Triple-GEM operated in different gases with highly pixelated readout using MediPix2 chip

A triple-GEM setup is successfully operated together with a digital readout chip with a pixel size of 55 × 55 μ m 2 (MediPix2 ASIC). A pad structure surrounding the MediPix2 is used to trigger on 106Ru electrons crossing to the drift volume. The gases used are ArCO 2 and HeCO 2 (70/30). The detected cluster density is about 5.8 cm - 1 . The evaluation of the tracks by a straight line fit to the cluster centers results in small residuals of about 50 – 60 μ m for both gases, if the effect of multiple scattering is taken into account. The “3-point” resolution being much less sensitive to multiple Coulomb scattering is close to 50 μ m . For a modified MediPix2 chip with the drift time information added a TPC readout at the ILC is considered.