Abstract
The ATLAS Level-1 Calorimeter Trigger usesreduced-granularity information from all the ATLAS calorimeters tosearch for high transverse-energy electrons, photons, τ leptons andjets, as well as high missing and total transverse energy. Thecalorimeter trigger electronics has a fixed latency of about 1 μs,using programmable custom-built digital electronics. This paperdescribes the Calorimeter Trigger hardware, as installed in the ATLASelectronics cavern.
Highlights
The ATLAS detector at the CERN Large Hadron Collider (LHC) is one of the largest and most complex pieces of scientific apparatus ever built
The number of hits for each threshold set is summed up to a maximum of seven over the entire detector excluding the forward calorimeters. (A programmable option to include the forward calorimeters in the overall jet trigger is available.) These crate sums are done by one Common Merger Modules (CMMs) in each of the two Jet/Energy-sum Processor (JEP) crates, and one of these acts as ‘system’ CMM
Extra logic in the jet ‘system’ CMM calculates an approximation to the total transverse energy in jets, ETJ, by multiplying the multiplicity of jets exceeding each threshold by an energy value close to that of the threshold
Summary
The ATLAS detector at the CERN Large Hadron Collider (LHC) is one of the largest and most complex pieces of scientific apparatus ever built. The ATLAS trigger system must make an irreversible, online selection of a tiny fraction of collisions within a very short time. The Level-1 Trigger (L1) provides the first and largest step of that selection, and delivers its decision within a fixed time of less than 2.5 μs. A comprehensive overview of the ATLAS detector is given in [1]. The present paper gives a fuller description of the Level-1 Calorimeter Trigger (L1Calo), which is a major component of. At the time of writing these papers, both the detector and the LHC machine were nearing completion. Future papers will describe the operation, software, commissioning and performance of the trigger
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