Comprehensive Measurement of the Reactor Antineutrino Spectrum and Flux at Daya Bay

TL;DR

This paper presents the most precise measurements to date of reactor antineutrino spectra and fluxes at Daya Bay, revealing discrepancies with existing theoretical models and providing critical data for neutrino physics research.

Contribution

It provides the first high-precision measurements of antineutrino spectra and fluxes from all reactor fissile isotopes, including specific isotopes, with uncertainties as low as 1.3%.

Findings

Measured antineutrino fluxes agree with KI and SM2023 models.

Observed spectrum disagrees with all current models.

Achieved the best precision in reactor antineutrino measurements to date.

Abstract

This Letter reports the precise measurement of reactor antineutrino spectrum and flux based on the full data set of 4.7 million inverse-beta-decay (IBD) candidates collected at Daya Bay near detectors. Expressed in terms of the IBD yield per fission, the antineutrino spectra from all reactor fissile isotopes and the specific $\mathrm{^{235}U}$ and $\mathrm{^{239}Pu}$ isotopes are measured with 1.3$\%$, 3$\%$ and 8$\%$ uncertainties respectively near the 3 MeV spectrum peak in reconstructed energy, reaching the best precision in the world. The total antineutrino flux and isotopic $\mathrm{^{235}U}$ and $\mathrm{^{239}Pu}$ fluxes are precisely measured to be $5.84\pm0.07$, $6.16\pm0.12$ and $4.16\pm0.21$ in units of $10^{-43} \mathrm{cm^2/fission}$. These measurements are compared with the Huber-Mueller (HM) model, the reevaluated conversion model based on the Kurchatov Institute (KI) measurement and the latest Summation Model (SM2023). The Daya Bay flux shows good consistency with KI and SM2023 models, but disagrees with HM model. The Daya Bay spectrum, however, disagrees with all model predictions.