The ATLAS trigger system aims at reducing the 40 MHz protons collision event rate to a
manageable event storage
rate of 1 kHz, preserving events with valuable physics
meaning. The Level-1 trigger is the first rate-reducing
step in the ATLAS
trigger system, with an output rate of 100 kHz and decision latency of less
than 2.5 micro
seconds. It is composed of the calorimeter trigger, muon trigger and central trigger processor. During the last
upgrade, a new electronics element was
introduced to Level-1: L1Topo, the Topological Processor System.
make it possible to use detailed realtime information from the Level-1
calorimeter and muon triggers,
processed in individual state of the art FPGA
processors to determine angles between jets and/or leptons
calculate kinematic variables based on lists of selected/sorted objects.
Over hundred VHDL algorithms are
producing trigger outputs to be incorporated
into the central trigger processor.
Such information will be
essential to improve background rejection and
increase the significance of a large spectrum of the ATLAS physics
An overview of the firmware implementation, algorithms performance and their impact over
results will be illustrated.