M. Bishai

TL;DR: A measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrinos Experiment with nearly 4 million reactor ν[over ¯]_{e} inverse β decay candidates observed over 1958 days of data collection is reported.

Abstract: 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 νe’s. Comparison of the νe 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 νe disappearance. More than 2.5 million νe 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 νe 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 νe 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 2θ_(13)=0.0841±0.0027(stat)±0.0019(syst) and the effective neutrino mass-squared difference of |Δm^2_(ee)|=(2.50±0.06(stat)±0.06(syst))×10^(−3) eV^2. Analysis using the exact three-flavor probability found Δm^2_(32)=(2.45±0.06(stat)±0.06(syst))×10^(−3) eV^2 assuming the normal neutrino mass hierarchy and Δm^2_(32)=(−2.56±0.06(stat)±0.06(syst))×10^(−3) eV^2 for the inverted hierarchy.

TL;DR: Improvements in energy calibration limited variations between detectors to 0.2%.

TL;DR: In this article, a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment was reported.

TL;DR: While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ, indicating that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes.