Comparison between full and fast simulation of the ATLAS detector for the channel H/A->ttbar

This note describes the comparison between full and fast simulation of the ATLAS detector for events with Higgs boson decaying to ttbar. A good agreement between the two simulation packages is found for the acceptance of the kinematic cuts and in the reconstructed quantities involved in them. The top and Higgs mass resoltuions are in reasonable agreement, with full simulation predicting resolutions which are 10-20% worse than those from the fast simulation.