Darmstadt 2008 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 26: Instrumentation und Anwendungen II

HK 26.3: Talk

Tuesday, March 11, 2008, 11:45–12:00, 2D

Calibration of the Alice Transition Radiation Detector — •Raphaelle Bailhache — Gesellschaft fuer Schwerionenforschung, Darmstadt, Deutschland

The Alice Transition Radiation Detector ( TRD), is composed of drift chambers filled with Xe/CO₂ (85/15%). In the nominal conditions of pressure and temperature the drift field of 700 V/ cm corresponds to a drift velocity of the electrons of 1.5 cm/µs resulting in a signal extension of about 2 µs. The nominal gas gain is about 5000 for an anode voltage of 1.55 kV. It is important for the particle identification and the tracking capability of the detector to do an absolute and relative calibration of the drift velocity, the gas gain, the time offset and the width of the pad response function of the 540 chambers of the TRD. Physics events will be used, taking into account the fact that the produced particles are mostly pions and to first order uniformly distributed over the rapidity range |η|<0.9 covered by the detector. To account for the variation of the gas composition, the electric field, the pressure and the temperature, the calibration constants will be obtained every 10 minutes for each of the 18 TRD supermodules, and every run (about 3 hours) per detector. Once per year (10⁹ pp events) every pad ( total number of pads: 1181952) is calibrated against static local non-uniformities of the detector. A first calibration is performed online and can be then improved offline.