Beam tests of the gas electron multiplier

We describe the results of systematic measurements, carried out with single and double GEM detectors with printed circuit read-out and having an active area of 10×10 cm2, both in the laboratory and in a high-energy charged particles beam at CERN. Using fast analog readout electronics, we demonstrate efficiencies for minimum ionizing particles close to 100%, with typical signal/noise ratios above 50 and up to 103 for the single and double GEM configuration, respectively, and a time resolution of 15 ns fwhm. Localization accuracies around 40 μm r.m.s. have been obtained for perpendicular tracks, degrading to 200 μm at 20° of incidence to the normal. Operated in a non-flammable gas mixture (argon–carbon dioxide), GEM detectors are robust, light and cheap to manufacture, and offer excellent performances and reliability suited for use in the harsh environments met at high luminosity colliders.