The Atlas Muon Spectrometer

The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is expected to record its first data from proton-proton collisions in autumn 2009. Its muon spectrometer is designed to achieve a momentum resolution of better than 10% at 1 TeV. The spectrometer consists of a system of three superconducting air-core toroid magnets and is instrumented with three layers of Monitored Drift Tube chambers (Cathode Strip Chambers in the extreme forward region) as precision detectors. Resistive Plate Chambers in the barrel and Thin Gap Chambers in the endcap regions provide a dedicated fast trigger system. In summer 2008, during the start-up phase of the LHC, the first events from single beams were recorded with the fully functional ATLAS detector. Previous and subsequent data taking with cosmic rays yielded a data set of several 100 Million events with and without magnetic field. We will report on the current status and our experience with the muon precision tracking and trigger chambers, the level-1 trigger, and the spectrometer alignment. The global performance of the muon system will be discussed and first results from combined studies with other sub-detectors will be presented. The readiness of the ATLAS muon spectrometer for first collisions will be demonstrated.