RESULTS OF A 1ST BEAM TEST OF HADRON BLIND TRACKERS

We describe the experimental results of a new type of electron tracker , called Hadron Blind Detector or HBD. An HBD prototype was tested wit h gas mixtures of CF4 with He or Ne and a parallel plate avalanche cha mber having a CsI photocathode of eight pads. Beam tests confirm the l arge Cherenkov light bandwidth in the EUV region that can be obtained with such ps mixtures. It results in a large quality factor of about 5 00 cm-1 which allows HBD operation with a much shorter radiator thickn ess than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dal itz pairs, and providing trigger on electrons among heavy hadron backg round. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in hea vy ion colliders.