Improved measurements of the neutrino mixing angle [theta] ^sub 13^ with the Double Chooz detector

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The Double Chooz experiment presents improved measurements of the neutrino mixing angle [theta] ^sub 13^ using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the ... signal has increased. The value of [theta] ^sub 13^ is measured to be sin^sup 2^2[theta] ^sub 13^=0.090^sub -0.029^^sup +0.032^ from a fit to the observed energy spectrum. Deviations from the reactor ... prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of [theta] ^sub 13^ is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the [theta] ^sub 13^ measurement despite the observed distortion. [Figure not available: see fulltext.]