Search for Sub-eV Sterile Neutrino at RENO

Abstract

We report a search result for a light sterile neutrino oscillation with roughly 2200 live days of data in the RENO experiment. The search is performed by electron antineutrino ($\overline{\hat{I}}{½}_e$) disappearance taking place between six 2.8 GW${}_{\text{th}}$ reactors and two identical detectors located at 294 m (near) and 1383 m (far) from the center of reactor array. A spectral comparison between near and far detectors can explore reactor $\overline{\hat{I}}{½}_e$ oscillations to a light sterile neutrino. An observed spectral difference is found to be consistent with that of the three-flavor oscillation model. This yields limits on ${\sin }^{2}2\hat{I}{¸}_{14}$ in the $10^{-4}\lesssim |\hat{I}”m_{41}^2|\lesssim 0.5$ eV${}^2$ region, free from reactor $\overline{\hat{I}}{½}_e$ flux and spectrum uncertainties. The RENO result provides the most stringent limits on sterile neutrino mixing at $|\hat{I}”m_{41}^2|\lesssim 0.002$ eV${}^2$ using the $\overline{\hat{I}}{½}_e$ disappearance channel.