Measurement of neutrino mixing angle theta(13) and mass difference Delta m(ee)(2) from reactor antineutrino disappearance in the RENO experiment

Abstract

RENO (Reactor Experiment for Neutrino Oscillation) made a definitive measurement of the smallest neutrino mixing angle theta(13) in 2012, based on the disappearance of reactor electron antineutrinos. The experiment has obtained a more precise value of the mixing angle and the first result on neutrino mass difference Delta m(ee)(2) from an energy and baseline dependent reactor neutrino disappearance using similar to 500 days of data. Based on the ratio of inverse-beta-decay (IBD) prompt spectra measured in two identical far and near detectors, we obtain sin(2)(2 theta(13)) = 0.082 +/- 0.009(stat.) +/- 0.006(syst.) and vertical bar Delta m(ee)(2)vertical bar = [2.62(-0.23+)(0.21)(stat.)(-0.13)(+0.12)(syst.)] x 10(-3) eV(2). An excess of reactor antineutrinos near 5 MeV is observed in the measured prompt spectrum with respect to the most commonly used models. The excess is found to be consistent with coming from reactors. A successful measurement of theta(13) is also made in an IBD event sample with a delayed signal of neutron capture on hydrogen. A precise value of theta(13) would provide important information on determination of the leptonic CP phase if combined with a result of an accelerator neutrino beam experiment. (C) 2016 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).