Observation of Electron-Antineutrino Disappearance at Daya Bay

TLDR

The Daya Bay experiment detected electron‑antineutrinos from six 2.9 GWth reactors using six detectors in two near halls (470 m and 576 m) and one far hall (1648 m), accumulating 43 000 ton‑GWth‑day of exposure over 55 days and observing 10 416 far‑hall and 80 376 near‑hall candidates. The experiment observed a 5.2‑σ nonzero value of sin²2θ₁₃ = 0.092 ± 0.016(stat) ± 0.005(syst), with the far‑hall antineutrino rate ratio R = 0.940 ± 0.011(stat) ± 0.004(syst).

Abstract

The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle ${\ensuremath{\theta}}_{13}$ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 $\mathrm{G}{\mathrm{W}}_{\mathrm{th}}$ 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 $43\text{ }000\text{ }\text{ }\mathrm{ton}--\mathrm{G}{\mathrm{W}}_{\mathrm{th}}--\mathrm{day}$ live-time exposure in 55 days, 10 416 (80 376) 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 $R=0.940\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0ex}{0ex}}0.011(\mathrm{stat}.) \ifmmode\pm\else\textpm\fi{}0.004(\mathrm{syst}.)$. A rate-only analysis finds ${sin}^{2}2{\ensuremath{\theta}}_{13}=0.092\ifmmode\pm\else\textpm\fi{}0.016(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.005(\mathrm{syst}.)$ in a three-neutrino framework.