New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay

Abstract

We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×105 GWth-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six 241Am-13C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin2 2θ13 and |∆m2 ee| were halved as a result of these improvements.Analysisoftherelativeantineutrinoratesandenergyspectrabetweendetectorsgave sin2 2θ13 = 0.084±0.005and |∆m2 ee| = (2.42±0.11)×10−3 eV2 in the three-neutrino framework.