Commissioning and Alignment of the ATLAS Inner Detector using Cosmic Data

The ATLAS experiment is one of the two general purpose detectors at the LHC at CERN. ATLAS is equipped with a charged particle tracking system built on three sub-detectors, which provide high precision measurements made from a high detector granularity. The pixel and microstrip sub-detectors, which use the silicon technology, are complemented with the transition radiation tracker. The ATLAS detector is operational since 2008 and more than ten million cosmic tracks crossing the Inner Detector have been collected in 2008 and 2009. These data are used for the commissioning of the experiment. The alignment of the Inner Detector tracking system was performed using the 2008 cosmic data. The tracking performance obtained using this alignment is approaching the one obtained using Monte Carlo simulated with perfectly aligned geometry. The effect of systematic misalignments on physics measurements is being studied.