Tracking properties of the ATLAS Transition Radiation Tracker (TRT)

The tracking performance parameters of the ATLAS Transition Radiation Tracker (TRT) as part of the ATLAS Inner Detector (ID) are described for different data taking conditions in proton-proton collisions at the Large Hadron Collider (LHC). These studies are performed using data collected during the first (Run 1) and the second (Run 2) periods of LHC operation and are compared with Monte Carlo simulations. The performance of the TRT, operating with Xe-based (Xe-based) and Argon-based (Ar-based) gas mixtures and its dependence on the TRT occupancy is presented. No significant degradation of position measurement accuracy was found up to occupancies of about 20\% in Run 1. The relative number of reconstructed tracks in ID that also have a extension in the TRT was observed to be almost constant with the increase of occupancies up to 50\%. Even in configurations where tracks are close to each other, the reconstruction algorithm is still able to find the correct TRT hits and properly reconstruct the tracks.