Performance of the CMS silicon Tracker at LHC

The CMS all-silicon Tracker, comprising 16588 modules covering an area of more than 200m², needs to be precisely calibrated and aligned in order to correctly interpret and reconstruct the events recorded from the detector, ensuring that the performance fully meets the physics research program of the CMS experiment. The performance has been carefully studied since the start of data taking: the noise of the detector, the data integrity, the S/N ratio, the hit resolution and efficiency have been all investigated with time. In 2010 the Tracker has been successfully aligned using tracks from cosmic rays and pp-collisions, following the time dependent movements of its innermost pixel layers. Ultimate local precision is now achieved by the determination of sensor curvatures, challenging the algorithms to determine about 200000 parameters. Remaining alignment uncertainties are dominated by systematic effects that are controlled by adding further information, such as constraints from resonance decays.