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

TL;DR

The MiniBooNE Collaboration observes unexplained electronlike events in the reconstructed neutrino energy range from 200 to 475 MeV, and the shape of the excess in several kinematic variables is consistent with being due to either nu_{e} and nu[over ]_{e] charged-current scattering or nu_{mu} neutral- current scattering with a photon in the final state.

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 $ν_e$ and $\bar ν_e$ charged-current scattering or to $ν_μ$ 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.

Figures (5)

• Figure 1: The $E_\nu^{QE}$ distribution for data (points with statistical errors) and backgrounds (histogram with systematic errors).
• Figure 2: The event excess as a function of $E_\nu^{QE}$. Also shown are the expectations from the best oscillation fit and from neutrino oscillation parameters in the LSND allowed region lsnd. The error bars include both statistical and systematic errors.
• Figure 3: The event excess as a function of $E_{vis}$ for $E_\nu^{QE} > 200$ MeV. Also shown are the expectations from the best oscillation fit and from neutrino oscillation parameters in the LSND allowed region lsnd. The error bars include both statistical and systematic errors.
• Figure 4: The event excess as a function of $Q^2$ for $300 < E_\nu^{QE} < 475$ MeV. Also shown are the expected shapes from the NC $\pi^0$ and $\Delta \rightarrow N \gamma$ reactions, which are representative of photon events produced by NC scattering, and from CC $\nu_e C \rightarrow e^- X$ and $\bar{\nu}_e C \rightarrow e^+ X$ scattering. The error bars include both data statistical and shape-only systematic errors.
• Figure 5: The event excess as a function of $\cos (\theta)$ for $300 < E_\nu^{QE} < 475$ MeV. The legend is the same as Fig. \ref{['data_mc4']}.