Extending ICARUS's Sensitivity to Hidden Sector Scalars with a Search for Uncontained Dimuon Final States

Abstract

The ICARUS detector is a liquid argon time projection chamber (LArTPC) acting as the far detector in the Short Baseline Neutrino program at Fermilab. Complementing its ability to better constrain neutrino physics, ICARUS is also able to probe any dark sector state present in the exposed flux, that results in a final state of charged Standard Model particles within the active volume of the detector. This work exploits such sensitivity to the Higgs portal scalar (HPS) and heavy QCD axion (ALP, for "axion-like particles") models with a selection for final states with exactly two muons, where at least one of the muons is not contained in the fiducial volume of the detector. The ALPs and HPSs are generated from meson-decay or -mixing in the Neutrinos at the Main Injector (NuMI) beam at Fermilab, propagate to ICARUS, and then decay into the dimuon pair. The work expands on the sensitivity probed by an earlier ICARUS result that selected final states of two fully-contained muons, extending ICARUS’s reach to a higher phase space of dark sector models. The ICARUS detector, HPS and ALP models, simulation pipelines, uncontained dimuon event selection, systematic uncertainties, and strategy for extracting results are discussed.