Speaker
Dr
Sinead Farrington
(University of Oxford)
Description
This paper will give an overview of the ATLAS trigger design and its innovative features. It will
describe the valuable experience gained in running the trigger reconstruction and event selection in the fastchanging
environment of the detector commissioning during 2008. It will also include a description of the
trigger selection menu and its 2009 deployment plan from first collisions to the nominal luminosity.
ATLAS is one of the two general-purpose detectors at the Large Hadron Collider (LHC). The trigger
system needs to efficiently reject a large rate of background events and still select potentially interesting ones
with high efficiency. After a first level trigger implemented in custom electronics, the trigger event selection
is made by the High Level Trigger (HLT) system, implemented in software. To reduce the processing time to
manageable levels, the HLT uses seeded, step-wise and fast selection algorithms, aiming at the earliest
possible rejection of background events. The ATLAS trigger event selection is based on the reconstruction of
potentially interesting physical objects like electrons, muons, jets, etc.
The recent LHC startup and short single-beam run provided the first test of the trigger system against
real data. Following this period, ATLAS continued to collect cosmic-ray events for detector alignment and
calibration purposes. Both running periods provided very important data to commission the trigger
reconstruction and selection algorithms. Profiting from this experience and taking into account the ATLAS
first year physics goals, we are preparing a trigger selection menu including several tracking, muon-finding
and calorimetry algorithms. Using Monte Carlo simulated data, we are evaluating the impact of the trigger
menu on physics performance and rate.
Primary author
Dr
Sinead Farrington
(University of Oxford)
