Abstract
The all-silicon design of the CMS tracker poses new challenges in aligning the system with more than 15,000 independent modules. For optimal track-parameter resolution, the position and orientation of its modules need to be determined with a precision of better than few dozens of micrometres. Starting with the survey measurements and corrections provided by the hardware alignment system, the ultimate precision can be achieved with data from the silicon modules traversed in situ by charged particles. Several implementations of statistical algorithms allow to solve the optimization problem with the required accuracy in manageable time. Survey measurements and experience with the hardware alignment system are described as well as the selection of data samples used for track-based alignment and results from Monte Carlo studies. First CMS tracker alignment analysis results with cosmic track data are given.
Highlights
The CMS trackerThe CMS silicon tracker, comprising an inner pixel and an outer strip detector, is the largest silicon detector ever built with a total active area of about 200 m2
The all-silicon design of the CMS tracker poses new challenges in aligning the system with more than 15,000 independent modules
The CMS silicon tracker, comprising an inner pixel and an outer strip detector, is the largest silicon detector ever built with a total active area of about 200 m2
Summary
The CMS silicon tracker, comprising an inner pixel and an outer strip detector, is the largest silicon detector ever built with a total active area of about 200 m2. The pixel detector consists of 1,440 modules with a total of 66 million channels and is composed of three 53 cm long barrel layers closed by two end cap disks of 30 cm diameter on either side. It is enclosed by the strip detector which is itself divided into an inner barrel/end cap structure, Tracker Inner Barrel (TIB) and Tracker Inner Disks (TID), and an outer structure consisting of an outer barrel (TOB) and two end caps (TEC). In the TEC, modules are placed in ring structures on wedge shaped “petals” which are themselves attached on both sides of nine large disks staggered along z
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