The GMT detector alignment in the STAR experiment

The Solenoidal Tracker At RHIC (STAR) uses the Time Projection Chamber (TPC) to perform tracking and particle identification. In order to improve the corrections (such as space charge) and monitor non-static distortions of the TPC, GEM-based chambers (GMT) were installed at eight locations outside the TPC where they will provide optimal sensitivity to the distortions. In order to reach this goal, the ionization clusters were measured by using the ADC signals in each module. The positions of clusters and their deviations from track projections enabled alignment of the GMT modules with respect to TPC to an accuracy ~ 200{\mu}m.