High-resolution Micromegas telescope for pion- and muon-tracking

A beam telescope, consisting of four Micromegas detectors with standard copper anodes formed by 360 strips and an active area of 90 mm×100 mm, has been tested in a 160 GeV pion beam at the SPS/CERN. The 1500 anode-strips of 250μm strip pitch are read out using Gassiplex frontend modules. The telescope was operated over several weeks with an efficiency above 98%. Around 6 million pion tracks have been collected, using an Ar:CO2 85:15 gas mixture at 1016 mbar. The study of the single detector spatial resolution yields a best value of 35μm, when maximizing the number of electrons entering the amplification region. The resolution depends only weakly on gas gain and transverse diffusion. The combination of four detectors allows thus for a track accuracy of 20μm. The discharge rate in the pion beam with a flux-density of 4 kHz/cm2 was around 10−5 per pion and thus negligible