ATLAS Transition Radiation Tracker (TRT): Straw Tube Gaseous Detectors at High Rates

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three tracking subsystems of the ATLAS Inner Detector. The ATLAS detector is located at LHC/CERN. We report on how these gaseous detectors (“straw tubes”) are performing during the ATLAS 2011 and 2012 runs where the TRT experiences higher rates than previously encountered. The TRT contains ~300000 thin-walled proportional-mode drift tubes providing on average 30 two-dimensional space points with ~130 µm resolution for charged particle tracks with |η| < 2 and pT > 0.5 GeV. Along with continuous tracking, the TRT provides electron identification capability through the detection of transition radiation X-ray photons. During the ATLAS 2012 proton-proton data runs, the TRT is operating successfully while being subjected to the highest rates of incident particles ever experienced by a large scale gaseous tracking system. In the second half of 2012, the TRT has collected data in an environment with instantaneous proton-proton luminosity of ~0.8 × 10³⁴ cm⁻² s⁻¹. While shadowing effects caused by up to 40 simultaneous proton-proton collisions per bunch crossing are noticeable, the TRT performs significantly better than design. It also contributes to the combined tracking system pT resolution and to electron identification. During LHC heavy ion running in 2011, the TRT contributed to measuring track pT even in events where overall occupancy exceeded 50%.