부산대학교 도서관

For the first time, we comprehensively examine the potential of neutrino-nucleus neutral current interactions with $^{13}$C to determine the origin of the 5-MeV bump in reactor antineutrino spectra observed through the inverse beta decay (IBD) process. This anomaly may be due to new physics, reactor antineutrino flux inaccuracies, or IBD systematics. The primary signal is the 3.685 MeV photon released during the de-excitation of $^{13}$C$^*$ to its ground state, detectable in various liquid scintillator detectors. This interaction is most common for reactor antineutrinos within the energy range of the 5-MeV bump, providing unique sensitivity to its origins. Remarkably, we confirm the powerfulness of our proposal by completely ruling out a new physics scenario explaining the bump from the existing NEOS data. The main systematic challenge in distinguishing flux models is the accuracy of cross section measurements; thus, minimizing these uncertainties is essential. Hence, we explore the potential of current and forthcoming experiments, including solar neutrino studies at JUNO, pion and muon decay-at-rest experiments at OscSNS, and isotope decay-at-rest studies at Yemilab, to obtain precise cross section measurements. Additionally, we propose a novel method to track the time evolution of reactor isotopes by analyzing the $^{13}$C signal. This technique yields critical insights into the contributions of $^{235}$U and $^{239}$Pu to the observed bump, acting as a robust tool to differentiate between flux models and explore new physics explanations for the 5-MeV bump.
Comment: 12 pages, 6 figures