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Revisiting reactor antineutrino 5 MeV bump with C13 neutral-current interaction

Pouya Bakhti1,*, Min-Gwa Park1,2,†, Meshkat Rajaee1,‡, Chang Sub Shin3,4,5,§, and Seodong Shin1,4,∥

  • *Contact author: pouya_bakhti@jbnu.ac.kr
  • †Contact author: mgpark@jbnu.ac.kr
  • ‡Contact author: meshkat@jbnu.ac.kr
  • §Contact author: csshin@cnu.ac.kr
  • ∥Contact author: sshin@jbnu.ac.kr
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Phys. Rev. D 112, 055046 – Published 29 September, 2025

DOI: https://doi.org/10.1103/s64c-l1p9

Abstract

For the first time, we comprehensively examine the potential of a neutral-current interaction of reactor neutrino with C13 emitting a 3.685 MeV photon to identify the origin of the 5 MeV bump in reactor antineutrino spectra observed through the inverse beta decay process. This anomaly may be due to new physics, reactor antineutrino flux inaccuracies, or inverse beta decay systematics. The 3.685 MeV photon released during the deexcitation of C*13 to its ground state is observable in liquid scintillator detectors. Remarkably, we confirm the powerfulness of our proposal by completely ruling out a new physics scenario explaining the bump from the existing NEOS data. We also 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 measure the cross section precisely enough to distinguish the expected bump and the theoretical flux models via our channel. Additionally, we propose a novel method to track the time evolution of reactor isotopes by analyzing the C13 signal, which yields critical insights into the contributions of U235 and Pu239 to the bump, acting as a robust tool.

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Phys. Rev. D 112, 055046– Published 29 September, 2025
  • Received 1 July 2024
  • Accepted 2 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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