Performance of the ATLAS muon trigger in 2011

Events with muons in the final state are an impor- tant signature for many physics analyses in the harsh detector environment produced by collisions of high energy protons. The ATLAS experiment employs a multi-level trigger architecture that selects events in three sequential steps of increasing com- plexity and accuracy. The Level 1 trigger is implemented with custom built hardware to reduce the event rate from 40 MHz to 75 kHz. The software based higher level triggers refine the trigger decisions reducing the output rate down to the order of 100 Hz. This note presents the performance of the muon trigger evaluated with proton-proton collision data collected in 2011 at a centre-of-mass energy of 7 TeV.