Heng, Y (reprint author), Inst High Energy Phys, Beijing 100049, Peoples R China.
The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle theta(13) with a significance of 7.7 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected by six 20-ton target-mass detectors of identical design, deployed in two near and one far underground experimental halls. With a 116.8 kton-GWth-day live-time exposure in 139 days, 28,909 and 205,308 electron-antineutrino candidates were detected at the far hall and near halls respectively. The ratio of the observed to expected number of antineutrinos at the far hall is R = 0.944 +/- 0.007(stat) +/- 0.003(syst). A rate-only analysis finds sin(2)2 theta(13) = 0.089 +/- 0.010(stat) +/- 0.005(syst) in a three-neutrino framework. The experiments will continue for several years and a more precise neutrino mixing angle theta(13) will be given in the future.