Alignment of the ATLAS Inner Detector tracking system

The ATLAS Inner Detector (ID) consists of two silicon subsystems, the Pixel detector and the Semiconductor Tracker (SCT), complemented by the Transition Radiation Tracker (TRT) composed of drift tubes. After the assembly of the detector, the position of the individual modules is known with much worse accuracy than their intrinsic resolution. Therefore a track-based alignment procedure has to be applied. The baseline goal is to determine the position and orientation of the modules with such precision that the track parameters’ determination is not worsened by more than 20% with respect to that expected from the perfectly aligned detector. This is crucial for efficient track reconstruction and precise momentum measurement and vertex reconstruction. The alignment of the ID requires the determination of its almost 36,000 degrees of freedom(DoF) with high accuracy. Thus the demanded precision for the alignment of the silicon sensors is below 10 micrometer.The implementation of the track based alignment with the ATLAS software framework unifies different alignment approaches and allows the alignment of all tracking subsystems together. The results of the alignment using real data recorded during the LHC start up run in 2009 plus the recent 7TeV data collected during 2010 run will be presented.