Search for Neutrino-Induced Neutral-Current Δ Radiative Decay in MicroBooNE and a First Test of the MiniBooNE Low Energy Excess under a Single-Photon Hypothesis

We report results from a search for neutrino-induced neutral current (NC) resonant Δ (1232 ) baryon production followed by Δ radiative decay, with a ⟨0.8 ⟩ GeV neutrino beam. Data corresponding to MicroBooNE's first three years of operations (6.80 ×10²⁰ protons on target) are used to select single-photon events with one or zero protons and without charged leptons in the final state (1 γ 1 p and 1 γ 0 p , respectively). The background is constrained via an in situ high-purity measurement of NC π⁰ events, made possible via dedicated 2 γ 1 p and 2 γ 0 p selections. A total of 16 and 153 events are observed for the 1 γ 1 p and 1 γ 0 p selections, respectively, compared to a constrained background prediction of 20.5 ±3.65 (syst ) and 145.1 ±13.8 (syst ) events. The data lead to a bound on an anomalous enhancement of the normalization of NC Δ radiative decay of less than 2.3 times the predicted nominal rate for this process at the 90% confidence level (C.L.). The measurement disfavors a candidate photon interpretation of the MiniBooNE low-energy excess as a factor of 3.18 times the nominal NC Δ radiative decay rate at the 94.8% C.L., in favor of the nominal prediction, and represents a greater than 50-fold improvement over the world's best limit on single-photon production in NC interactions in the sub-GeV neutrino energy range.