Ab initio calculations of reactor antineutrino fluxes with exact lepton wave functions

Abstract

New ab initio calculations of the isotopic reactor antineutrino fluxes are provided with exact numerical calculations of the lepton wave functions, assuming all the decay branches are allowed GT transitions. We illustrate that the analytical Fermi function and finite size effect each could have the largest spectral deviation of O(10%), whereas the effect of their combination could result in spectral deviations at the level of 5%—10%. Meanwhile, we also find that several forms of the extended charge distributions have negligible effects on the spectral variation. Using the state-of-the-art nuclear databases, compared to usual ab initio calculations using the analytical single beta decay spectrum, our new calculation shows sizable but opposite spectral deviations at the level of 2%—4% for the cumulative antineutrino and electron energy spectra which may partially contribute to the observed spectral excess in the high energy antineutrino range. Finally we observe that the bias of analytical beta decay spectrum approximation is rather universal for all the four fissionable isotopes.