Measurement of the Electron Antineutrino Oscillation with 1958 Days of Operation at Daya Bay

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We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor ${\overline{\ensuremath{\nu}}}_{e}$ inverse $\ensuremath{\beta}$ 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 ${\overline{\ensuremath{\nu}}}_{e}$ rates and energy spectra among detectors yields ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{13}=0.0856\ifmmode\pm\else\textpm\fi{}0.0029$ and $\mathrm{\ensuremath{\Delta}}{m}_{32}^{2}=({2.471}_{\ensuremath{-}0.070}^{+0.068})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$ assuming the normal hierarchy, and $\mathrm{\ensuremath{\Delta}}{m}_{32}^{2}=\ensuremath{-}({2.575}_{\ensuremath{-}0.070}^{+0.068})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$ assuming the inverted hierarchy.

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