Search

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 ($\overline{\nu}_e$) 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 $\overline{\nu}_e$ 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 $\sin^{2} 2\theta_{14}$ in the $10^{-4} \lesssim |\Delta m_{41}^2| \lesssim 0.5$ eV$^2$ region, free from reactor $\overline{\nu}_e$ flux and spectrum uncertainties. The RENO result provides the most stringent limits on sterile neutrino mixing at $|\Delta m^2_{41}| \lesssim 0.002$ eV$^2$ using the $\overline{\nu}_e$ disappearance channel.

We report a fuel-dependent reactor electron antineutrino ($\overline{\nu}_e$) yield using six 2.8 GW$_{\text{th}}$ reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses $850\,666$ $\overline{\nu}_e$ candidate events with a background fraction of 2.0 % acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel $^{235}$U dependent variation of measured IBD yields with a slope of $(1.51 \pm 0.23) \times 10^{-43} $cm$^2$/fission and measure a total average IBD yield of $(5.84 \pm 0.13) \times 10^{-43} $cm$^2$/fission. The hypothesis of no fuel-dependent IBD yield is ruled out at 6.6 $\sigma$. The observed IBD yield variation over $^{235}$U isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at 1.3 $\sigma$. The measured fuel-dependent variation determines IBD yields of $(6.15 \pm 0.19) \times 10^{-43} $cm$^2$/fission and $(4.18\pm 0.26) \times 10^{-43} $cm$^2$/fission for two dominant fuel isotopes $^{235}$U and $^{239}$Pu, respectively. The measured IBD yield per $^{235}$U fission shows the largest deficit relative to the HM prediction. Reevaluation of the $^{235}$U IBD yield per fission may mostly solve the Reactor Antineutrino Anomaly (RAA) while $^{239}$Pu is not completely ruled out as a possible contributor of the anomaly. We also report a 2.9 $\sigma$ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of $^{235}$U., Comment: 6 pages and 5 figures, v4 note: (1) data files for figure 1, figure 2, figure 5 are included for arXiv users (2) minor modifications in abstract and main text for clarification

The RENO experiment has analyzed about 500 live days of data to observe an energy dependent disappearance of reactor $\overline{\nu}_e$ by comparison of their prompt signal spectra measured in two identical near and far detectors. In the period between August 2011 and January 2013, the far (near) detector observed 31541 (290775) electron antineutrino candidate events with a background fraction of 4.9\% (2.8\%). The measured prompt spectra show an excess of reactor $\overline{\nu}_e$ around 5 MeV relative to the prediction from a most commonly used model. A clear energy and baseline dependent disappearance of reactor $\overline{\nu}_e$ is observed in the deficit of the observed number of $\overline{\nu}_e$. Based on the measured far-to-near ratio of prompt spectra, we obtain $\sin^2 2 \theta_{13} = 0.082 \pm 0.009({\rm stat.}) \pm 0.006({\rm syst.})$ and $|\Delta m_{ee}^2| =[2.62_{-0.23}^{+0.21}({\rm stat.}) _{-0.13}^{+0.12}({\rm syst.})]\times 10^{-3}$~eV$^2$., Comment: 6 pages, 5 figures, Accepted in PRL for publication

The RENO experiment is a short baseline neutrino experiment in Korea aiming to measure the neutrino mixing angle theta_13 or set limit to sin^2(2 theta_13) less than 0.02. This document describes physics goals, experimental site, detector design, scintillator, electronics, calibration, simulation, and physics reach., Comment: 126 pages, Technical Design Report