The Final U-235 Reactor Antineutrino Spectrum Result from PROSPECT-I

PROSPECT, the Precision Reactor Oscillation and SPECTrum Experiment, is a short-baseline reactor-based neutrino experiment aiming to make a precision measurement of reactor antineutrino energy spectra and model-independently search for eV-scale sterile neutrinos. The experiment collected over 50,000 neutrino interactions over the course of five reactor-on cycles at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory in 2018 using the PROSPECT-I detector. This data collection was impacted by a gradually increasing number of in-operative PMTs. Here we report on new analysis methods that use single-PMT segments for background rejection and time period subdivision to better utilize double-PMT segments. Combined, these methods yield an increase in the statistical power of the data by about a factor of two. This talk will present the final PROSPECT-I U-235 antineutrino spectrum result, which requires a multi-period unfolding to account for variations in detector response, and interpretation in the context of the 'Reactor Spectrum Anomaly'.