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

TL;DR

This study searches for neutrino-induced neutral current $$ radiative decay in MicroBooNE data, constraining anomalous rates and testing the hypothesis that MiniBooNE's low-energy excess is due to single-photon events, with significant improvements over previous limits.

Contribution

It provides the first constraints on NC $$ radiative decay in MicroBooNE and tests the single-photon hypothesis for MiniBooNE's excess, improving existing limits by over 50-fold.

Findings

Bound on anomalous NC $$ radiative decay rate less than 2.3 times the nominal prediction.

Disfavors the hypothesis that MiniBooNE excess is due to single-photon events, with data consistent with the nominal rate.

Significantly improves the limit on single-photon production in NC interactions in the sub-GeV neutrino energy range.

Abstract

We report results from a search for neutrino-induced neutral current (NC) resonant $\Delta$(1232) baryon production followed by $\Delta$ radiative decay, with a $\langle0.8\rangle$~GeV neutrino beam. Data corresponding to MicroBooNE's first three years of operations (6.80$\times$10$^{20}$ protons on target) are used to select single-photon events with one or zero protons and without charged leptons in the final state ($1\gamma1p$ and $1\gamma0p$, respectively). The background is constrained via an in-situ high-purity measurement of NC $\pi^0$ events, made possible via dedicated $2\gamma1p$ and $2\gamma0p$ selections. A total of 16 and 153 events are observed for the $1\gamma1p$ and $1\gamma0p$ selections, respectively, compared to a constrained background prediction of $20.5 \pm 3.65 \text{(sys.)} $ and $145.1 \pm 13.8 \text{(sys.)} $ events. The data lead to a bound on an anomalous enhancement of the normalization of NC $\Delta$ radiative decay of less than $2.3$ times the predicted nominal rate for this process at the 90% confidence level (CL). The measurement disfavors a candidate photon interpretation of the MiniBooNE low-energy excess as a factor of $3.18$ times the nominal NC $\Delta$ radiative decay rate at the 94.8% CL, 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