Muon-induced background study for an argon-based long baseline neutrino experiment

We evaluated rates of transversing muons, muon-induced fast neutrons, and production of Cl-40 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, Homestake Mine, in Lead, South Dakota. The Geant4 simulations were carried out with muons and muon-induced neutrons for both the 800 ft level (0.712 km w.e.) and 4850 ft level (4.3 km w.e.). We developed analytic models to independently calculate the Cl-40 production using the measured muon fluxes at different levels of the Homestake Mine. The muon induced Cl-40 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 Cl-40 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.