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

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor νₑ 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 νₑ rates and energy spectra among detectors yields sin²2θ₁₃=0.0856±0.0029 and Δm₃₂²=(2.471_-0.070+0.068)×10^-3 eV² assuming the normal hierarchy, and Δm₃₂²=-(2.575_-0.070+0.068)×10^-3 eV² assuming the inverted hierarchy.