PT Journal AU ATLAS Collaboration (Aaboud, Mea Alvarez Piqueras, D Barranco Navarro, L Cabrera Urban, S Castillo Gimenez, V Cerda Alberich, L Costa, MJ Fernandez Martinez, P Ferrer, A Fiorini, L Fuster, J Garcia, C Garcia Navarro, JE Gonzalez de la Hoz, S Higon-Rodriguez, E Jimenez Pena, J Lacasta, C Mamuzic, J Marti-Garcia, S Melini, D Mitsou, VA Pedraza Lopez, S Rodriguez Rodriguez, D Romero Adam, E Salt, J Sanchez Martinez, V Soldevila, U Sanchez, J Valero, A Valls Ferrer, JA Vos, M TI Performance of the ATLAS Transition Radiation Tracker in Run 1 of the LHC: tracker properties SO Journal of Instrumentation JI J. Instrum. PY 2017 BP P05002 - 42pp VL 12 DI 10.1088/1748-0221/12/05/P05002 LA English DE Particle tracking detectors (Gaseous detectors); Transition radiation detectors AB The tracking performance parameters of the ATLAS Transition Radiation Tracker (TRT) as part of the ATLAS inner detector are described in this paper for different data-taking conditions in proton-proton, proton-lead and lead-lead collisions at the Large Hadron Collider (LHC). The performance is studied using data collected during the first period of LHC operation (Run 1) and is compared with Monte Carlo simulations. The performance of the TRT, operating with two different gas mixtures (xenon-based and argon-based) and its dependence on the TRT occupancy is presented. These studies show that the tracking performance of the TRT is similar for the two gas mixtures and that a significant contribution to the particle momentum resolution is made by the TRT up to high particle densities. ER