Improved Measurement of the Reactor Antineutrino Flux at Daya Bay

TL;DR

This paper presents a highly precise measurement of reactor antineutrino flux at Daya Bay, reducing uncertainties and confirming a discrepancy with theoretical models, thus advancing neutrino physics understanding.

Contribution

The study achieves a 56% reduction in neutron detection efficiency uncertainty and provides the most precise IBD yield measurement to date.

Findings

Measured IBD yield: (5.91±0.09)×10^{-43} cm^2/fission.

Measured to predicted flux ratio: 0.952±0.014±0.023 for Huber-Mueller model.

Confirms discrepancy between observed flux and theoretical predictions.

Abstract

This work reports a precise measurement of the reactor antineutrino flux using 2.2 million inverse beta decay (IBD) events collected with the Daya Bay near detectors in 1230 days. The dominant uncertainty on the neutron detection efficiency is reduced by 56% with respect to the previous measurement through a comprehensive neutron calibration and detailed data and simulation analysis. The new average IBD yield is determined to be $(5.91\pm0.09)\times10^{-43}~\rm{cm}^2/\rm{fission}$ with total uncertainty improved by 29%. The corresponding mean fission fractions from the four main fission isotopes $^{235}$U, $^{238}$U, $^{239}$Pu, and $^{241}$Pu are 0.564, 0.076, 0.304, and 0.056, respectively. The ratio of measured to predicted antineutrino yield is found to be $0.952\pm0.014\pm0.023$ ($1.001\pm0.015\pm0.027$) for the Huber-Mueller (ILL-Vogel) model, where the first and second uncertainty are experimental and theoretical model uncertainty, respectively. This measurement confirms the discrepancy between the world average of reactor antineutrino flux and the Huber-Mueller model.