Commissioning and performance of the ATLAS Transition Radiation Tracker with first high energy pp and Pb-Pb collisions at LHC

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three sub-systems of the ATLAS Inner Detector at the Large Hadron Collider at CERN. It consists of close to 300000 thin-wall drift tubes (straws) providing on average 30 two-dimensional space points with 0.12-0.15 mm resolution for charged particle tracks with |η| < 2 and pT > 0.5 GeV. Along with continuous tracking, it provides particle identification capability through the detection of transition radiation X-ray photons generated by high velocity particles in the many polymer fibers or films that fill the spaces between the straws. Custom-built analog and digital electronics is optimized to operate as luminosity increases to the LHC design. In this talk, a review of the commissioning and first operational experience of the TRT detector will be presented. Emphasis will be given to performance studies based on the reconstruction and analysis of LHC collisions. A comparison of the TRT response to two very different center of mass energy collisions (900 GeV and 7000 GeV) will be presented here. In addition, for the first time studies of the response of the TRT detector to the extreme high track density condition occurred during the November 2010 heavy ion LHC running period will be presented here for the first time, giving interesting insight on the expected performance of the TRT gas detector for future LHC proton-proton high luminosity runs. The techniques used are applicable to a wide range of charged particle and soft x-ray detection scenarios.