2012, comprise two independent data sets imaged with opposite magnetic field polarities, the comparison of which allows the systematic uncertainties of the measurement to be minimized. The multiple-muon charge ratio is determined to be $R_mu = 1.104 pm 0.006 {rm ,(stat.)} ^{+0.009}_{-0.010} {rm ,(syst.)} $. This measurement complements previous determinations of single-muon and multiple-muon charge ratios at underground sites and serves to constrain models of cosmic ray interactions at TeV energies.
We report the first direct observation of muon antineutrinos in the MINOS Far Detector in the current muon-neutrino dominated beam. The magnetic field of the detector is utilized to separate muon neutrinos and antineutrinos event-by-event by identifying the charge sign of the muon created in charged-current interactions. We present preliminary results on the muon antineutrino oscillation parameters as well as limit on the fraction of neutrinos that disappear and reappear as antineutrinos. We also discuss the prospect of the measurement when the polarity of the magnetic focusing horns will be reversed to create a dedicated muon antineutrino beam.
We report the first observation of seasonal modulations in the rates of cosmic ray multiple-muon events at two underground sites, the MINOS Near Detector with an overburden of 225 mwe, and the MINOS Far Detector site at 2100 mwe. At the deeper site, multiple-muon events with muons separated by more than 8 m exhibit a seasonal rate that peaks during the summer, similar to that of single-muon events. In contrast and unexpectedly, the rate of multiple-muon events with muons separated by less than 5-8 m, and the rate of multiple-muon events in the smaller, shallower Near Detector, exhibit a seasonal rate modulation that peaks in the winter.
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