Speaker
Diego Casadei
(New York University (US))
Description
The ATLAS trigger has been used very successfully to collect collision
data during 2009-2011 LHC running at centre of mass energies between
900 GeV and 7 TeV. The three-level trigger system reduces the event
rate from the design bunch-crossing rate of 40 MHz to an average
recording rate of about 300 Hz. The first level uses custom
electronics to reject most background collisions, in less than 2.5 us,
using information from the calorimeter and muon detectors. The upper
two trigger levels are software-based triggers. The trigger system
selects events by identifying signatures of muon, electron, photon,
tau lepton, jet, and B meson candidates, as well as using global event
signatures, such as missing transverse energy. We give an overview of
the performance of these trigger selections based on extensive online
running during the 2011 LHC run and discuss issues encountered during
2011 operations. Distributions of key selection variables are shown
calculated at the different trigger levels and are compared with
offline reconstruction. Trigger efficiencies with respect to offline
reconstructed signals are shown and compared to simulation,
illustrating a very good level of understanding of the detector and
trigger performance. We describe how the trigger has evolved with
increasing LHC luminosity coping with pileup conditions close to LHC
design luminosity.
Primary author
Dr
Brian Petersen
(CERN)
Co-author
Diego Casadei
(New York University (US))
