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 250 μ m 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 35 μ m , 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 20 μ m . The discharge rate in the pion beam with a flux-density of 4 kHz/cm2 was around 10−5 per pion and thus negligible.