Neutron Tagging Can Greatly Reduce Spallation Backgrounds in Super-Kamiokande

TL;DR

This paper demonstrates that neutron tagging via gadolinium enhances background reduction in Super-Kamiokande, potentially improving sensitivity and informing future detector designs like Hyper-Kamiokande and JUNO.

Contribution

It introduces a neutron tagging method that significantly reduces spallation backgrounds, leveraging gadolinium detection to improve neutrino observation sensitivity.

Findings

Neutron captures can be detected efficiently with gadolinium.

Neutron tagging can reduce spallation backgrounds by at least a factor of four.

Potential for near-elimination of backgrounds above 6 MeV.

Abstract

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.