Performance of the ATLAS Transition Radiation Tracker with Cosmic Rays and First High Energy 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 (LHC) at CERN. It consists of close to 300000 thin-wall drift tubes (straws) providing on average 30 two-dimensional space points with 130 μm resolution for charged particle tracks with |η| < 2 and pT > 0.5 GeV/c. The TRT is immersed in a 2 T magnetic field generated by the central solenoid, significantly contributing together with the other two Inner Detector sub-systems to the particle momentum reconstruction. Along with continuous tracking, it provides particle identification capability through the detection of transition radiation X-ray photons. This talk will describe the operational experience gained with the ATLAS TRT detector during the commissioning with cosmic rays and operation with the first proton-proton collision data at 900 GeV and 7 TeV center-of-mass energy.