Reevaluating reactor antineutrino spectra with new measurements of the ratio between ${}^{235}$U and ${}^{239}$Pu ${\hat{I}}^2$ spectra

Abstract

We report a reanalysis of the reactor antineutrino energy spectra based on the new relative measurements of the ratio $R={}^e{S}_5{/}^e{S}_9$ between cumulative ${\hat{I}}^2$ spectra from ${}^{235}$U and ${}^{239}$Pu, performed at a research reactor in National Research Centre Kurchatov Institute (KI). A discrepancy with the ${\hat{I}}^2$ spectra measured at Institut Laue-Langevin (ILL) was observed, indicating a steady excess of the ILL ratio by the factor of $1.054\pm 0.002$. We find a value of the ratio between inverse beta decay cross section per fission for ${}^{235}$U and ${}^{239}$Pu: ${(}^5\ddot{I}{ƒ}_f{/}^9\ddot{I}{ƒ}_f{)}_{KI}=1.45\pm 0.03$, and then we reevaluate the converted antineutrino spectra for ${}^{235}$U and ${}^{238}$U. We conclude that the new predictions are consistent with the results of Daya Bay and STEREO experiments.

Added more details on the KI experiment. Corrected the error budget for U-238 in Table 1. Results and conclusions unchanged