Observation of Reactor Electron Antineutrino 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 GW$_{th}$ reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 m and 1383 m, respectively, from the reactor array center. In the 229 day 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 $0.920 \pm 0.009({\rm stat.}) \pm 0.014({\rm syst.})$. From this deficit, we determine $\sin^2 2 \theta_{13} = 0.113 \pm 0.013({\rm stat.}) \pm 0.019({\rm syst.})$ based on a rate-only analysis.