Double Chooz: Results and Perspectives

The Double Chooz experiment has been observing (nu) over bar (e) from two reactor cores at the Chooz nuclear power station in Ardennes, France, with a single 10.3 m(3) fiducial volume Gd-doped liquid scintillator detector at a flux-weighted average baseline of similar to 1050 m. This article reviews results achieved with a detector live time of 227.93 days and exposure of 33.71 GW-ton-years. A total of 8,249 candidate (nu) over bar (e) events have been observed, compared to an expected 8,937 events in the null-oscillation case: this deficit is interpreted as evidence for (nu) over bar (e) disappearance. A fit to the observed neutrino rate and spectral shape gives a best-fit value of sin(2) (2 theta(13)) = 0.109 +/- 0.030 (stat.) +/- 0.025 (syst.) at a mass-squared splitting of Delta m(31)(2) = 2.32 x 10(-3) eV(2). The null-oscillation hypothesis is excluded by the data at 99.8% CL (2.9 sigma). The Double Chooz Near Detector is under construction, and analysis efforts to measure neutrino directionality, test Lorentz violation, and measure backgrounds in situ are underway.