Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos in the SK-Gd experiment

TL;DR

This paper reports the first measurement of the atmospheric neutrino-oxygen neutral-current quasielastic cross section using the SK-Gd detector, showing results consistent with theoretical models and previous measurements, and improving neutron tagging with gadolinium.

Contribution

First measurement of the atmospheric neutrino-oxygen NCQE cross section in SK-Gd, utilizing gadolinium to enhance neutron detection and comparing different nucleon-nucleus interaction models.

Findings

Measured cross section: 0.74 ± 0.22 (stat.) +0.85/-0.15 (syst.) × 10^{-38} cm^2/oxygen.

Results are consistent with theoretical flux-averaged cross sections and previous SK measurements.

Binary Cascade and Liege Intranuclear Cascade models fit data better than Bertini Cascade.

Abstract

We report the first measurement of the atmospheric neutrino-oxygen neutral-current quasielastic (NCQE) cross section in the gadolinium-loaded Super-Kamiokande (SK) water Cherenkov detector. In June 2020, SK began a new experimental phase, named SK-Gd, by loading 0.011% by mass of gadolinium into the ultrapure water of the SK detector. The introduction of gadolinium to ultrapure water has the effect of improving the neutron-tagging efficiency. Using a 552.2 day data set from August 2020 to June 2022, we measure the NCQE cross section to be 0.74 $\pm$ 0.22(stat.) $^{+0.85}_{-0.15}$ (syst.) $\times$ 10$^{-38}$ cm$^{2}$/oxygen in the energy range from 160 MeV to 10 GeV, which is consistent with the atmospheric neutrino-flux-averaged theoretical NCQE cross section and the measurement in the SK pure-water phase within the uncertainties. Furthermore, we compare the models of the nucleon-nucleus interactions in water and find that the Binary Cascade model and the Liege Intranuclear Cascade model provide a somewhat better fit to the observed data than the Bertini Cascade model. Since the atmospheric neutrino-oxygen NCQE reactions are one of the main backgrounds in the search for diffuse supernova neutrino background (DSNB), these new results will contribute to future studies - and the potential discovery - of the DSNB in SK.