Unexplained Excess of Electron-Like Events From a 1-GeV Neutrino Beam

TL;DR

The MiniBooNE experiment reports an unexplained excess of electron-like events at 200-475 MeV in a neutrino beam, suggesting potential new physics or unaccounted backgrounds, with no excess observed at higher energies.

Contribution

This paper presents the first observation of a significant excess of electron-like events in MiniBooNE at low energies, highlighting a possible anomaly in neutrino interactions.

Findings

544 electron-like events observed vs. 415 expected

Excess of 128.8 events with statistical significance

No excess observed at higher energies (475-1250 MeV)

Abstract

The MiniBooNE Collaboration observes unexplained electron-like events in the reconstructed neutrino energy range from 200 to 475 MeV. With $6.46 \times 10^{20}$ protons on target, 544 electron-like events are observed in this energy range, compared to an expectation of $415.2 \pm 43.4$ events, corresponding to an excess of $128.8 \pm 20.4 \pm 38.3$ events. The shape of the excess in several kinematic variables is consistent with being due to either $\nu_e$ and $\bar \nu_e$ charged-current scattering or to $\nu_\mu$ neutral-current scattering with a photon in the final state. No significant excess of events is observed in the reconstructed neutrino energy range from 475 to 1250 MeV, where 408 events are observed compared to an expectation of $385.9 \pm 35.7$ events.