Bridging the gap between Monte Carlo simulations and measurements of the LISA Pathfinder test-mass charging for LISA

Cubic gold-platinum free-falling test masses (TMs) constitute the mirrors of future LISA and LISA-like interferometers for low-frequency gravitational wave detection in space. High-energy particles Galactic solar origin charge TMs thus induce spurious electrostatic magnetic forces that limit sensitivity these interferometers. Prelaunch Monte Carlo simulations TM charging were carried out Pathfinder (LPF) mission, was planned to instrumentation. Measurements compared during mission operations. The measured net agreed with simulation estimates, while noise three four times higher. We aim bridge gap between LPF observations. New due both FLUKA/LEI toolkit. This allowed propagating low-energy electrons down a few electronvolt. These improved agree observations gathered operations within statistical errors. induced by cosmic rays is about one thousand charges per second. value increases tens thousands second energetic particle events. Similar results are expected charging.