The beta radioactivity of fission products in nuclear reactors is responsible for their very high production of antineutrinos. In 2011, the revision of the theoretical model of electron/antineutrino conversion revealed a 6% deficit between the predicted antineutrinos and those measured in the vicinity of reactors. Two hypotheses were considered at the time: there were other types of sterile neutrinos whose properties had to be characterised, or the model was imperfect. The SEN group is working on the only alternative model to conversion: the summation method, as well as on experimental measurements to improve its predictivity. The model consists of a careful study of the nuclear decay of the main contributors to the antineutrino emission in the fuel and to sum their contributions. Associated with the TAGS collaboration, the group has so far been able to measure and analyse 15 major nuclei for the prediction of antineutrino spectra. The inclusion of these Pandemonium-corrected nuclei in the calculation of the flux of produced antineutrinos shows a systematic effect: the predicted flux is consistently closer to the measured flux (see figure) and seems to confirm the results of the neutrino experiments regarding the imperfection of the conversion model. The flux discrepancy narrows to 2% with the measurements of flux of the Daya Bay collaboration and the impact of other TAGS nuclei on the model will be assessed soon.

Deficit Antineutrinos Subatechv2

Caption: In 2011 the summation model (Greenwood) then compatible with the conversion model predicted 6% more antineutrinos than measured by Daya Bay (DB). The improvement of the nuclear model in 2012, 2015, 2017 and 2018 thanks to the TAGS data allowed to reduce the gap to 2%. Figure M. Estienne et al. Phys. Rev. Lett. 123 (2019) 022502.