Precise Determination of the U-235 Reactor Antineutrino Cross Section per Fission

We consider the possibility that the reactor antineutrino anomaly is due to a miscalculation of one or more of the ${}^{235}\text{U}$, ${}^{238}\text{U}$, ${}^{239}\text{Pu}$, and ${}^{241}\text{Pu}$ reactor antineutrino fluxes. From the fit of the data we obtain the precise determination $\sigma_{f,235} = ( 6.33 \pm 0.08 ) \times 10^{-43} , $\text{cm}$^2 / $\text{fission}$$ofthe$^{235}$\text{U}$$ cross section per fission, which is more precise than the calculated value and differs from it by $2.2\sigma$. The cross sections per fission of the other fluxes have large uncertainties and in practice their values are undetermined by the fit. We conclude that it is very likely that at least the calculation of the ${}^{235}\text{U}$ flux must be revised.