Alignment of the CMS muon detectors

The CMS Muon system consists of 250 drift tube (DT) chambers in the central region and 468 cathode strip chambers (CSC) in the forward region, complimented by 480 fasts-response resistive plate chambers distributed in both regions for triggering purposes. The muon system provides fast muon trigger, muon identification, and muon trajectory measurements. The performance of the muon system depends on the precise knowledge of the positions and orientations of all its elements within the CMS detector. We present two alignment techniques, track-based and hardware-based. The track-based technique uses muon tracks from pp collision data at the LHC to align the muon system elements relative to the CMS inner silicon tracker. A complimentary hardware-based technique consists of two separate optical systems in the central and forward regions linked by a third system to the inner tracker. The hardware systems are designed to perform well in an environment of large radiation flux and high magnetic field. We discuss the alignment results of the several years of CMS operation, the achieved precision of the alignment techniques and the resulting impact on muon momentum resolution.