First Measurement of \theta_13 from Delayed Neutron Capture on Hydrogen in the Double Chooz Experiment

TL;DR

The Double Chooz experiment measured the neutrino mixing parameter θ13 using neutron capture on hydrogen, expanding the fiducial volume and providing an independent analysis that confirms previous results within uncertainties.

Contribution

This is the first measurement of θ13 from neutron capture on hydrogen with a larger fiducial volume, offering an independent systematic check of previous Gd-based results.

Findings

Measured sin^2 2θ13 = 0.097 ± 0.034 (stat) ± 0.034 (syst)

Excluded no-oscillation hypothesis at 2.0 sigma

Results are consistent with previous θ13 measurements

Abstract

The Double Chooz experiment has determined the value of the neutrino oscillation parameter $\theta_{13}$ from an analysis of inverse beta decay interactions with neutron capture on hydrogen. This analysis uses a three times larger fiducial volume than the standard Double Chooz assessment, which is restricted to a region doped with gadolinium (Gd), yielding an exposure of 113.1 GW-ton-years. The data sample used in this analysis is distinct from that of the Gd analysis, and the systematic uncertainties are also largely independent, with some exceptions, such as the reactor neutrino flux prediction. A combined rate- and energy-dependent fit finds $\sin^2 2\theta_{13}=0.097\pm 0.034(stat.) \pm 0.034 (syst.)$, excluding the no-oscillation hypothesis at 2.0 \sigma. This result is consistent with previous measurements of $\sin^2 2\theta_{13}$.