# Search for neutral-current induced single photon production at the ND280 near detector in T2K

## TL;DR

This study searched for neutral-current induced single photon production at the T2K ND280 detector below 1 GeV, setting the first upper limit on the process in this energy range to inform neutrino oscillation experiments.

## Contribution

First search and upper limit setting for neutral-current single photon production below 1 GeV at T2K ND280 detector.

## Key findings

- No positive evidence found for the process.
- Set a model-dependent upper limit on the cross-section at 0.114×10⁻³⁸ cm² per nucleon.
- First limit established below 1 GeV for this process.

## Abstract

Neutrino neutral-current induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron-positron pairs, we achieved 95\% pure gamma ray sample from 5.738$\times 10^{20}$ protons-on-targets neutrino mode data. We do not find positive evidence of neutral current induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114$\times 10^{-38}$ cm$^2$ (90\% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of $\left<E_\nu\right>\sim 0.6$ GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.