First measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions using an accelerator neutrino beam

TL;DR

This paper presents the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current interactions using the Super-Kamiokande detector with an accelerator neutrino beam, providing new experimental data for neutrino interaction modeling.

Contribution

It introduces a novel measurement of neutron capture multiplicity in neutrino-oxygen interactions at T2K, utilizing neural networks for gamma-ray signal identification and comparing results with simulation predictions.

Findings

Measured mean neutron capture multiplicity: 1.37 ± 0.33 (stat.) ± 0.17-0.27 (syst.)

Observed discrepancy with simulation predictions within 2.3 sigma

Identified hadron-nucleus interaction modeling as a key source of systematic uncertainty

Abstract

We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasi-elastic-like event candidates were selected from T2K data corresponding to an exposure of $1.76\times10^{20}$ protons on target. The $\gamma$ ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be $1.37\pm0.33\text{ (stat.)}$$^{+0.17}_{-0.27}\text{ (syst.)}$, which is compatible within $2.3\,\sigma$ than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium.