Performance of the ATLAS Muon Spectrometer During the Commissioning

The ATLAS detector has been operated for several months. Its very large Muon Spectrometer includes four different technology chamber types. It should provide muon trigger up to pseudo-rapidity of 2.4 and track reconstruction with a nominal standalone momentum resolution around 10% for particles of 1 TeV. The Muon system, while still in completion, has undergone an intense program of commissioning, ranging from understanding the status of each single chamber to study the performance of the whole system. The data source, besides a few days with LHC single beam, mainly relied on cosmic rays. Several preliminary results relevant to the muon trigger and reconstruction performance will be analyzed.