Measurement of reactor antineutrino flux and spectrum at RENO

The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos ν_¯e from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966 094 116 111 ν_{¯ e} candidate events with a background fraction of 2.39% (5.13%), acquired in the near (far) detector, from August 2011 to March 2020. The inverse beta decay (IBD) yield is measured as (5.852 ±0.094 )×10^-43 cm²/fission , corresponding to 0.941 ±0.015 of the prediction by the Huber and Mueller (HM) model. A reactor ν_¯e spectrum is obtained by unfolding a measured IBD prompt spectrum. The obtained neutrino spectrum shows a clear excess around 6 MeV relative to the HM prediction. The obtained reactor ν_¯e spectrum will be useful for understanding unknown neutrino properties and reactor models. The observed discrepancies suggest the next round of precision measurements and modification of the current reactor ν_¯e models.