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Aligning the CMS muon chambers with the muon alignment system during an extended cosmic ray run
The alignment system for the muon spectrometer of the CMS detector comprises three
independent subsystems of optical and analog position sensors. It aligns muon chambers with respect
to each other and to the central silicon tracker. System commissioning at full magnetic field
began in 2008 during an extended cosmic ray run. The system succeeded in tracking muon detector
movements of up to 18mm and rotations of several milliradians under magnetic forces. Depending
on coordinate and subsystem, the system achieved chamber alignment precisions of 140â350 Âľm
and 30â200 Âľrad, close to the precision requirements of the experiment. Systematic errors on
absolute positions are estimated to be 340â590 Âľm based on comparisons with independent photogrammetry
measurements
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