A GEM-based TPC prototype for PANDA

A GEM-Based TPC is a very promising option for the central tracker of the PANDA experiment. PANDA is a spectrometer which will detect charged and neutral particles emitted over the full solid angle from 2 × 10⁷ pp annihilations per second to perform high-precision studies in the field of non-perturbative QCD. The central tracker of the spectrometer has to provide good momentum resolutions and at the same time have a very small material budget in order to minimize secondary interactions or photon conversion. A TPC ideally fulfills these requirements, and, in addition, provides particle identification by measuring the specific energy loss. The GEM technology, used for gas amplification, provides an intrinsic suppression of ion backflow usually done by an ion gate for a wire chamber, inappropriate here because of the continuous nature of the beam. A small GEM-TPC prototype was built and characterized with cosmic muons. An average resolution of 200 ¿m had been achieved using the PASA/ALTRO readout electronics. In order to perform more detailed investigations of the detector performance in various conditions, a tracking telescope was set up at the electron beam at ELSA, Bonn, Germany. The characterization of the external tracking telescope has begun in December 2008 and the first electron tracks was observed in the TPC.