Validation of Geant4 electromagnetic and hadronic processes in the BaBar detector

BABAR was the first large experiment to use the Geant4 toolkit to build its simulation code. The production version of the simulation has been running since July 2001 and has so far produced 7/spl times/10/sup 9/ fully reconstructed events. Extensive validations of the simulation continue to be performed by comparing the simulated results in various BABAR subdetectors to data. The most stringent test is the examination of electromagnetic shower shapes in the electromagnetic calorimeter (EMC). Agreement of these shower shapes with data represent an important confirmation of both the geometry and material composition of the BABAR detector and of the validity of the Geant4 standard electromagnetic processes invoked by the simulation. As important, but more difficult to test, is the validity of Geant4 hadronic processes. This study led to the choice of the best-performing hadronic model from three available in the Geant4 toolkit. A brief description of the BABAR detector and a summary of the Geant4 physics processes used to simulate it are presented here. Validation plots comparing actual shower shapes with the simulation, and comparing predicted secondary particle distributions with data are shown.