# Improved Determination of the $^{235}\text{U}$ and $^{239}\text{Pu}$ Reactor Antineutrino Cross Sections per Fission

## TL;DR

This paper refines measurements of reactor antineutrino cross sections for $^{235}$U and $^{239}$Pu, suggesting potential revisions to flux models could address the reactor antineutrino anomaly.

## Contribution

It provides improved experimental determinations of key antineutrino cross sections per fission, combining data to reduce uncertainties and challenge existing theoretical predictions.

## Key findings

- Measured $\sigma_{f,235}$ and $\sigma_{f,239}$ with improved precision.
- Deviations from theoretical values suggest possible flux re-evaluation.
- Indicates larger uncertainties in other isotopes could impact flux models.

## Abstract

We present the results of a combined fit of the reactor antineutrino rates and the Daya Bay measurement of $\sigma_{f,235}$ and $\sigma_{f,239}$. The combined fit leads to a better determination of the two cross sections per fission: $\sigma_{f,235} = 6.29 \pm 0.08$ and $\sigma_{f,239} = 4.24 \pm 0.21 $ in units of $10^{-43} \, \text{cm}^2 / \text{fission}$, with respective uncertainties of about $1.2\%$ and $4.9\%$. Since the respective deviations from the theoretical cross sections per fission are $2.5\sigma$ and $0.7\sigma$, we conclude that, if the reactor antineutrino anomaly is not due to active-sterile neutrino oscillations, it is likely that it can be solved with a revaluation of the $^{235}\text{U}$ reactor antineutrino flux. However, the $^{238}\text{U}$, $^{239}\text{Pu}$, and $^{241}\text{Pu}$ fluxes, which have larger uncertainties, could also be significantly different from the theoretical predictions.