Measurement of electron antineutrino oscillation with 1958 days of operation at Daya Bay

Abstract

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor $\overline{\hat{I}}{½}_e$ inverse beta decay candidates observed over 1958 days of data collection. The installation of a Flash-ADC 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 ${}^9$Li and ${}^8$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 $\overline{\hat{I}}{½}_e$ rates and energy spectra among detectors yields ${\sin }^{2}2\hat{I}{¸}_{13}=0.0856\pm 0.0029$ and $\hat{I}”m_{32}^2=(2.471_{-0.070}^{+0.068})\times 10^{-3}{\mathrm{eV}}^2$ assuming the normal hierarchy, and $\hat{I}”m_{32}^2=-(2.575_{-0.070}^{+0.068})\times 10^{-3}{\mathrm{eV}}^2$ assuming the inverted hierarchy.

6 pages, 4 figures, and 1 table. v4: the published version