Geant4 simulations of the influence of contamination and roughness of the detector surface on background spectra in CRESST

CRESST is an experiment for the direct detection of dark matter, capable of detecting nuclear recoils down to 10 eV, which results in an impressive sensitivity for sub-GeV dark matter particles. For a better understanding of the measured background a background model is developed. The background components are considered via Geant4 simulations. At the current state, the CRESST background model only considers bulk contaminations and treats all detector surfaces as perfect plains. This contribution presents potential effects of a surface contamination with radiogenic nuclides, in combination with the influence of the crystals surface roughness. Nuclide decays near the crystal surface may lead to partial energy deposition inside the detector, potentially causing MeV energy events to influence the background in the keV energy range. Since default Geant4 is not capable of simulating a rough surface, a new extension for simulating a rough surface is developed and the impact of different roughness configurations is studied.