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New spallation background rejection techniques to greatly improve the solar neutrino sensitivity of JUNO

Obada Nairat1,2,*, John F. Beacom1,2,3,†, and Shirley Weishi Li4,‡

  • *Contact author: nairat.2@osu.edu
  • †Contact author: beacom.7@osu.edu
  • ‡Contact author: shirley.li@uci.edu
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Phys. Rev. D 114, 043047 – Published 19 August, 2026

DOI: https://doi.org/10.1103/zpyz-7vsq

Abstract

While the potential of the Jiangmen Underground Neutrino Observatory (JUNO) to measure solar neutrinos is known, realizing this potential requires new techniques to reduce detector backgrounds. One of the most serious backgrounds is due to the beta decays of unstable nuclei produced through muon breakup (spallation) of nuclei. This background is much more significant in JUNO compared to Super-Kamiokande due to JUNO’s shallower depth and its lack of directional information. We present the first detailed theoretical calculations of spallation backgrounds in JUNO, showing the underlying physical processes and new ways to cut backgrounds while preserving signals. A key point is showing the importance of neutron tagging to identify hadronic showers, which are rare but produce almost all of the dangerous isotopes. With our new techniques, JUNO will be able to reduce dead time (signal loss) by a factor of about 4.5 and to reduce the running time needed to meet sensitivity goals by a factor of 2. This will give JUNO greatly improved sensitivity to B8 and hep solar neutrinos, as we will explore in a separate paper.

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See Also

Toward First Detection of the Solar Mikheyev-Smirnov-Wolfenstein Transition with JUNO

Obada Nairat, John F. Beacom, Kevin J. Kelly, and Shirley Weishi Li
Phys. Rev. Lett. 137, 081801 (2026)

Article Text

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Phys. Rev. D 114, 043047– Published 19 August, 2026
  • Received 30 October 2025
  • Accepted 14 July 2026
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