Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment
A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9 GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of ne's. Comparison of the ne rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ~1500 1950 m relative to detectors near the reactors ~350 600 m allowed a precise measurement of ne disappearance. More than 2.5 million ne inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011 July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012 July, 2015) The ne rate observed at the far detectors relative to the near detectors showed a significant deficit, R=0.949+ 0.002(stat) 0.002(syst) The energy dependence of ne disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three flavor oscillation probability yielded the flavor mixing angle sin^2 2th_(13)=0.0841+ 0.0027(stat) 0.0019(syst) and the effective neutrino mass squared difference of |Dm^2_(ee)(2.50+ 0.06(stat) 0.06(syst))x10^ 3) eV^2. Analysis using the exact three flavor probability found Dm^2_(32)(2.45+ 0.06(stat) 0.06(syst))x10^ 3) eV^2 assuming the normal neutrino mass hierarchy and Dm^2_(32) 2.56+ 0.06(stat) 0.06(syst))x10^ 3) eV^2 for the inverted hierarchy.