New Methods and Simulations for Cosmogenic Induced Spallation Removal in Super-Kamiokande-IV

TL;DR

This paper introduces new techniques for identifying and removing muon-induced spallation backgrounds in Super-Kamiokande-IV, improving solar neutrino detection efficiency and validating simulation models with FLUKA for future enhancements.

Contribution

It presents novel methods for locating muon-induced showers and effectively rejecting spallation backgrounds, along with the first detailed simulation of hadronic interactions at SK using FLUKA.

Findings

Signal efficiency increased by 12.6% in solar neutrino analysis.

First FLUKA-based spallation simulation at SK shows good agreement with data.

Simulation enables future optimization of background removal with gadolinium detection.

Abstract

Radioactivity induced by cosmic muon spallation is a dominant source of backgrounds for $\mathcal{O}(10)~$MeV neutrino interactions in water Cherenkov detectors. In particular, it is crucial to reduce backgrounds to measure the solar neutrino spectrum and find neutrino interactions from distant supernovae. In this paper we introduce new techniques to locate muon-induced hadronic showers and efficiently reject spallation backgrounds. Applying these techniques to the solar neutrino analysis with an exposure of $2790\times22.5$~kton.day increases the signal efficiency by $12.6\%$, approximately corresponding to an additional year of detector running. Furthermore, we present the first spallation simulation at SK, where we model hadronic interactions using FLUKA. The agreement between the isotope yields and shower pattern in this simulation and in the data gives confidence in the accuracy of this simulation, and thus opens the door to use it to optimize muon spallation removal in new data with gadolinium-enhanced neutron capture detection.