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T: Teilchenphysik

T 505: Spurkammern III

T 505.9: Vortrag

Mittwoch, 31. März 2004, 18:15–18:30, HS VI

Performance of Triple GEM Tracking Detectors in the COMPASS Experiment — •Quirin Weitzel¹, Bernhard Ketzer¹, Igor Konorov¹, Stephan Paul¹, Leszek Ropelewski², and Fabio Sauli² — ¹Physik Department, Technische Universität München, D-85748 Garching — ²European Laboratory for Particle Physics CERN, CH-1211 Geneva 23

COMPASS is a high-luminosity fixed target experiment at CERN’s SPS, which has been taking data with a 160 GeV/c muon beam since 2001. The tracking of charged particles in the near-beam area is achieved by a set of twenty novel large-area micropattern gas detectors based on the Gas Electron Multiplier (GEM) [1]. Owing to a two-dimensional readout of signals, each of these detectors delivers two track projections.

While the basic characteristics of these detectors have been studied both in test beams and within COMPASS using a low intensity muon beam [2], this is the first conclusive study of the performance of the full set of detectors during a physics run at nominal muon beam intensity with particle rates up to 10 kHz/mm². All detectors are shown to operate at efficiencies >95%. The spatial resolution is found to be around 70 µm for all detectors. By sampling the analogue signal of each strip at a frequency of 40 MHz the track time can be determined with a time resolution of ∼ 12 ns. Correlations between amplitudes measured on both projections within one detector considerably improve the tracking efficiency and speed by removing ambiguities in multi-hit events.

[1] F. Sauli, Nucl. Instr. Meth. A386, 531 (1997).

[2] B. Ketzer et al., IEEE Trans. Nucl. Sci. 49, 2403 (2002).