Micropattern gaseous detectors in the COMPASS tracker

The tracking of particles in the region close to the high-intensity beam of the COMPASS experiment at CERN is based on two novel types of micropattern gaseous detectors, the Micromegas and the GEM. Chosen for their high localization accuracy and rate capability, intrinsic to this technology of highly granular gaseous devices, their large active area of up to 40×40 cm2 and small material budget offer additional advantages for tracking of particles in a high-luminosity experiment. The basic principles of these detectors as well as the design adopted for the COMPASS experiment, aiming at optimization of operation according to their positions in the spectrometer, are presented. Means to minimize the probability of gas discharges, and to reduce their impact on detector operation, as implemented for both detector types, are discussed. For the 2001 run of COMPASS, over 50% of the total number of detectors required for the full setup was installed and successfully operated. First results concerning the operational characteristics in the COMPASS muon beam are presented.