Top: distribution of $\Delta xy\vert_{y=0}$ for SPD only, before and after alignment Bottom: distribution $\Delta xy\vert_{y=0}$ for track segments reconstructed in the upper and lower parts of SPD+SSD layers;each track segment is required to have four assigned points; SSD survey and Millepede alignment corrections are applied. In both cases,the distributions are produced from the sample of events used to obtain the alignment corrections. | ![](https://alice-publications.web.cern.ch/sites/default/files/papers/3907/hdxy0_spd_300609_bw-26967.png ) ![](https://alice-publications.web.cern.ch/sites/default/files/papers/3907/hdxy0_spdssd_bw-26968.png ) |