Sterile neutrino search at NEOS Experiment

TL;DR

The NEOS experiment searched for light sterile neutrinos using reactor antineutrino data, finding no evidence of oscillations and excluding certain parameter regions, while observing an excess around 5 MeV similar to other experiments.

Contribution

This study provides new constraints on sterile neutrino parameters by analyzing reactor antineutrino spectra with high precision and excluding specific oscillation hypotheses.

Findings

No evidence of active-sterile neutrino oscillations was found.

Excluded sterile neutrino mixing parameters with sin^2 2θ_14 below 0.1 for Δm^2_41 between 0.2 and 2.3 eV^2.

Observed an excess around 5 MeV in the antineutrino energy spectrum.

Abstract

An experiment to search for light sterile neutrinos was conducted at a reactor with a thermal power of 2.8 GW located at the Hanbit nuclear power complex. The search was done with a detector consisting of a ton of Gd-loaded liquid scintillator in a tendon gallery approximately 24 m from the reactor core. The measured antineutrino event rate is 1976 per day with a signal to background ratio of about 22. The shape of the antineutrino energy spectrum obtained from eight-month data-taking period is compared with a hypothesis of oscillations due to active-sterile antineutrino mixing. It is found to be consistent with no oscillation. An excess around 5 MeV prompt energy range is observed as seen in existing longer baseline experiments. The parameter space of $\sin^{2}2\theta_{14}$ down below 0.1 for $\Delta m^{2}_{41}$ ranging from 0.2 eV$^{2}$ to 2.3 eV$^{2}$ and the optimum point for the previously reported reactor antineutrino anomaly are excluded with a confidence level higher than 90%.