Muon-Induced Background Study for an Argon-Based Long Baseline Neutrino Experiment

TL;DR

This study assesses muon-induced backgrounds, including neutrons and isotopes, for an argon-based neutrino experiment at SURF, using simulations and analytic models to evaluate production rates at different depths.

Contribution

It provides a comprehensive evaluation of muon-induced backgrounds using both Monte Carlo simulations and analytic models, specifically for the SURF underground facility.

Findings

Muon-induced $^{40}$Cl production rates match between simulations and models.

Background levels are significant at depths less than 4.0 km.w.e.

Depth-dependent background parametrization was developed and validated.

Abstract

We evaluated rates of transversing muons, muon-induced fast neutrons, and production of $^{40}$Cl and other cosmogenically produced nuclei that pose as potential sources of background to the physics program proposed for an argon-based long baseline neutrino experiment at the Sanford Underground Research Facility (SURF). The Geant4 simulations were carried out with muons and muon-induced neutrons for both 800 ft (0.712 km.w.e.) and 4850 ft levels (4.3 km.w.e.). We developed analytic models to independently calculate the $^{40}$Cl production using the measured muon fluxes at different levels of the Homestake mine. The muon induced $^{40}$Cl production rates through stopped muon capture and the muon-induced neutrons and protons via (n,p) and (p,n) reactions were evaluated. We find that the Monte Carlo simulated production rates of $^{40}$Cl agree well with the predictions from analytic models. A depth-dependent parametrization was developed and benchmarked to the direct analytic models. We conclude that the muon-induced processes will result in large backgrounds to the physics proposed for an argon-based long baseline neutrino experiment at a depth of less than 4.0 km.w.e.