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HK: Physik der Hadronen und Kerne

HK 45: Instrumentation and Applications VI

HK 45.6: Vortrag

Donnerstag, 11. März 2004, 18:00–18:15, C

Position Resolution, Electron Identification and Transition Radiation Spectra with Prototypes of the ALICE TRD — •Christian Lippmann — Gesellschaft für Schwerionenforschung, Planckstr. 1, D-64291 Darmstadt, Germany

The ALICE TRD trigger performs online tracking and electron identification and thus requires excellent position resolution and pion rejection. The emission of X-ray transition radiation photons allows to discriminate electrons from pions. A high-Z gas mixture (Xe, CO₂ 15%) is used to provide an efficient photon absorption. The drift chambers are equipped with cathode pads and charge sharing between adjacent pads allows to reconstruct the position of the cluster along a pad row. The drift time is sampled in 20 time intervals of 100 ns (w 1.5 mm) such that two dimensional track reconstruction can be performed.

We tested a stack of four identical small drift chamber prototypes including radiators at the secondary beam facility at the CERN PS. We present the measured momentum dependence of position resolution, angular resolution and electron identification for momenta between 1 and 6 GeV/c, including measurements in a magnetic field. The measured results are well within the design goals. They are compared to (and well reproduced by) simulations based on AliRoot, the ALICE software package. We also discuss the influence of a space charge effect on the results. Moreover, we present our first measurement of the pure transition radiation spectrum produced by our specific radiators. A comparison to simulations at fixed momenta shows good agreement.