A Study Of The Anti-Neutrino Flux From The Reactors Of The Daya Bay Experiment

An improved measurement of electron anti-neutrino flux at the Daya Bay Reactor Neutrino Experiment using six 2.9-GWth nuclear power reactors at multiple baselines?350 m?1900 m?is presented.At present,more than 2.5 million inverse beta-decay?IBD?interactions have been acquired,which is the world's largest reactor??_edataset ever.A series of calibrations was carried out at Daya Bay.A gamma calibration allows a sub-percent precision in the establishment of the energy model.A high-activity neutron calibration leads to a stringent constraint on the background caused by the neutron sources in the calibration systems to a level of 0.26±0.12per detector per day.Based on an elaborate neutron calibration campaign in late 2016 and an improved analysis approach,the IBD detection efficiency is determined to be 80.25%±0.95%.The experimental normalization of the anti-neutrino flux with respect to the Huber-Mueller model is found to be R=0.950±0.014,consistent with the observations from past short-baseline experiments.In particular,a fuel separated flux measurement indicates that the anti-neutrino yield from²³⁵U is 7.5%lower than the model prediction and is likely to be the main cause of the deviation from unity in the experimental normalization.