Updated MiniBooNE neutrino oscillation results with increased data and new background studies

Abstract

The MiniBooNE experiment at Fermilab reports a total excess of $638.0\ifmmode\pm\else\textpm\fi{}52.1(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}122.2(\mathrm{syst}.)$ electronlike events from a data sample corresponding to $18.75\ifmmode\times\else\texttimes\fi{}{10}^{20}$ protons-on-target in neutrino mode, which is a 46% increase in the data sample with respect to previously published results and $11.27\ifmmode\times\else\texttimes\fi{}{10}^{20}$ protons-on-target in antineutrino mode. The overall significance of the excess, $4.8\ensuremath{\sigma}$, is limited by systematic uncertainties, assumed to be Gaussian, as the statistical significance of the excess is $12.2\ensuremath{\sigma}$. The additional statistics allow several studies to address questions on the source of the excess. First, we provide two-dimensional plots in visible energy and the cosine of the angle of the outgoing lepton, which can provide valuable input to models for the event excess. Second, we test whether the excess may arise from photons that enter the detector from external events or photons exiting the detector from ${\ensuremath{\pi}}^{0}$ decays in two model independent ways. Beam timing information shows that almost all of the excess is in time with neutrinos that interact in the detector. The radius distribution shows that the excess is distributed throughout the volume, while tighter cuts on the fiducial volume increase the significance of the excess. The data likelihood ratio disfavors models that explain the event excess due to entering or exiting photons.