Calibration of the ATLAS Transition Radiation Tracker

The Transition Radiation Tracker (TRT) is the outermost charged particle tracking device of the ATLAS Inner Detector. The TRT has about 300,000 straws, each of which is a proportional drift tube with a diameter of 4 mm. For a precise measurement of the trajectory of a charged particle (track), the relation between the measured time of the start of the signal and the distance of closest approach between the track and the anode wire needs to be calibrated. In this note, we present the calibration of the TRT detector during the first year of 7 TeV collision data-taking.