PROSPECT-I Absolute Antineutrino Flux Measurement

The Precision Reactor Oscillation and SPECTrum (PROSPECT) experiment is a short-baseline reactor experiment operating in close proximity to the High Flux Isotope Reactor (HFIR), an 85MW highly-enriched uranium reactor at Oak Ridge National Laboratory (ORNL). The primary goal of PROSPECT is to observe evidence of short-baseline sterile neutrino fluctuation through measurement of antineutrino energy spectra. The first phase of PROSPECT (PROSPECT-I) gathered data from 2018 to 2019 at HFIR using a 6Li-doped liquid scintillator detector divided into 154 segments, each able to detect neutrinos emitted via inverse beta decay (IBD) events. In the process of inverse beta decay, the emitted positron captures on the liquid scintillator, releasing light detected by photomultiplier tubes (PMTs) on each end of each segment. PROSPECT-I is able to provide extremely precise measurements of the 235-uranium antineutrino spectrum as well as improved limits on eV-scale sterile neutrino fluctuations due to its high signal-to-background ratio. A standing goal of PROSPECT is to measure the absolute neutrino spectrum; a task that requires precise evaluation of several detector characteristics to minimise uncertainty, such as the proton density of the scintillator and the efficiency of the detector. The former can be precisely determined using quantitative nuclear magnetic resonance (qNMR) techniques, while detector efficiency is characterised by detailed detector simulations and calibration source studies.