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 $\phi =40.8\text{unicode}xB0\pm 0.7\text{unicode}xB0$ and $\theta =98.6\text{unicode}xB0\pm 0.4\text{unicode}xB0$, the PROSPECT-I detector is able to reconstruct an average neutrino direction of $\phi =39.4\text{unicode}xB0\pm 2.9\text{unicode}xB0$ and $\theta =97.6\text{unicode}xB0\pm 1.6\text{unicode}xB0$. This measurement is made with approximately 48000 Inverse Beta Decay signal events and is the most precise directional reconstruction of reactor antineutrinos to date.