The ATLAS level-1 central trigger processor core module (CTP_CORE)

ATLAS is a detector at CERN´s Large Hadron Collider where bunches of protons in counter-rotating beams will cross every 25 ns producing, on average, about 25 collisions for a total interaction rate of 1 GHz. A three-level trigger system selects bunch crossings potentially containing interesting processes. The level-1 trigger, implemented in electronics and firmware, makes an initial selection in under 2.5 μs with an output rate of less than 100 kHz. A key element of this is the core module of the central trigger processor which combines trigger information from the calorimeter and muon trigger processors to make the final level-1 accept decision in under 75 ns. The event-selection algorithm used by the core module is based on lists of selection criteria (trigger menu) and is implemented in fully programmable look-up tables and content-addressable memories. In addition to the event selection, the core module generates dead-time in order to limit the frequency of level-1 accepts to a rate that the sub-detector front-end electronics can support. The core module further provides trigger-summary information to the level-2 trigger and to the data acquisition system. The design of the core module is presented, and results from recent laboratory tests and from tests with the calorimeter and muon trigger processors connected to detectors in a particle beam are shown.