Observation of Reactor Electron Antineutrino Disappearance in the RENO Experiment

TL;DR

The RENO experiment observed a significant deficit in reactor electron antineutrinos, confirming neutrino oscillations and measuring the mixing angle θ13 with high precision.

Contribution

This paper reports the first observation of reactor electron antineutrino disappearance at RENO, providing a precise measurement of θ13 using two detectors at different distances.

Findings

Observed a 8% deficit in antineutrino flux at the far detector.

Measured sin^2 2θ13 = 0.113 ± 0.013 (stat.) ± 0.019 (syst.).

Achieved a 4.9 sigma significance for neutrino oscillation evidence.

Abstract

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.