Reactor Antineutrino Directionality Measurement with the PROSPECT-I Detector

The PROSPECT-I detector has several features that enable measurement of the direction of a compact neutrino source. In this paper, a detailed report on the directional measurements made on electron antineutrinos emitted from the High Flux Isotope Reactor is presented. With an estimated true neutrino (reactor to detector) direction of \(\phi = 40.8\unicode{xB0} \pm 0.7\unicode{xB0}\) and \(\theta = 98.6\unicode{xB0} \pm 0.4\unicode{xB0}\), the PROSPECT-I detector is able to reconstruct an average neutrino direction of \(\phi = 39.4\unicode{xB0} \pm 2.9\unicode{xB0}\) and \(\theta = 97.6\unicode{xB0} \pm 1.6\unicode{xB0}\). This measurement is made with approximately 48000 Inverse Beta Decay signal events and is the most precise directional reconstruction of reactor antineutrinos to date.