The ATLAS detector digitization project for 2009 data taking

The ATLAS digitization project is steered by a top-level Python digitization package which ensures uniform and consistent configuration across the sub-detectors. The properties of the digitization algorithms were tuned to reproduce the detector response seen in lab tests, test beam data and cosmic ray running. Dead channels and noise rates are read from database tables to reproduce conditions seen in a particular run. The digits are then persistified as Raw Data Objects with or without intermediate simulation of the exact data acquisition format depending on the detector type. Emphasis is put on the description of the digitization project configuration, its flexibility in handling events for processing and in the global detector configuration. Other options available, including detector noise simulation, random number service, metadata and details of pile-up background events to be overlaid, are also described. The LHC beam bunch spacing is also configurable, as well as the number of bunch crossings to overlay and the default detector conditions (including noisy channels, dead electronics associated with each detector layout). Cavern background calculation, beam halo and beam gas treatment and pile-up with real data are also part of this report.