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Register a new userProblems With the MINOS/MINOS+ Sterile Neutrino Muon-Neutrino Disappearance Result
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William C. Louis
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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.
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This letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rate and energy spectra of charged current muon neutrino interactions are compared in two detectors located along the beam axis at distances of 1 km and 735 km. With 1.27 x 10^{20} 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336 pm 14.4 events. The data are consistent with muon neutrino disappearance via oscillation with |Delta m^2_{23}| = 2.74^{+0.44}_{-0.26} x 10^{-3} eV^2/c^4 and sin^2(2theta_{23}) > 0.87 (at 60% C.L.).
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.
Searches for electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the $theta_{mu e}$ mixing angle are derived that constitute the most stringent limits to date over five orders of magnitude in the sterile mass-squared splitting $Delta m^2_{41}$, excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CL$_s$ for $Delta m^2_{41}<5,$eV$^2$.Furthermore, the LSND and MiniBooNE 99% C.L. allowed regions are excluded at 99% CL$_s$ for $Delta m^2_{41}$ $<$ 1.2 eV$^2$.
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 $Delta m^{2}_{41} lesssim 1,mathrm{eV}^{2}$.
We report the results of a search for $ u_{e}$ appearance in a $ u_{mu}$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2times10^{20}$ protons on the NuMI target at Fermilab, we find that $2sin^2(theta_{23})sin^2(2theta_{13})<0.12 (0.20)$ at 90% confidence level for $deltamathord{=}0$ and the normal (inverted) neutrino mass hierarchy, with a best fit of $2sin^2(theta_{23})sin^2(2theta_{13}),mathord{=},0.041^{+0.047}_{-0.031} (0.079^{+0.071}_{-0.053})$. The $theta_{13}mathord{=}0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.
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