Sterile neutrino search at NEOS Experiment

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 ${\sin }^{2}2\hat{I}{¸}_{14}$ down below 0.1 for $\hat{I}”m_{41}^2$ 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%.

6 pages, 4 figures. 1 supplemental material (Fig. S1). Version published in Physical Review Letters