The positions of the nearly twenty-thousand silicon sensors of the CMS central tracking system must be determined with a precision better than their intrinsic resolution in order to provide an optimal reconstruction of charged particle trajectories. The procedure, referred to as the alignment, includes also the adjustment of the orientations and the determination of the deviation from flatness of the sensor surfaces.
Data-driven methods used to carefully align the detector and validate the alignment are presented using CMS Run 2 data, collected from 2016 to 2018. Systematic distortions such as weak modes are discussed, as well as the impact of the variation of the conditions during data taking over time, in particular effects related to radiation damage.
Finally, we illustrate the impact on physics of the recent developments included in the Legacy Reprocessing, which was performed with the aim to greatly improve the physics potential for
precision measurements, such as the reconstruction of the invariant mass spectrum of the dilepton systems.