Observation of Reactor Electron Antineutrinos Disappearance in the RENO Experiment

The RENO experiment has observed the disappearance of reactor electron antineutrinos, consistent with neutrino oscillations, with a significance of 4.9 standard deviations. Antineutrinos from six $2.8{\mathrm{GW}}_{\mathrm{th}}$ reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 and 1383 m, respectively, from the reactor array center. In the 229 d data-taking period between 11 August 2011 and 26 March 2012, the far (near) detector observed 17102 (154088) electron antineutrino candidate events with a background fraction of 5.5% (2.7%). The ratio of observed to expected numbers of antineutrinos in the far detector is $0.920\pm 0.009(\mathrm{stat})\pm 0.014(\mathrm{syst})$. From this deficit, we determine ${sin}^{2}2{\theta }_{13}=0.113\pm 0.013(\mathrm{stat})\pm 0.019(\mathrm{syst})$ based on a rate-only analysis.