Observation of a Significant Excess of Electron-Like Events in the MiniBooNE Short-Baseline Neutrino Experiment

<!--HTML--><p>The MiniBooNE experiment at Fermilab reports results from an analysis of electron neutrino (nue) appearance data from 1.3E21 protons on target (POT) in neutrino mode, an increase of approximately a factor of two over previously reported results (PRL110(2013)161801). A nue charged-current quasi-elastic&nbsp; (CCQE) event excess of 381.2 +/- 85.2 events (4.5sigma) is observed in the energy range 200 &lt; EnuQE &lt; 1250 MeV.</p> <p>Combining these data with the electron anti-neutrino (nuebar) appearance data from 1.1E21 POT in antineutrino mode, a total nue plus nuebar CCQE event excess of 460.5 +/- 95.8 events (4.8 sigma) is observed. If interpreted in a standard two-neutrino oscillation model (numu to nue), the best oscillation fit to the excess has a probability of 20.1% while the background-only fit has a chi2-probability of 5E-7 relative to the best fit. The MiniBooNE data are consistent in energy and magnitude with the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND). All of the major backgrounds are constrained by in-situ event measurements, so non-oscillation explanations would need to invoke new anomalous background processes. https://arxiv.org/abs/1805.12028</p>