Search for an anomalous excess of charged-current quasi-elastic $\hat{I}{½}_e$ interactions with the MicroBooNE experiment using Deep-Learning-based reconstruction

Abstract

We present a measurement of the $\hat{I}{½}_e$-interaction rate in the MicroBooNE detector that addresses the observed MiniBooNE anomalous low-energy excess (LEE). The approach taken isolates neutrino interactions consistent with the kinematics of charged-current quasi-elastic (CCQE) events. The topology of such signal events has a final state with 1 electron, 1 proton, and 0 mesons ($1e1p$). Multiple novel techniques are employed to identify a $1e1p$ final state, including particle identification that use two methods of deep-learning-based image identification, and event isolation using a boosted decision-tree ensemble trained to recognize two-body scattering kinematics. This analysis selects 25 $\hat{I}{½}_e$-candidate events in the reconstructed neutrino energy range of 200--1200\,MeV, while $29.0\pm 1.9_{\text{(sys)}}\pm 5.4_{\text{(stat)}}$ are predicted when using $\hat{I}{½}_{\hat{I}}¼$ CCQE interactions as a constraint. We use a simplified model to translate the MiniBooNE LEE observation into a prediction for a $\hat{I}{½}_e$ signal in MicroBooNE. A $\hat{I}”\ddot{I}{‡}^2$ test statistic, based on the combined Neyman--Pearson $\ddot{I}{‡}^2$ formalism, is used to define frequentist confidence intervals for the LEE signal strength. Using this technique, in the case of no LEE signal, we expect this analysis to exclude a normalization factor of 0.75 (0.98) times the median MiniBooNE LEE signal strength at 90\% ($2\ddot{I}ƒ$) confidence level, while the MicroBooNE data yield an exclusion of 0.25 (0.38) times the median MiniBooNE LEE signal strength at 90\% ($2\ddot{I}ƒ$) confidence