Speaker
Description
Understanding the magnitude and features of the highly precise IBD antineutrino spectra published by the Daya Bay, NEOS, and RENO collaboration have been a challenging and rewarding intellectual quest. With respect to the Huber-Mueller model, these spectra show an overall 5% overprediction in the total yield, known as the Reactor Antineutrino Anomaly (RAA), and an underprediction in the 4-6 MeV range, known colloquially as ‘the bump’. The RAA origin has been traced to a normalization issue in the 235U electron spectrum measurement, while we suspect that ‘the bump’ is due to an efficiency issue in the magnetic spectrograph used to measure those electron spectra. We should also note that the assumption of allowed shapes in the conversion method has been called into question.
Summation calculations, also known as ab-initio calculations, although very helpful to trace down antineutrino production, have not been particularly successful either. The reason is the incomplete data available in the nuclear databases for the very short-lived fission products responsible for the IBD spectrum. Until recently, the precise description of decay heat measurements was the only other application that required the same type of data, even though the decay heat standards are less precise than the above mentioned IBD spectra.
In the last year, two research projects started to make their results public, indicating that (a) the allowed shape assumptions are most likely valid, and (b) some of the relevant fission yields may be larger than assumed. In this contribution we review the latest data and methods available, perhaps proposing how to complete the puzzle since we can begin to foresee the shape of the last few missing pieces.
Acknowledgement: This work was supported in part by the U.S. Department of Energy Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02-98CH10886.