Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water

TL;DR

This paper reports a precise measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium-loaded water, improving background understanding for neutrino and rare event searches.

Contribution

The study provides the first measurement of neutron yield in Super-Kamiokande after gadolinium loading, enhancing background modeling for neutrino experiments.

Findings

Neutron yield measured as (2.76 ± 0.02 (stat.) ± 0.19 (syst.)) × 10^{-4} μ^{-1} g^{-1} cm^{2}.

Measurement conducted at an average muon energy of 259 GeV.

Gadolinium loading improved neutron detection efficiency.

Abstract

Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic showers due to spallation in water, producing neutrons and radioactive isotopes. Those are a major background source for studies of MeV-scale neutrinos and searches for rare events. Since 2020, gadolinium was introduced in 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 $(2.76 \pm 0.02\,\mathrm{(stat.) \pm 0.19\,\mathrm{(syst.)}}) \times 10^{-4}\,\mu^{-1} \mathrm{g^{-1} cm^{2}}$ at 259 GeV of average muon energy at the Super-Kamiokande detector.