Evolution of reactor flux and spectrum at Daya Bay and the implications on the Reactor Antineutrino Anomaly

PPRC Seminars
David Martinez (Illinois Inst Tech, USA)
Teppei Katori
October 27th, 2017 at 13:30
GO Jones Room 410

The reactor antineutrino anomaly (RAA) has been puzzling reactor neutrino physics community since 2011. The RAA refers to the deficit of electron antineutrinos detected by reactor neutrino experiments compared with the number of electron antineutrinos predicted by state of the art reactor models. The Daya Bay experiment has utilized eight functionally identical underground detectors to sample reactor antineutrino fluxes from three pairs of nuclear reactors in South China, accruing the largest reactor antineutrino sample to date. This talk will summarize Daya Bay’s most recent result, which presents observations of correlations between reactor core fuel evolution and changes in the detected reactor antineutrino flux and energy spectrum. A 10σ variation in IBD yield was found to be energy-dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the linear variation with respect to the fuel content in the IBD spectrum show general agreement with predictions from recent reactor models, the measured linear variation with respect to the fuel content in the total IBD yield disagrees with recent predictions. This discrepancy indicates that an overall deficit in measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes 235U, 239Pu, 238U, and 241Pu. A 7.8% discrepancy between the observed and predicted 235U yield suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.