Construction and performance of a micro-pattern stereo detector with two gas electron multipliers

The construction of a micro-pattern gas detector of dimensions 40 x 10 cm(2) is described. Two gas electron multiplier foils (GEM) provide the internal amplification stages. A two-layer readout structure was used, manufactured using the same technology as the GEM foils. The strips of each layer cross at an effective crossing angle of 6.7degrees and have a 406 mum pitch. The performance of the detector has been evaluated in a muon beam at CERN using a silicon telescope as reference system. The position resolutions of two orthogonal coordinates are measured to be 50 mum and 1 mm, respectively. The muon detection efficiency for two-dimensional space points reaches 96%. (C) 2001 Elsevier Science B.V. All rights reserved.