The ATLAS Level-1 Central Trigger

The ATLAS Level-1 trigger system is responsible for reducing the anticipated LHC collision rate from 40 MHz to less than 100 kHz. This Level-1 selection counts jet, tau/hadron, electron/photon and muon candidates, with additional triggers for missing and total energy. The results are used by the Level-1 Central Trigger to form a Level-1 Accept decision. This decision, along with timing signals, is sent to the sub-detectors from the Level-1 Central trigger, while summary information is passed into the higher levels of the trigger system. The performance of the Central Trigger during the first collisions will be shown. This includes details of how the trigger information, along with dead-time rates, are monitored and logged by the online system for physics analysis, data quality assurance and operational debugging. Also presented are the software tools used to efficiently display the relevant information in the control room in a way useful for shifters and experts.