nuSpaceSim: a Comprehensive Simulation Package for Optical Cherenkov and Radio Emission from Neutrino-Sourced Extensive Air Showers

nuSpaceSim is an open-source, modular, end-to-end simulation which models the signals produced by upwards moving extensive air showers (EAS) sourced by cosmic neutrinos. The goal of the nuSpaceSim package is to provide the community with a validated and comprehensive computation scheme with which to evaluate the sensitivity of arbitrary experimental geometries (mountain-top, sub-orbital, orbital) and techniques (radio, optical Cherenkov) to diffuse and point source neutrino fluxes above PeV energies via the Earth-skimming technique. nuSpaceSim uses the results of the validated nuPyProp code to model neutrino propagation inside the Earth, which properly accounts for neutrino interactions, charged lepton energy losses and decay, and potential τ →ντ→ τ regeneration. Comparable results from another propagator, based on the nuTauSim code, have also recently been added. nuSpaceSim models all physical processes from Earth emergence to detection to calculate sensitivities, including: the decays of the τ-lepton, the development of the EAS, the generation of the radio and optical Cherenkov signals, the atmospheric propagation of the signal, and the instrumental response. The physics modules of nuSpaceSim can be called independently and for enhanced performance, are written in high-level languages (Fortran, C, C++). For easier interfacing, these functions are wrapped in a vectorized Python scheduler which allows for efficient, multicore, parallel processing, with event-by-event analysis variables kept during simulation. nuSpaceSim is being further developed to model the sensitivity to transient neutrino sources, improve atmospheric models, refine radio and optical modeling from EAS, and include other channels of detection (such as muons sourced from νμ and ντ) and potential backgrounds (above-the-horizon cosmic rays). The current version of nuSpaceSim, v1.2.5, is available using both github and pip via a dedicated HEASARC webpage. In this work, we discuss the software and physics modeling of the nuSpaceSim simulation package.