This Letter reports the first measurement of the oscillation amplitude and frequency of reactor antineutrinos at Daya Bay via neutron capture on hydrogen using 1958 days of data. With over 3.6 million signal candidates, an optimized candidate selection, improved treatment of backgrounds and efficiencies, refined energy calibration, and an energy response model for the capture-on-hydrogen sensitive region, the relative νe rates and energy spectra variation among the near and far detectors gives sin 2 2θ13 = 0.0759 +0.0050 −0.0049 and ∆m 2 32 = (2.72 +0.14 −0.15 )× 10 −3 eV 2 assuming the normal neutrino mass ordering, and ∆m 2 32 = (−2.83 +0.15 −0.14 )×10 −3 eV 2 for the inverted neutrino mass ordering. This estimate of sin 2 2θ13 is consistent with and essentially independent from the one obtained using the capture-on-gadolinium sample at Daya Bay. The combination of these two results yields sin 2 2θ13 = 0.0833 ± 0.0022, which represents an 8% relative improvement in precision regarding the Daya Bay full 3158-day capture-on-gadolinium result.

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The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery ofν e oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of sin 2 2θ 13 and the effective mass splitting ∆m 2 ee . The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

This Letter presents results of a search for the mixing of a sub-eV sterile neutrino with three active neutrinos based on the full data sample of the Daya Bay Reactor Neutrino Experiment, collected during 3158 days of detector operation, which contains 5.55 × 10 6 reactor νe candidates identified as inverse beta-decay interactions followed by neutron-capture on gadolinium. The analysis benefits from a doubling of the statistics of our previous result and from improvements of several important systematic uncertainties. No significant oscillation due to mixing of a sub-eV sterile neutrino with active neutrinos was found. Exclusion limits are set by both Feldman-Cousins and CLs methods. Light sterile neutrino mixing with sin 2 2θ14 ≳ 0.01 can be excluded at 95% confidence level in the region of 0.01 eV 2 ≲ |∆m 2 41 | ≲ 0.1 eV 2 . This result represents the world-leading constraints in the region of 2 × 10 −4 eV 2 ≲ |∆m 2 41 | ≲ 0.2 eV 2 .