First results from the search for an excess of $\bar{\nu}_{e}$ events in JSNS$^2$

TL;DR

The JSNS$^2$ experiment conducted its first test to detect an excess of electron antineutrinos, finding results consistent with background expectations and setting the stage for future measurements to clarify the LSND anomaly.

Contribution

This paper presents the initial results of the JSNS$^2$ experiment testing for sterile neutrino signals, including the setup, data collection, and preliminary findings.

Findings

Observed 2 events, consistent with background of 2.3±0.4

Expected 1.1±0.5 events from LSND anomaly

Data collection ongoing with new detector for future runs

Abstract

The JSNS$^2$ (J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source) experiment at the Material and Life Science Facility (MLF) of J-PARC is designed to directly test an excess on $\bar{\nu}_{e}$ events which was indicated by LSND (Liquid Scintillator Neutrino Detector). The combination of a short-pulsed proton beam and a gadolinium-loaded liquid scintillator provides an excellent signal-to-noise ratio. In this article, we report the first results of a direct test based on data collected in 2022. After applying all event selection criteria, two events are observed, consistent with the expected background of 2.3$\pm$0.4 events. No excess of $\bar{\nu}_e$ events are seen in this report, however the expected number of events due to LSND anomaly is 1.1$\pm$0.5, thus this result is not yet conclusive. Data taking has been ongoing since 2021 and will continue in future runs. In addition, a new far detector has recently been constructed for the second phase experiment, JSNS$^2$-II, marking an important milestone toward forthcoming measurements.