Performance of the fast ATLAS tracking simulation (FATRAS) and the ATLAS fast calorimeter simulation (FastCaloSim) with single particles

Many physics and performance studies with the ATLAS detector at the Large Hadron Collider require very large samples of simulated events, and producing these using the full Geant4 detector simulation is highly CPU intensive. Often, a very detailed detector simulation is not needed, and in these cases fast simulation tools can be used. In ATLAS two complementary fast simulation programs have been developed. The Fast ATLAS Track Simulation (Fatras) is a program developed for fast simulation of the ATLAS tracking systems, whilst the ATLAS Fast Calorimter Simulation (FastCaloSim) provides fast simulation of the calorimeter systems. Both these programs may be interfaced to the standard ATLAS digitization and reconstruction software. This note presents comparisons of the performance of fully reconstructed tracks simulated using Fatras to tracks simulated using the full Geant4 simulation, and a comparison of the performance of fully reconstructed topoclusters simulated using FastCaloSim compared to the full Geant4 simulation