Alignment of the CMS Silicon Strip Tracker during stand-alone Commissioning

TL;DR

This paper reports on the initial alignment of the CMS Silicon Strip Tracker using cosmic ray data, survey, and laser systems, validating alignment methods and structural stability under different conditions at CERN.

Contribution

First alignment of CMS Silicon Tracker modules using cosmic tracks, survey, and laser data, validating methods and assessing structural stability during commissioning.

Findings

Alignment precision comparable to simulated residuals

Validation of survey and laser system performance

Structural stability under temperature variations

Abstract

The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15C to -15C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) microns in the outer (inner) part of the barrel.