SPATIAL RESOLUTION STUDIES OF MICRO PATTERN GAS DETECTORS USING THE CHARGE DISPERSION SIGNAL

The Time Projection Chamber (TPC) for the International Linear Collider will need to measure about 200 track points with a spatial resolution close to 100 mu m. A Micro Pattern Gas Detector (MPGD) readout TPC could achieve the desired resolution with existing techniques using sub-millimeter pad width at the expense of a large increase in the detector cost and complexity. A new MPGD readout concept of charge dispersion developed in Canada has been recently applied to small prototypes MPGD-TPC. Using cosmic-ray tracks, it demonstrated the feasibility of achieving good resolution with pads similar in width to the ones used for the proportional wire TPC. The charge dispersion technique was used with GEM and micromegas and results on resolution studies are presented. The TPC resolution with GEM and micromegas readout are compared to the earlier results without charge dispersion. First results of performance with charge dispersion in a magnetic field of strength comparable to that for the ILC detector are presented. An unprecedented 50 pm resolution has been achieved, which is an important step toward demonstrating the feasibility of meeting the challenging ILC TPC goal.