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Register a new userSearch for sterile neutrinos in MINOS and MINOS+ using a two-detector fit
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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$^2$.
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We report results of a search for oscillations involving a light sterile neutrino over distances of 1.04 and $735,mathrm{km}$ in a $ u_{mu}$-dominated beam with a peak energy of $3,mathrm{GeV}$. The data, from an exposure of $10.56times 10^{20},textrm{protons on target}$, are analyzed using a phenomenological model with one sterile neutrino. We constrain the mixing parameters $theta_{24}$ and $Delta m^{2}_{41}$ and set limits on parameters of the four-dimensional Pontecorvo-Maki-Nakagawa-Sakata matrix, $|U_{mu 4}|^{2}$ and $|U_{tau 4}|^{2}$, under the assumption that mixing between $ u_{e}$ and $ u_{s}$ is negligible ($|U_{e4}|^{2}=0$). No evidence for $ u_{mu} to u_{s}$ transitions is found and we set a world-leading limit on $theta_{24}$ for values of $Delta m^{2}_{41} lesssim 1,mathrm{eV}^{2}$.
The MINOS/MINOS+ experiment has recently reported stringent limits on $ u_mu$ disappearance that appear to rule out the 3+1 sterile neutrino model. However, in this paper we wish to point out problems associated with the MINOS/MINOS+ analysis. In particular, we find that MINOS/MINOS+ has either underestimated their systematic errors and/or has obtained evidence for physics beyond the 3-neutrino paradigm. Either case would invalidate the limits on $ u_mu$ disappearance.
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.
We searched for a sidereal modulation in the MINOS far detector neutrino rate. Such a signal would be a consequence of Lorentz and CPT violation as described by the Standard-Model Extension framework. It also would be the first detection of a perturbative effect to conventional neutrino mass oscillations. We found no evidence for this sidereal signature and the upper limits placed on the magnitudes of the Lorentz and CPT violating coefficients describing the theory are an improvement by factors of $20-510$ over the current best limits found using the MINOS near detector.
The MINOS experiment ran from 2003 until 2012 and collected a data sample including 10.71x10^20 protons-on-target (POT) of beam neutrinos, 3.36x10^20 POT of beam antineutrinos and an atmospheric neutrino exposure of 37.88 kt-yrs. The final measurement of the atmospheric neutrino oscillation parameters, dm^2_32 and theta_23, came from a full three flavour oscillation analysis of the combined CC nu_mu and CC anti-nu_mu beam and atmospheric samples and the CC nu_e and CC anti-nu_e appearance samples. This analysis yielded the most precise measurement of the atmospheric mass splitting dm^2_32 performed to date. The results are |dm^2_32|=[2.28 - 2.46]x10^-3 eV^2 (68%) and sin^{2}theta_23=0.35-0.65$ (90%) in the normal hierarchy, and |dm^2_32|=[2.32 - 2.53]x10^-3 eV^2 (68%) and sin^{2}theta_23=0.34-0.67 (90%) in the inverted hierarchy. The successor to MINOS in the NOvA era at FNAL, MINOS+, is now collecting data mostly in the 3-10 GeV region, and an analysis of nu_mu disappearance using the first 2.99x10^20 POT of data produced results very consistent with those from MINOS. Future data will further test the standard neutrino oscillation paradigm and allow for improved searches for exotic phenomena including sterile neutrinos, large extra dimensions and non-standard interactions.
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