Modelling of Compton scattering within the Fast ATLAS Track Simulation

The Fast ATLAS Tracking Simulation (FATRAS) is a computationally efficient tool being developed to simulate the particle interactions within the inner detector of the ATLAS experiment. The development of accurate fast-simulation tools is essential to handling the increased event rates of the upcoming High-Luminosity Large Hadron Collider. This project addresses the lack of Compton scattering modelling in FATRAS by implementing the Klein-Nishina (KN) differential cross-section and developing a parametrised model for the KN total cross-section. The implemented model of Compton scattering demonstrates strong agreement when compared to benchmark Geant4 simulations. Further, a promising parametrisation of the integrated KN cross-section is presented, offering an efficient alternative to direct integration. Future work involves benchmarking the computational performance of the differential cross-section implementation and integrating the total cross-section model into FATRAS.