Beam test of the ATLAS level-1 calorimeter trigger system

The level-1 calorimeter trigger consists of a preprocessor (PP), a cluster processor (CP), and a jet/energy-sum processor (JEP). The CP and JEP receive digitised trigger-tower data from the preprocessor and produce regions-of-interest (RoIs) and trigger multiplicities. The latter are sent in real time to the central trigger processor (CTP) where the level-1 decision is made. On receipt of a level-1 accept, readout driver modules (RODs) provide intermediate results to the data acquisition (DAQ) system for monitoring and diagnostic purposes. RoI information is sent to the RoI builder (RoIB) to help reduce the amount of data required for the level-2 trigger. The level-1 calorimeter trigger system at the test beam consisted of 1 preprocessor module, 1 cluster processor module, 1 jet/energy module and 2 common merger modules. Calorimeter energies were successfully handled throughout the chain and trigger objects sent to the CTP. Level-1 accepts were successfully produced and used to drive the readout path. Online diagnostics were made using 4 RODs. Energy histograms were plotted and the integrity of data between the different modules was checked. All ATLAS detectors in the test beam were able to build full events based on triggers delivered by the calorimeter trigger system.