Accurate Measurement of the Electron Antineutrino Yield of U-235 Fissions from the STEREO Experiment with 119 Days of Reactor-On Data

We report a measurement of the antineutrino rate from the fission of U-235 with the STEREO detector using 119 days of reactor turned on. Considering several corrections, which are presented in detail, we achieve accurate results and report the most precise single measurement at reactors with highly enriched U-235 fuel. We measure an IBD cross-section per fission of $\sigma_f$ = (6.34 $\pm$ 0.06 [stat] $\pm$ 0.15 [sys] $\pm$ 0.15 [model]) $\cdot$ 10${}^{-43}$ cm${}^{2}$/fission and observe a rate deficit of (5.2 $\pm$ 0.8 [stat] $\pm$ 2.3 [sys] $\pm$ 2.3 [model])% compared to the model. Here, the first and second uncertainties are experimental and the third is from the model. We confirm the deficit between the world average and the model.