Study in a beam test of the resolution of a Micromegas TPC with standard readout pads

The results of a beam test performed at the KEK PS in June 2005 are presented. Drift properties of an argon-isobutane mixture have been accurately measured and compared with predictions at magnetic fields between 0 and 1 T. The r.m.s. point resolution of a padrow is compared with simulation and with an analytical calculation. The fundamental limitations due to detector geometry and gas properties are reviewed and the measured performances of the detector are found to be close to this limit. A numerical application to the case of a linear collider Time Projection Chamber (TPC) is presented.