Simulating Geomagnetic Effects on Muons and Muon-Induced Subshowers from EASs for the EUSO-SPB2 Mission

The Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2) was launched on May 13, 2023 from Wanaka, New Zealand and reached a planned float altitude of 33 km before a leak in the balloon forced an early flight termination. The Cherenkov Telescope (CT), when pointed above Earth’s limb (650 km away), observed the optical Cherenkov signals from near-horizontal extensive air shower (EAS) candidates developing in Earth’s upper atmosphere. This horizontal configuration is unique in that it could possibly observe atmospheric muons deflecting in the geomagnetic field. The thin upper atmosphere absorbs a small fraction of muons’ energy (approximately 40 MeV/km at 15 km altitude) and the decay constant of a 100 GeV muon corresponds to approximately 620 km. Since existing simulations have difficulties modeling shower development in horizontal geometries, we present a simulation framework to model the Cherenkov signal produced by muons and their subshowers in near-horizontal EASs as they interact in the geomagnetic field. Our simulation emulates the expected Cherenkov signal from muons in the geometry of the CT and identifies characteristics of this signal attributed to muon deflections within the geomagnetic field. This research may also be applied to investigate whether detected Cherenkov signals are muon-induced showers and whether magnetic field deflections enable muons to create Cherenkov light appearing to arrive from below Earth’s limb, resembling neutrino/tau-induced showers.