Abstract
The all-silicon design of the tracking system of the CMS experiment provides excellent measurements of charged-particle tracks and an efficient tagging of jets. Conditions of the CMS tracker changed repeatedly during the 2015/2016 shutdown and the 2016 data-taking period. Still the true position and orientation of each of the 15 148 silicon strip and 1440 silicon pixel modules need to be known with high precision for all intervals. The alignment constants also need to be promptly re-adjusted each time the state of the CMS magnet is changed between 0T and 3.8 T. Latest Run-II results of the CMS tracker alignment and resolution performance are presented, which are obtained using several millions of reconstructed tracks from collision and cosmic-ray data of 2016. The geometries and the resulting performance of physics observables are carefully validated. In addition to the offline alignment, an online procedure has been put in place which continuously monitors movements of the pixel high-level structures and triggers updates of the alignment constants if certain thresholds are exceeded.
Highlights
Change of position parameters Change of track parameters Change of other residuals
® moving module by −r means Change of position parameters Change of track parameters Change of other residuals
® Cosmic tracks are split at point of closest approach to the interaction region ® Differences in track quantities between the two parts indicate misalignment ® Derived updated alignment with 0 T cosmic data prior to 2016 data-taking start-up
Summary
® 15 148 silicon strip modules (24 244 sensors) 2D measurements (r φ direction) In some layers: additional modules rotated by 100 mrad. ® Difference between real and assumed geometry affects track measurement ® Idea: track-hit residuals r between predicted and measured hit positions as a measure of misalignment real track real geometry. ® Difference between real and assumed geometry affects track measurement ® Idea: track-hit residuals r between predicted and measured hit positions as a measure of misalignment r assumed geometry. ® Idea: track-hit residuals r between predicted and measured hit positions as a measure of misalignment reconstructed track. Change of position (alignment) parameters Change of track parameters Change of other residuals. ® Difference between real and assumed geometry affects track measurement reconstructed track assumed geometry. ® Idea: track-hit residuals r between predicted and measured hit positions as a measure of misalignment. ® moving module by −r means Change of position (alignment) parameters Change of track parameters Change of other residuals
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
