New results from the Double Chooz experiment

The Double Chooz experiment presents new results derived from data collected during 467.90 live days in a detector located 1050 m from two reactor cores at the Chooz Nuclear Power Plant. This improved θ 13 oscillation analysis relies on new techniques for reducing backgrounds and systematic uncertainties while increasing ν ‾ e signal efficiency. In a fit to the observed ν ‾ e rate and energy spectrum, the value of θ 13 is measured to be sin 2 ⁡ 2 θ 13 = 0.090 − 0.029 + 0.032 . A consistent and uniquely background-independent result, sin 2 ⁡ 2 θ 13 = 0.060 ± 0.039 , is obtained with a reactor rate modulation approach. While the precision of these results is still limited by reactor flux uncertainty, these analyses demonstrate powerful techniques which will reach their full potential when the second Double Chooz detector begins operation. In addition to the oscillation results, deviations from the reactor ν ‾ e prediction observed above a 4 MeV are reported.