Measurement of the 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 ν_e inverse β 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 ^9Li and ^8He 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 ν_e rates and energy spectra among detectors yields sin^22θ_(13) = 0.0856±0.0029 and Δm^2_(32)=(2.471^(+0.068)_(−0.070))×10^(-3)  eV^2 assuming the normal hierarchy, and Δm^2_(32) = −(2.575^(+0.068)_(−0.070))×10^(-3)  eV2 assuming the inverted hierarchy.

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