Observation of electron-antineutrino disappearance at Daya Bay

TL;DR

The Daya Bay experiment observed a significant disappearance of electron antineutrinos over a baseline of about 1.6 km, providing precise measurement of the neutrino mixing angle θ13.

Contribution

This work provides the first high-significance measurement of θ13 using reactor antineutrinos with multiple detectors at different baselines.

Findings

Measured θ13 as 0.092 ± 0.017

Observed antineutrino deficit consistent with oscillations

Detected over 80,000 antineutrino events

Abstract

The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle $\theta_{13}$ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW$_{\rm th}$ reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GW_{\rm th}-day livetime exposure in 55 days, 10416 (80376) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is $R=0.940\pm 0.011({\rm stat}) \pm 0.004({\rm syst})$. A rate-only analysis finds $\sin^22\theta_{13}=0.092\pm 0.016({\rm stat})\pm0.005({\rm syst})$ in a three-neutrino framework.