Performance of the ATLAS Trigger with Proton Collisions at the LHC

THE ATLAS COLL. , J. BAINES; MARIA TERESA DOVA ET AL.

Paris

Conferencia; 35th International Conference of High Energy Physics; 2010

LHC running at centre-of-mass energies of 900GeV, 2.36TeV, and7TeV. The trigger system Reduces the event rate, from the design bunch-crossing rate of 40MHz, to an average recording rate of 200Hz. The ATLAS trigger is composed of three levels. The first (L1) uses custom electronics to reject most background collisions, in less than 2.5µs, using information from the calorimeter and muon detectors. The upper two trigger levels, known collectively as the High Level Trigger (HLT), are software-based triggers. As well as triggers using global event features, Such as missing transverse energy, there are selections based on identifying candidate muons, electrons, photons, tau leptons or jets. We describe how the trigger has evolved withi ncreasing LHC Luminosity and give a brief overview of plans forf orthcoming LHC running.