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Register a new userUpper limits for neutrino oscillations muon-antineutrino to electron-antineutrino from muon decay at rest
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The KARMEN experiment at the spallation neutron source ISIS used umub from mup--decay at rest in the search for neutrino oscillations umubnueb in the appearance mode, with p( ueb,e+)n as detection reaction of ueb. In total, 15 candidates fulfill all conditions for the ueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for umubnueb.
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A recently developed Standard-Model Extension (SME) formalism for neutrino oscillations that includes Lorentz and CPT violation is used to analyze the sidereal time variation of the neutrino event excess measured by the Liquid Scintillator Neutrino Detector (LSND) experiment. The LSND experiment, performed at Los Alamos National Laboratory, observed an excess, consistent with neutrino oscillations, of ${bar u}_e$ in a beam of ${bar u}_mu$. It is determined that the LSND oscillation signal is consistent with no sidereal variation. However, there are several combinations of SME coefficients that describe the LSND data; both with and without sidereal variations. The scale of Lorentz and CPT violation extracted from the LSND data is of order $10^{-19}$ GeV for the SME coefficients $a_L$ and $E times c_L$. This solution for Lorentz and CPT violating neutrino oscillations may be tested by other short baseline neutrino oscillation experiments, such as the MiniBooNE experiment.
Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the PMNS mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40{sigma} and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.
Data from the MINOS experiment has been used to search for mixing between muon neutrinos and muon antineutrinos using a time-independent Lorentz-violating formalism derived from the Standard-Model Extension (SME). MINOS is uniquely capable of searching for muon neutrino-antineutrino mixing given its long baseline and ability to distinguish between neutrinos and antineutrinos on an event-by-event basis. Neutrino and antineutrino interactions were observed in the MINOS Near and Far Detectors from an exposure of 10.56$times10^{20}$ protons-on-target from the NuMI neutrino-optimized beam. No evidence was found for such transitions and new, highly stringent limits were placed on the SME coefficients governing them. We place the first limits on the SME parameters $(c_{L})^{TT}_{mumu} $ and $(c_{L})^{TT}_{tautau}$ at $-8.4times10^{-23} < (c_{L})^{TT}_{mumu} < 8.0times10^{-23}$ and $-8.0times10^{-23} < (c_{L})^{TT}_{tautau} < 8.4times10^{-23}$, and the worlds best limits on the $tilde{g}^{ZT}_{muoverline{mu}}$ and $tilde{g}^{ZT}_{tauoverline{tau}}$ parameters at $|tilde{g}^{ZT}_{muoverline{mu}}| < 3.3times 10^{-23}$ and $|tilde{g}^{ZT}_{tauoverline{tau}}| < 3.3times 10^{-23}$, all limits quoted at $3sigma$.
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.
This letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for muon antineutrino production, accumulating an exposure of $1.71times 10^{20}$ protons on target. In the Far Detector, 97 charged current muon antineutrino events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at $6.3sigma$. The best fit to oscillation yields $Delta bar{m}^{2}=(3.36^{+0.46}_{-0.40}textrm{(stat.)}pm0.06textrm{(syst.)})times 10^{-3},eV^{2}$, $sin^{2}(2bar{theta})=0.86^{+0.11}_{-0.12}textrm{(stat.)}pm0.01textrm{(syst.)}$. The MINOS muon neutrino and muon antineutrino measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.
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