The Possible Origin and Implications of the Shoulder in Reactor Neutrino Spectra

Understand

We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments.

• We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra.
• In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from $^{238}$U.
• We consider several possible origins of the shoulder, and find possible explanations.