Indication of Reactor ν̅[subscript e] Disappearance in the Double Chooz Experiment

Abstract

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW[subscript th] reactors. The results were obtained from a single 10 m[superscript 3] fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin[superscript 2]2θ[subscript 13]. Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin[superscript 2]2θ[subscript 13]=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017<sin[superscript 2]2θ[subscript 13]<0.16.