The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle ${\theta }_{13}$ 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 $43000\mathrm{ton}–\mathrm{G}{\mathrm{W}}_{\mathrm{th}}–\mathrm{day}$ 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 $R=0.940\pm 0.011(\mathrm{stat}.)\pm 0.004(\mathrm{syst}.)$. A rate-only analysis finds ${sin}^{2}2{\theta }_{13}=0.092\pm 0.016(\mathrm{stat}.)\pm 0.005(\mathrm{syst}.)$ in a three-neutrino framework.

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor ${\overline{\nu }}_e$ inverse $\beta$ decay candidates observed over 1958 days of data collection. The installation of a flash analog-to-digital converter readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic ${}^9\mathrm{Li}$ and ${}^8\mathrm{He}$ background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative ${\overline{\nu }}_e$ rates and energy spectra among detectors yields ${\sin }^{2}2{\theta }_{13}=0.0856\pm 0.0029$ and $\mathrm{\Delta }{m}_{32}^2=({2.471}_{-0.070}^{+0.068})\times {10}^{-3}{\mathrm{eV}}^2$ assuming the normal hierarchy, and $\mathrm{\Delta }{m}_{32}^2=-({2.575}_{-0.070}^{+0.068})\times {10}^{-3}{\mathrm{eV}}^2$ assuming the inverted hierarchy.

We report an improved measurement of the neutrino mixing angle theta(13) from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for sin(2)2 theta(13) with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GW(th) were detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is 0.944 +/- 0.007(stat.)+/- 0.003(syst.). An analysis of the relative rates in six detectors finds sin(2)2 theta(13)= 0.089 +/- 0.010(stat.)+/- 0.005(syst.) in a three-neutrino framework.

A measurement of the energy dependence of antineutrino disappearance at the Daya Bay reactor neutrino experiment is reported. Electron antineutrinos (${\overline{\nu }}_e$) from six $2.9{\mathrm{GW}}_{\mathrm{th}}$ reactors were detected with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls. Using 217 days of data, 41 589 (203 809 and 92 912) antineutrino candidates were detected in the far hall (near halls). An improved measurement of the oscillation amplitude ${\sin }^{2}2{\theta }_{13}=0.090_{-0.009}^{+0.008}$ and the first direct measurement of the ${\overline{\nu }}_e$ mass-squared difference $|\mathrm{\Delta }{m}_{ee}^2|=(2.59_{-0.20}^{+0.19})\times {10}^{-3}{\mathrm{e}\mathrm{V}}^2$ is obtained using the observed ${\overline{\nu }}_e$ rates and energy spectra in a three-neutrino framework. This value of $|\mathrm{\Delta }{m}_{ee}^2|$ is consistent with $|\mathrm{\Delta }{m}_{\mu \mu }^2|$ measured by muon neutrino disappearance, supporting the three-flavor oscillation model.

A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of ${\overline{\nu }}_e$’s. Comparison of the ${\overline{\nu }}_e$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim 1500–1950\mathrm{m}$) relative to detectors near the reactors ($\sim 350–600\mathrm{m}$) allowed a precise measurement of ${\overline{\nu }}_e$ disappearance. More than 2.5 million ${\overline{\nu }}_e$ inverse beta-decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011–July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012–July, 2015). The ${\overline{\nu }}_e$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949\pm 0.002(\text{stat})\pm 0.002(\text{syst})$. The energy dependence of ${\overline{\nu }}_e$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle ${\sin }^{2}2{\theta }_{13}=0.0841\pm 0.0027(\text{stat})\pm 0.0019(\text{syst})$ and the effective neutrino mass-squared difference of $|\mathrm{\Delta }{m}_{\mathrm{ee}}^2|=(2.50\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$. Analysis using the exact three-flavor probability found $\mathrm{\Delta }{m}_{32}^2=(2.45\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$ assuming the normal neutrino mass hierarchy and $\mathrm{\Delta }{m}_{32}^2=(-2.56\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$ for the inverted hierarchy.