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

TL;DR

This paper reports a precise measurement of electron antineutrino oscillation parameters using nearly 4 million events over 1958 days at Daya Bay, with improved calibration and background reduction techniques.

Contribution

It provides the most accurate measurement of  and  parameters using extensive data and advanced calibration, reducing uncertainties compared to previous studies.

Findings

 = 0.0856 b1 0.0029

 mass-squared difference  = (2.471^{+0.068}_{-0.070}) imes 10^{-3} eV^2

Enhanced calibration and background analysis improved measurement precision.

Abstract

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