Abstract
The ATLAS experiment at CERN's Large Hadron Collider (LHC) deploys a three-level processing scheme for the trigger system. The development of fast trigger algorithms and the design of topological selections are the main challenges to allow for a large program of physics analyses. In the following, two of the ATLAS trigger signatures are described: the muon and the tau triggers. The structure of the three levels of these two trigger signatures are explained in detail as well as their performance during the first three years of operation.
Highlights
ATLAS is one of the two multipurpose experiments at the Large Hadron Collider (LHC)
The high pT thresholds have 5-10% lower efficiency than the low pT thresholds in the barrel region: this is due to the fact that the latter require the coincidence of only two layers of muon chambers
The ATLAS detector has a three level trigger system, which allows to reduce the incoming rate of 20 MHz LHC collisions to ∼400Hz of recorded data
Summary
ATLAS is one of the two multipurpose experiments at the LHC. Physics goals include the search for the Higgs boson and new physics beyond the Standard Model. The frequency of a process like H → ZZ → μμμμ is extremely rare: once in 1013 pp interactions (at 14 TeV) Another reason is linked to resources: both computing time and data storage limits are challenging. It is important to have a trigger system which can select efficiently events with many muons Another example is the decay of the Higgs boson in tau pairs, H → τhadτlep. In this case the signature is the presence of an hadronic tau and a lepton, e.g. a muon. The interesting event is overlaid with 25 additional interactions In such a busy environment several trigger levels are needed to be able to exploit tracking information at the trigger selection
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