Commissioning and Operation of the ATLAS Pixel Detector

In December 2009 the ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a center-of-mass energy of 900 GeV, and in March 2010 at the unprecedented energy of 7 TeV. The ATLAS Pixel Detector is the innermost detector of the ATLAS experiment at the Large Hadron Collider at CERN. It consists of 1744 silicon sensors equipped with approximately 80 million 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. This allowed to optimize the operating parameters of the system, and to qualify the detector with physics data from cosmic muons. After the commissioning phase the Pixel Detector arrived to the first LHC pp collisions run with very good records: 97.5 % of the pixels are operational. Noise occupancy and hit efficiency exceed the design specifications. The alignment is close enough to the ideal one to allow good track reconstruction and invariant mass determination. In this talk, a review of the commissioning and of the first operational experience with 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 commissioning 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.