Improved measurements of the neutrino mixing angle $\theta_{13}$ with the Double Chooz detector

TL;DR

The Double Chooz experiment improved the measurement of the neutrino mixing angle θ13 by reducing backgrounds and systematics, achieving a more precise value from reactor neutrino data collected over 468 days.

Contribution

The paper introduces novel techniques for background reduction and systematic uncertainty mitigation, leading to an improved and more robust measurement of θ13.

Findings

Measured sin^2 2θ13 = 0.090^{+0.032}_{-0.029}

Observed deviations above 4 MeV prompt energy, with possible explanations

Consistent θ13 value obtained from rate and spectrum analyses

Abstract

The Double Chooz experiment presents improved measurements of the neutrino mixing angle $\theta_{13}$ 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 $\bar\nu_{e}$ signal has increased. The value of $\theta_{13}$ is measured to be $\sin^{2}2\theta_{13} = 0.090 ^{+0.032}_{-0.029}$ from a fit to the observed energy spectrum. Deviations from the reactor $\bar\nu_{e}$ prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of $\theta_{13}$ 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 $\theta_{13}$ measurement despite the observed distortion.