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 $\overline{\nu}{e}$ 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.

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

The study presented in this paper details a comprehensive measurement of electron antineutrino oscillation, obtained through the extensive data gathered by the Daya Bay Reactor Neutrino Experiment over 1958 days. The experimental design focuses on understanding the oscillation parameter θ₁₃ and the effective mass-squared difference, Δm²ₑₑ, by observing reactor antineutrinos. This essay will summarize the main findings, methodology, and implications of this research within the domain of neutrino physics.

The Daya Bay experiment utilizes eight identical antineutrino detectors (ADs) spread across three experimental halls, strategically placed to monitor antineutrinos produced by six reactor cores. The detection method is centered on the inverse beta decay (IBD) reaction, characterized by specific prompt and delayed signal events. The setup and methodology are detailed, with significant considerations made to improve energy calibration and reduce uncertainties from various sources.

Key improvements facilitated the precise measurement of the oscillation parameters. These include advancements in detector calibration—specifically the installation of a Flash-ADC system—and a specialized calibration campaign that enhanced the energy resolution and minimized systematic discrepancies across detectors. This effort reduced the uncertainties related to the absolute energy calibration and cosmogenic background levels in near detectors. The calibration efforts achieved less than 0.5% uncertainty for visible energies greater than 2 MeV.

Numerical results reveal values of $\sin^2 2\theta_{13} = 0.0856 \pm 0.0029$ and $$\Delta m^2_{32} = (2.471^{+0.068}_{-0.070}) \times 10^{-3}$$ eV² assuming a normal hierarchy, with notable precision in these measurements. The study's statistical strength is derived from nearly four million observed IBD candidates, and the systematic improvements contribute substantially to the accuracy of these results.

The implications of these precise measurements extend both theoretically and practically. The research bolsters the understanding of neutrino oscillation phenomena, providing insights into fundamental particle physics and aiding further exploration into the characteristics of neutrino mass and mixing. Such advancements could inform future experimental designs and theoretical models, shaping the next steps in neutrino research and potentially impacting fields reliant on nuclear physics and astrophysics.

As the precision of Δm²₃₂ measured here is comparable to and corroborates results from accelerator-based experiments like MINOS, NOvA, and T2K, this convergence of findings consolidates the oscillation parameters, further establishing them in the neutrino physics framework.

Future endeavors in neutrino research may focus on extending the precision achieved here to other related measurements, integrating these findings into broader investigatory scopes such as exploring CP-violating effects or expanding the detection methodologies. Continued data accumulation and methodological refinement at existing and forthcoming facilities like Daya Bay are paramount for advancing the collective understanding of neutrino properties, guiding theoretical insights and experimental confirmations in particle physics.