Speaker
Description
Summary 500 words
The ATLAS trigger system is responsible for reducing the event rate, from the design bunch-crossing rate of 40 MHz, to an average recording rate of 200 Hz, by selecting signal-like events out of the extremely large background. The ATLAS trigger is designed in three levels. The first-level (L1) is implemented in custom-built electronics, the two levels of the high level trigger (HLT) are software triggers executed on large computing farms. The first-level trigger is comprised of calorimeter, muon and forward triggers to identify event features, such as missing transverse energy, as well as candidate electrons, photons, jets and muons. These inputs are used by the L1 Central Trigger to for
a L1 Accept (L1A) decision. L1A and timing information is sent to all sub-detectors. Summary information is sent to the subsequent levels of the trigger system.
We will demonstrate that the ATLAS trigger performed smoothly throughout 2010 and 2011, showing the evolution with the increasing LHC luminosity (10^{32}-10^{33} cm^{-1} s^{-1}) in
order to maintain a high selection efficiency. A large part of the talk will be devoted to recent improvements of the L1 trigger system.
