The ALICE Transition Radiation Detector TRD

Tariq Mahmoud

Physikalisches Institut, Universitšt Heidelberg, Germany 
for the ALICE TRD collaboration

     ALICE is a dedicated heavy ion experiment at the LHC. One of its central barrel detectors is the Transition Radiation Detector (TRD) with a rapidity coverage of |0.9| < η. It will operate in a very high multiplicity environment. The rapidity density of charged particles in collisions of Pb nuclei at ÷s = 5.5 ATeV is expected to be as high as 8000.
      The TRD consists of 18 sectors in azimuthal direction. Each sector consists of 6 layers in radial and 5 sections in longitudinal direction. That amounts to 540 individual detector modules with a total area of 736 m2 and 1.2 million readout channels. The individual detector elements of each of the 6 layers of the ALICE TRD consist of a radiator, a drift and conversion region filled with Xe/CO2 (85:15), and a multi-wire proportional section with pad readout. The signals induced on the pads are sampled 15 times for the duration of the drift time leading to a total of 17 million readout pixels. The electronics is capable of providing a trigger on high momentum electrons within 6.1 μs.
      In conjunction with the TPC and ITS, the TRD provides sufficient electron identification capability for the following measurements:
The production of light and heavy vector-mesons resonances as well as the dilepton continuum are measured in the di-electron channel. The semi-leptonic decays of hadrons with open charm and open beauty are measured via the single-electron channel and requiring a displaced vertex using the ITS information. Information on the correlated production of hadrons with open charm and open beauty are obtained via coincidences of electrons in the central barrel and muons in the forward muon arm. Jets with high Et can be selected at the trigger level by requiring several high pt tracks in one TRD module.
     The performance for particle identification and tracking has been evaluated in test beams. The design and test beam results will be presented.