Commissioning and Operation of the ATLAS Pixel Detector

The ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a centre-of-mass energy of 900 GeV in December 2009, and at the unprecedented energy of 7 TeV in March 2010. The ATLAS Pixel Detector is the innermost detector of the ATLAS experiment at the Large Hadron Collider at CERN. It consists of 1744 n-in-n silicon pixel sensors equipped with approximately 80 M electronic channels, providing typically three measurement points with high resolution for particles emerging from the beam-interaction region, thus allowing to measure particle tracks and secondary vertices with very high precision. Before the start of LHC operations, the completed Pixel Detector was operated for many months under realistic conditions in the ATLAS experimental hall, after installation. This allowed to optimize the operating parameters of the system, and to qualify the detector with physics data from cosmic muons. At the start of LHC, 97.5 % of the pixels were operational, noise occupancy and hit efficiency exceeded the design specifications, the intrinsic spatial resolution and the alignment were close to the ideal ones. In this talk, a review of the commissioning and first operational experience of the Pixel Detector will be presented, including monitoring and calibration procedures, and the timing optimization process, as the detector operation progressed from commissioning with cosmic ray data to commis sioning with collisions and finally to steady-state data taking. In addition, the current status of the Pixel Detector and its response to LHC high energy proton-proton collisions will be presented.