Neutron tagging can greatly reduce spallation backgrounds in Super-Kamiokande
Obada Nairat (Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA); John F. Beacom (Department of Astronomy, Ohio State University, Columbus, Ohio 43210, USA, Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA); Shirley Weishi Li (Department of Physics and Astronomy, University of California, Irvine, California 92697, USA)
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.
