Commissioning and performance of the ATLAS Inner Detector with the first beam and cosmic data

The ATLAS experiment at the CERN Large Hadron Collider (LHC) started data-taking in Autumn 2008 with the inauguration of the LHC. The Inner Detector is a tracking system for charged particles based on three technologies: silicon pixels, silicon micro-strips and drift tubes. The detector was commissioned and calibrated in the ATLAS cavern. Cosmic muons data are used for timing the different components of the system, measuring detector performance on particles and cross-checking the calibration results. Cosmic ray data serve also to align the detector prior to the LHC start up, exercising the alignment procedure to be repeated during the acceleratorʹs operation. Tracking performance after this early alignment is suitable for initial LHC collisions.