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Super-Kamiokande’s spallation backgrounds—the delayed beta decays of nuclides following cosmic-ray muons—are nearly all produced by the small fraction of muons with hadronic showers. We show that these hadronic showers also produce neutrons; their captures can be detected with high efficiency due to the recent addition of dissolved gadolinium to Super-Kamiokande. We show that new cuts based on the neutron tagging of showers could reduce spallation backgrounds by a factor of at least four beyond present cuts. With further work, this could lead to a near elimination of detector backgrounds above about 6 MeV, which would significantly improve the sensitivity of Super-Kamiokande. These findings heighten the importance of adding gadolinium to Hyper-Kamiokande, which is at a shallower depth. Further, a similar approach could be used in other detectors, for example, the JUNO liquid-scintillator detector, which is also at a shallower depth. Published by the American Physical Society2025
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Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water
Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic showers due to spallation in water, producing neutrons and radioactive isotopes. These are a major background source for studies of MeV-scale neutrinos and searches for rare events. In 2020, gadolinium was introduced into the ultra-pure water in the Super-Kamiokande detector to improve the detection efficiency of neutrons. In this study, the cosmogenic neutron yield was measured using data acquired during the period after the gadolinium loading. The yield was found to be ð2.76 0.02ðstatÞ 0.19ðsystÞÞ × 10−4 μ−1 g−1 cm2 at an average muon energy 259 GeV at the Super-Kamiokande detector.
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- Award ID(s):
- 2013073
- PAR ID:
- 10439806
- Date Published:
- Journal Name:
- Physical review D Particles and fields
- Volume:
- 107
- ISSN:
- 0556-2821
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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