Theory of inverse beta decay for reactor antineutrinos

Abstract

Inverse beta decay (IBD), ${\overline{\nu }}_{e}p\to e^{+}n\left(\gamma \right)$, is the main detection channel for reactor antineutrinos in water- and hydrocarbon-based detectors. As reactor antineutrino experiments now target sub-percent-level sensitivity to oscillation parameters, a precise theoretical description of IBD, including recoil, weak magnetism, nucleon structure, and radiative corrections, becomes essential. In this work, we give a detailed and precise calculation of the total and differential cross sections for radiative IBD, ${\overline{\nu }}_{e}p\to e^{+}n\gamma$. We use a heavy baryon chiral perturbation theory framework, systematically incorporating electroweak, electromagnetic, and strong-interaction corrections. We derive new analytic cross-section expressions, clarify the collinear structure of radiative corrections, and provide a systematic uncertainty analysis. We also discuss phenomenological applications for reactor antineutrino experiments, e.g., JUNO, and neutron decay. Our results enable sub-permille theoretical precision, supporting current and future experiments.

Comments: 57 pages, 12 figures, 1 table; version published in Physical Review D; text in footnote 10 and Introduction to Section 4 clarified; expression 192 added; Section 4.3 extended; minor text and figure corrections; Section 5.4 added; author list extended by authors who contributed to Section 5.4