PROSPECT-I Measurement of Absolute Reactor Antineutrino Flux*

The Precision Reactor Oscillation and SPECTrum (PROSPECT) experiment is a short-baseline reactor experiment designed to measure the spectrum of antineutrinos and search for evidence of short baseline sterile neutrino oscillations. From 2018 to 2019, the first-generation detector, PROSPECT-I, took data while located roughly 7 m from the High Flux Isotope Reactor (HFIR), an 85 MW, compact core, highly enriched research reactor at Oak Ridge National Laboratory (ORNL). PROSPECT-I was a segmented ⁶Li-loaded liquid scintillator detector which detected neutrinos via inverse beta decay (IBD) events, by detecting the scintillation light of the IBD positron and other particles produced when the IBD neutron captured on the ⁶Li. PROSPECT-I has demonstrated the highest signal-to-background ratio of any surface antineutrino detector with minimal overburden, placing stringent limits on eV scale sterile neutrino oscillations, setting new direct limits on boosted dark matter models, and providing one of the most precise measurements to date of the ²³⁵U antineutrino spectrum. This talk will present ongoing work by the PROSPECT collaboration towards making an absolute flux measurement of the reactor antineutrinos, and detail ongoing work on measuring the detector’s neutron detection efficiency. A significant focus of this work is calculating inefficiencies caused by the fraction of neutrons capturing on targets other than ⁶Li.