MicroBooNE's First Search for the MiniBooNE Anomalous Excess Under a Photon-Like Hypothesis with High-Sensitivity Search for Neutrino-Induced Neutral Current Delta Production and Radiative Decay

Abstract

MicroBooNE is a liquid argon time projection chamber that collected neutrino data at Fermilab's Booster Neutrino Beam from 2015 to 2020. One of its primary goals is to investigate the “Low Energy Excess” of neutrino events observed by the MiniBooNE experiment, for which candidate photon-like interpretations include an underestimation of neutrino neutral current (NC) resonant Δ production with subsequent radiative decay or another anomalous source of single photon production in neutrino interactions. In particular, NC Δ radiative decay is poorly constrained background process to electron neutrino measurements and could be a sizable contribution to the “Low Energy Excess.” This thesis will present the analysis developed to search for NC Δ → N events in MicroBooNE, consisting of a boosted decision tree based event selection with an NC neutral pion background constraint, using data from the first three years of operations corresponding to 6.9 × 10²⁰ POT