The alignment of the CMS Silicon Tracker

The complex system of the CMS all-silicon Tracker, with 15148 silicon strip and 1440 silicon pixel modules, requires sophisticated alignment procedures. In order to achieve an optimal trackparameter resolution, the position and orientation of its modules need to be determined with a precision of few micrometers. We present results of the alignment of the full Tracker, in its final position, used for the reconstruction of the first collisions recorded by the CMS experiment. The aligned geometry is based on the analysis of several million reconstructed tracks recorded during the commissioning of the CMS experiment, both with cosmic rays and with the first proton-proton collisions. The geometry has been systematically monitored in the different periods of operation of the CMS detector. The results have been validated by several data-driven studies. The influence of remaining 2 -invariant detector movements is estimated by investigating the sensitivity of the alignment procedure to some correlated detector distortions and testing their influence on physics analysis like the B-fraction measurement in J/ events.