New developments for the GEM-based TPC for PANDA

The PANDA experiment is an internal target experiment at the High Energy Storage Ring (HESR) at the new Facility for Antiproton and Ion Research (FAIR) at Darmstadt. A TPC is proposed as the central tracker due to its good position and momentum resolution, its low material budget, and its particle identification capabilities via ionization measurements. The continuous nature of the antiproton beam makes the use of a traditional ion gate impractical and hence GEM foils are used for gas amplification, due to their intrinsic ion back flow suppression properties. A small prototype of this GEM-TPC (diameter 200mm, drift length 77mm) has been built and characterized with cosmic muons using a rectangular pad readout structure. The chamber has recently been upgraded with a new readout plane with hexagonal pads, and new front end electronics, based on the AFTER ASIC. The performance of the detector is expected to improve significantly and is currently being studied at a beam test at the ELSA accelerator at Bonn. Preliminary results are presented in this talk.