The Geant4-based BABAR simulation

The simulation production code for the BABAR experiment is based on the Geant4 toolkit. In a typical e(+)e(-) --> Y(4s) --> B-0(B-0) over bar event, between 30 and 60 tracks are produced in the generator and propagated through the detector, using decay, electromagnetic and hadronic processes provided by the Geant4 toolkit. The material model of the detector is very detailed and a special particle transportation module was developed so that minute features would be sampled in the propagation without sacrificing performance. The propagation phase for such an event requires 3.8 CPU seconds on an 866 MHz processor. Execution speeds for other BABAR event types will also be presented. Validation of simulated events against data from BABAR and other experiments is ongoing, and the results of Monte Carlo/data comparisons will be shown. A discussion of the design of the simulation code and its robustness, how the Geant4 toolkit is used, and ongoing efforts to improve the agreement between data and Monte Carlo will also be presented.