The L2 trigger for the ATLAS detector at the LHC

A three stage trigger is proposed for the ATLAS detector at the LHC. The first level will use coarse calorimeter and muon chamber information to reduce the data rate from the bunch crossing rate of 40 MHz to 100 kHz. The second level trigger is described here. It will use the full detector granularity to refine the level one thresholds, and make global event decisions to reduce the rate by a further factor of 100. It is envisaged that level two will be based upon commerically available processors and network elements.