A TRANSITION RADIATION DETECTOR FOR POSITRON IDENTIFICATION IN A BALLOON-BORNE PARTICLE ASTROPHYSICS EXPERIMENT

We have built and tested a transition radiation detector of about 76 X 80 cm(2) active surface to discriminate positrons from protons in an experiment performed on a balloon flight to search for primordial anti matter. The TRD is made of ten modules each consisting of a carbon fib er radiator followed by a multiwire proportional chamber. In order to achieve a proton-electron rejection factor of the order of 10(-3) with a strict limitation on power consumption to about 40 mW per chamber c hannel, as required by experimental constraints, we have developed a l ow power consumption ''cluster counting'' electronics. Different analy sis procedures of calibration data are shown. In addition, comparisons of the performances of this detector are also made with a previous si milar prototype equipped with standard fast electronics and similar de tectors from other authors.