A fast parametrization of electromagnetic and hadronic calorimeter showers

Fast parametrizations of electromagnetic and hadronic calorimeter showers have been extracted from a full GEANT simulation of single particles in the ATLAS calorimeters. The response and the resolution have been determined for photons and charged pions over the momentum range from 200 MeV/c up to 200 GeV/c and for the pseudorapidity range |eta|<4.9. Within the parametrization model, the shower energy is deposited into a matrix of calorimeter cells with a granularity of \Delta eta x \Delta phi = 0.1 x 0.1 including event by event fluctuations and correlations among the different cells. In the longitudinal shower direction only the sharing between the electromagnetic and the hadronic calorimeters is simulated. The parametrization model and tests of its performance are presented.