CMS Tracker Alignment

This page explains how to measure module position and orientation of modules in the CMS tracker. If you are unfamiliar with what the CMS experiments mission is and what the tracker does, please take the tour.

Why alignment?
Mathematical model
Alignment algorithms
Alignment results

Why alignment?

Why do we need to measure position and orientation of the modules? Why didn't we just put the modules where they belong, and basta! One needs to know the position of the pixels and strips in space with a precision of a few micrometer to reach the precision necessary for the physics measurements. (A hair has a diameter of roughly 50 micrometer). If we do not know the strip position with this precision, the decay length measurement is deteriorated and the momentum resolution of the tracker gets worse, and a lot of tax payers money is wasted. We definitely do not want that. The tracker is a large device (more than five meters long, and two meters in diameter), Specially constructed tools and measurement devices have been used to place the modules as precisely as possible. However, a relative precision of 0.1‰ can be reached. This means: The largest structures, which are of about one meter size, can be placed with a precision of several hundred micrometer in the tracker.

  IN WORK

Mathematical model Alignment algorithms Alignment results

Author: Martin.Weber@cern.ch Last modified: Wed Aug 18 14:51:11 2010