The CMS Muon System and Its Performance in the CMS Cosmic Challenge

The CMS Muon System exploits three different detection technologies in both the central and forward regions, in order to provide a good muon identification and efficient event selection via a multi-level trigger. In summer 2006 the CMS solenoid has been switched on for the first time, generating successfully the designed magnetic field of B = 4 T. During this period also a slice of the CMS detector was operational (the "CMS Cosmic Challenge") including a subset of detectors from all three muon subsystems along with the muon hardware alignment. A dedicated CMS cosmic muon trigger had to be set-up, which was based on the Level-1 trigger inputs from the muon subsystems. The CMS subsystems were integrated in the central DAQ, detector control and data quality monitoring. Cosmic data were taken in different trigger configurations in order to study the behavior of muon detectors in the magnetic field, combined detector operations and trigger synchronization. The recorded data are used to study alignment with tracks, to verify and tune the reconstruction software. The layout and status of the CMS muon system is presented and results of the recent cosmic challenge data taking are discussed.