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Register a new userUpdated Search for Electron Antineutrino Appearance at MiniBooNE
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Authors
E. D. Zimmerman
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The MiniBooNE experiment at Fermilab has updated its search for u_mu-bar -> u_e-bar oscillations with data collected through May 2011. This represents a statistics increase of 52% over the result published in 2010. The data favor LSND-like oscillations over a background-only hypothesis at the 91.1% confidence level. While the new result remains equally consistent with LSND, the compatibility with the background-only hypothesis is improved. An excess of 38.6 +- 18.5 u_e-like events below 475 MeV is observed, consistent with the observation of such an excess in neutrino mode.
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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.
The MiniBooNE experiment has reported a number of high statistics neutrino and anti-neutrino cross sections-among which are the charged current quasi-elastic (CCQE) and neutral current elastic (NCE) neutrino scattering on mineral oil. Recently a study of the neutrino contamination of the anti-neutrino beam has concluded and the analysis of the anti-neutrino CCQE and NCE scattering is ongoing.
A search for a time-varying $bar{ u}_{e}$ signal was performed with 621 days of data acquired by the Daya Bay Reactor Neutrino Experiment over 704 calendar days. The time spectrum of the measured $overline{ u}_e$ flux normalized to its prediction was analyzed with a Lomb-Scargle periodogram, which yielded no significant signal for periods ranging from 2 hours to nearly 2 years. The normalized time spectrum was also fit for a sidereal modulation under the Standard Model extension (SME) framework to search for Lorentz and CPT violation (LV-CPTV). Limits were obtained for all six flavor pairs $bar{e}bar{mu}$, $bar{e}bar{tau}$, $bar{mu}bar{tau}$, $bar{e}bar{e},bar{mu}bar{mu}$ and $bar{tau}bar{tau}$ by fitting them one at a time, constituting the first experimental constraints on the latter three. Daya Bays high statistics and unique layout of multiple directions from three pairs of reactors to three experimental halls allowed the simultaneous constraint of individual SME LV-CPTV coefficients without assuming others contribute negligibly, a first for a neutrino experiment.
We report on $ u_e$ and $bar{ u}_e$ appearance in $ u_mu$ and $bar{ u}_mu$ beams using the full MINOS data sample. The comparison of these $ u_e$ and $bar{ u}_e$ appearance data at a 735 km baseline with $theta_{13}$ measurements by reactor experiments probes $delta$, the $theta_{23}$ octant degeneracy, and the mass hierarchy. This analysis is the first use of this technique and includes the first accelerator long-baseline search for $bar{ u}_murightarrowbar{ u}_e$. Our data disfavor 31% (5%) of the three-parameter space defined by $delta$, the octant of the $theta_{23}$, and the mass hierarchy at the 68% (90%) C.L. We measure a value of 2sin$^2(2theta_{13})$sin$^2(theta_{23})$ that is consistent with reactor experiments.
MiniBooNE (Mini Booster Neutrino Experiment) searches for the $ u_muto u_e$ oscillations with $Delta m^2 sim 1 eV^2/c^4$ indicated by the LSND experiment. The LSND evidence, when taken with the solar and atmospheric neutrino oscillations, suggests new physics beyond the Standard Model. However, this evidence has not been confirmed by other experiments. MiniBooNE has completed its first $ u_muto u_e$ oscillation search using a sample of $sim 1$ GeV neutrino events obtained with $5.58times 10^{20}$ protons delivered to the Booster Neutrino Beamline. The analysis finds no significant excess of $ u_e$ events in the analysis region of 475-3000 MeV.
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