Improved estimate of the cross section for inverse beta decay

Abstract

Inverse beta decay (IBD) is the dominant mechanism of antineutrino scattering at energies below a few tens of MeV. Its cross section is currently considered to be known with uncertainty of a fraction of percent. Here I point out that in the existing cross-section calculations the vector part of the hadronic current is not conserved, although its conservation is invoked to express the vector form factors by their electromagnetic counterparts. I obtain the IBD cross section in the most general case, with six contributing form factors, and then use theoretical arguments and experimental constraints to reduce their number. Ensuring conservation of the vector current leads to the results which converges to previous calculations at energies of several MeV but is appreciably lower near the reaction threshold. These findings suggest that the current estimate of the flux of geologically produced antineutrinos may be underestimated. The proposed search for light sterile neutrinos using a 144Ce-144Pr source is predicted to collect a lower event rate and to observe a spectral distortion independent of the distance from the source. In reactor-neutrino experiments, the predicted event rate is reduced-diminishing the size of the reported anomaly- A nd the positron spectra are altered.