Options for the ATLAS Level 2 Trigger

The high rate of interactions in future LHC experiments places stringent demands on the trigger and data acquisition systems. The first-level trigger for the ATLAS experiment is based on special-purpose processors designed to reduce the trigger rate from the 40 MHz beam-crossing rate to below 100 kHz. Higher-level triggers are required to reduce the data flow to about 100 MB/s (100 Hz with full data) for permanent storage. Processing for the second-level trigger uses data from regions of interest (RoIs) defined by the first-level trigger, whereas full event data (about 1 MB per event) is used at Level-3. The present paper presents options for the ATLAS Level-2 trigger.