Thin gap chambers in ATLAS

Thin gap chambers with anode and cathode readouts have been developed for use in the muon trigger system of the end-cap muon spectrometer in the ATLAS experiment. As a first-level trigger, they have to provide high efficiency and excellent time resolution for bunch-crossing tagging in a high-background environment (up to 103 particles/s/cm2). We report here on the construction and the testing of the first prototype for ATLAS; the efficiency was found to be more than 99%, and the fraction of anode signals arriving inside a time window of 25 ns was found to be better than 99%. The test also showed a high-rate capability up to 20 kHz/cm2.