Performance of the ATLAS Muon Spectrometer and Muon Identification

The large cosmic data samples collected in 2008 and 2009 by the ATLAS experiment have been used to study the performance of the muon spectrometer. Studies of the muon spectrometer performance in terms of tracking efficiency and momentum resolution are presented and provide an update with respect to results recently published. The results are also compared with a recently improved cosmic data simulation. Differences between data and simulation are discussed. The performance of the ATLAS muon identification was studied with an integrated luminosity of 17 nb−1 of LHC proton-proton collision data at a centre of mass energy of 7 TeV. Exploiting the redundancy in the muon identification at detector and reconstruction level, the performance of the identification steps could be checked with data. Results are presented on the scale and resolution of the momentum measurement, the low momentum background, and the prompt muon fraction.