Abstract
Given the harsh detector environment produced by collisions of high energy protons at the LHC, events with muons in the final state are an important signature for many physics analyses. The ATLAS experiment employs a multi-level trigger architecture that selects the events in three sequential steps of increasing complexity and accuracy. The Level 1 trigger is implemented with custom-built hardware to reduce the event rate (in 2012) from 20 MHz to 70 kHz. Then the software-based higher level triggers refine the trigger decisions reducing the output rate down to several 100 Hz. The performance of the muon trigger is presented as determined with pp collision data collected in 2012 at a centre-of-mass energy of 8 TeV.
Highlights
Muons in the final state are distinctive signatures of many physics studies performed at the LHC, such as the observation and measurements of a Higgs boson, searches for new phenomena, as well as the measurements of Standard Model (SM) processes
The precise determination of the muon trigger performance of the ATLAS detector [1] at the LHC is essential for muon-related physics analyses
At Event Filter (EF), there is an additional algorithm which starts with inner detector (ID) tracks around the L1 RoI and extrapolates those to the muon detectors to collect the data from the muon spectrometer (MS) either to form a combined muon candidate or to just tag the ID track as a muon
Summary
Muons in the final state are distinctive signatures of many physics studies performed at the LHC, such as the observation and measurements of a Higgs boson, searches for new phenomena, as well as the measurements of Standard Model (SM) processes. The ATLAS muon trigger system has been designed to select muons in a wide momentum range with high efficiency. The precise determination of the muon trigger performance of the ATLAS detector [1] at the LHC is essential for muon-related physics analyses. To address a wide variety of physics topics, the ATLAS experiment deployed several muon triggers. The deflection of the muon trajectories in the magnetic field is measured using hits in three layers of precision drift tube (MDT) chambers for |η| < 2.0. Three layers of resistive plate chambers (RPC) in the barrel region (|η| < 1.05) and three layers of thin gap chambers (TGC) in the endcap regions (1.05 < |η| < 2.4) provide the L1 muon trigger. The momenta and positions of the muons are measured independently in the ID and in the MS, and the ID-MS combination provides the most precise measurement of the muon kinematics, as well as the lowest fake rate
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