CMS muon alignment: System description and first results

Mar Sobron,P Martinez Ruiz Del Arbol

doi:10.1016/j.nima.2008.08.101

Abstract

The CMS detector has been instrumented with a precise and complex opto-mechanical alignment subsystem that provides a common reference frame between tracker and muon detection systems by means of a net of laser beams. The system allows a continuous and accurate monitoring of the muon chambers positions with respect to the tracker body. Preliminary results of operation during the test of the CMS 4 T solenoid magnet, performed in 2006, are presented. These measurements complement the information provided by the use of survey techniques and the results of alignment algorithms based on muon tracks crossing the detector.

Highlights

For optimal performance of the CMS muon spectrometer [1] over the entire momentum range up to the TeV range, the different muon chambers must be aligned with respect to each other and to the central tracking system to within a few hundred microns in rφ
In what follows we describe the alignment strategy, a brief description of the optical alignment system, and the results from the different measurements sources
Solenoid effects: Magnetic forces generated by the 4T solenoid field lead to displacements and deformations of the return yoke which is at the same time the support structure of the muon chambers

Summary

Introduction

For optimal performance of the CMS muon spectrometer [1] over the entire momentum range up to the TeV range, the different muon chambers must be aligned with respect to each other and to the central tracking system to within a few hundred microns in rφ. After following strict chamber construction specifications, CMS combines precise survey and photogrammetry measurements, measurements from an opto-mechanical system, and the results of alignment algorithms based on muon tracks (both from cosmic rays and from pp collisions) crossing the spectrometer. During the MTCC (Magnet Test and Cosmic Challenge)[2] a third of the optical alignment system was implemented allowing preliminary studies of the detector behavior under the effect of magnetic forces.

Results

Conclusion