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Register a new userSearch for Sterile Neutrinos Mixing with Muon Neutrinos in MINOS
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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 $Delta m^{2}_{41} lesssim 1,mathrm{eV}^{2}$.
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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$^2$.
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.
We present limits on sterile neutrino mixing using 4,438 live-days of atmospheric neutrino data from the Super-Kamiokande experiment. We search for fast oscillations driven by an eV$^2$-scale mass splitting and for oscillations into sterile neutrinos instead of tau neutrinos at the atmospheric mass splitting. When performing both these searches we assume that the sterile mass splitting is large, allowing $sin^2(Delta m^2 L/4E)$ to be approximated as $0.5$, and we assume that there is no mixing between electron neutrinos and sterile neutrinos ($|U_{e4}|^2 = 0$). No evidence of sterile oscillations is seen and we limit $|U_{mu4}|^2$ to less than 0.041 and $|U_{tau4}|^2$ to less than 0.18 for $Delta m^2 > 0.8$ eV$^2$ at the 90% C.L. in a 3+1 framework. The approximations that can be made with atmospheric neutrinos allow these limits to be easily applied to 3+N models, and we provide our results in a generic format to allow comparisons with other sterile neutrino models.
Nuclear reactors are strong, pure and well localized sources of electron antineutrinos with energies in the few MeV range. Therefore they provide a suitable environment to study neutrino properties, in particular neutrino oscillation parameters. Recent predictions of the expected antineutrino flux at nuclear reactors are about 6% higher than the average rate measured in different experiments. This discrepancy, known as the reactor antineutrino anomaly, is significant at the 2.5{sigma} level. Several new experiments are searching for the origin of this observed neutrino deficit. One hypothesis to be tested is an oscillation to another neutrino state. In a three flavor model reactor neutrinos do not oscillate at baselines below 100 m. Hence, if such an oscillation is observed, it would imply the existence of at least one light sterile neutrino state not participating in weak interactions. Such a discovery would open the gate for new physics beyond the Standard Model.
The NESSiE Collaboration has been setup to undertake a conclusive experiment to clarify the {em muon--neutrino disappearance} measurements at short baselines in order to put severe constraints to models with more than the three--standard neutrinos. To this aim the current FNAL--Booster neutrino beam for a Short--Baseline experiment was carefully evaluated by considering the use of magnetic spectrometers at two sites, near and far ones. The detector locations were studied, together with the achievable performances of two OPERA--like spectrometers. The study was constrained by the availability of existing hardware and a time--schedule compatible with the undergoing project of multi--site Liquid--Argon detectors at FNAL. The settled physics case and the kind of proposed experiment on the Booster neutrino beam would definitively clarify the existing tension between the $ u_{mu}$ disappearance and the $ u_e$ appearance/disappearance at the eV mass scale. In the context of neutrino oscillations the measurement of $ u_{mu}$ disappearance is a robust and fast approach to either reject or discover new neutrino states at the eV mass scale. We discuss an experimental program able to extend by more than one order of magnitude (for neutrino disappearance) and by almost one order of magnitude (for antineutrino disappearance) the present range of sensitivity for the mixing angle between standard and sterile neutrinos. These extensions are larger than those achieved in any other proposal presented so far.
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