Speaker
Description
The all-silicon design of the tracking system of the CMS experiment provided excellent resolution for charged tracks and an efficient tagging of jets during Run1 and Run2 of LHC. CMS upgraded and installed the pixel detector during the shutdown in the beginning of 2017. The position and orientation of tracker, consisting of 15148 silicon strip and 1856 silicon pixel modules needed to be determined with a precision of a few micrometers. The alignment also needs to be quickly recalculated each time the state of the CMS magnet is changed between 0T and 3.8T. We present the results of the CMS tracker alignment, which were derived purely from reconstructed tracks of the collisions and cosmic rays data. The geometries are finally carefully validated with data-driven methods. The monitored quantities include the basic track quantities for tracks from both collisions and cosmic muons and physics observables. We also want to share the valuable experiences and lessons learnt from 2017 commissioning, like how we constrain the weak modes of the alignment algorithm, and how the track-based alignment adjusts for the pixel radiation effects.
