Addressing the Reactor Antineutrino Anomaly with a New Detector Array for Fission Fragment Beta-Spectroscopy

Since the discovery of the neutrino in 1956, nuclear reactors have played an important role in understanding the properties of beta decay and probing the nature of the weak interaction. Repeatedly, reactor-based experimental studies of neutrino oscillations have observed a deficit in measured values of antineutrino flux relative to the flux predicted by prominent fissile antineutrino models [7, 2]. Most recently, the Daya Bay experiment reported measured antineutrino flux relative to the number predicted by current models of reactor antineutrino spectra of 0.946 ± 0.022 [10]. Several explanations have been put forward, including the possibility of new physics beyond the standard model (e.g., sterile neutrinos), or deficiencies in current models of 235U fission product beta spectra [19]. This work describes efforts to directly measure the beta spectrum of 92Rb, one of the largest contributors to the aggregate 235U antineutrino spectrum, using a new detector array constructed at Argonne National Laboratory’s CARIBU user facility