Measurement of the U-235 antineutrino energy spectrum with PROSPECT*

PROSPECT is a short-baseline experiment observing reactor antineutrinos from the 85MW highly-enriched uranium High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Positioned 7.9m from HFIR, the segmented liquid scintillator detector was designed to search for eV-scale sterile neutrino oscillations and make a precision measurement of the U-235 antineutrino energy spectrum. Using 40 days of reactor-on data, PROSPECT has detected >31,000 antineutrinos, resulting in the world-leading measurement of the U-235 spectrum. PROSPECT disfavors U-235 as the sole isotope responsible for the spectral discrepancy observed by nuclear power reactor experiments at ~3σ.