The ATLAS detector

Transition Radiation Tracker (TRT)

The Transition Radition Tracker (TRT) is one part comprising the inner detector of ATLAS, a general purpose detector for the LHC in CERN. The TRT aids in the tracking of a variety of charged particles produced in both proton-proton and heavy ion collisions. The tracks of various particles helps to constrain the momentum of all long-lived charged particles. Furthermore the TRT will provide particle identification for electrons. The Lund ATLAS group is involved in the calibration, maintenance, development and efficacy of the Transition Radiation Tracker (TRT).
ATLAS Inner Detector
TRT Basics Lund Involvement

The TRT is a so called straw detector. It consists of almost half a million straws with a diameter of 4 mm. Each straw is a small cylindrical proportional chamber, with an anode wire in the centre in 1.78 keV potential, and the straw wall acting as a cathode.

Charged particles passing through the straw ionize the gas in the straw (The gas is comprised of 70% Xe + 20% CF4 + 10% CO2). The ionization cluster is amplified when drifting in the electric field. The amplification factor is about 2.5×104, and the maximum drift time is 45 ns. The intrinsic resolution, obtained by measuring the drift-time of the ionization cluster, is about 130 micrometres.

The space between the straws is filled with material, in order that relativistic particles travelling through the material results in transition radiation. This is radiation created at the boundary between two materials leading to photon emissions. Transition radiation consists of photons, which are strongly forward peaked (angle is relative to 1/g, where g=E/m).

The Xenon in the straw gas reacts with photons and a signal is produced which has a higher amplitude than the normal signal originating from particles passing by. Electrons start producing transition radiation when their momentum is close to 1 GeV, while pions start to radiate only when their momentum is close to 100 GeV - thus, the TRT is able to distinguish an electron from a pion.

  • In Lund we are involved and responsible for the calibration of the TRT whilst experiments are taking place. The calibration involves constantly adjusting and tuning the values of constants used in modelling the electronic response and tracking of the TRT. This ensures that the efficiency of particle identification and tracking within the TRT is maximised, thereby improving the resolution and track parameters of the event reconstruction and correspondingly our physics analysis. For more details see here.

  • We are also involved in the Data Quality of the readouts produced from the detector. Monitoring the quality of the data produced from events recorded in the detector allows a handle on the meaningfulness of the results. The data quality work is maintained both offline(at Lund) and online(at CERN).

  • Previously, Lund had been involved in designing and building the TRT front-end electronics, for more details see here (not up-to-date). We designed and manufactured various printed circuit boards (roof-boards, tension plates), which are needed for the detector data read-out. Furthermore, Lund had helped in the construction and testing of various prototypes of the detector.

Members involved in TRT

  • Torsten Akesson
  • Alejandro Alonso (Calibration Expert)
  • Simona Bochetta (Calibration Expert)
  • Anthony Hawkins
  • Else Lytken
  • Bernhard Meirose
  • Oxana Smirnova
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