Successful test of a prototype hadron blind detector

We have constructed and tested a threshold Cherenkov detector inspired by the conceptual design of Giomataris and Charpak (Nucl. Instr, and Meth. A 310 (1991) 589). The basic design consists of a gas radiator followed by a photosensitive wire chamber using a solid CsI photocathode. The photon detector lies directly in the particle path and is required to have single photo-electron sensitivity and yet be insensitive to the passage of a charged particle. We have altered the design by adding a thin LiF window. This window allows one to separate the radiator and avalanche volumes, giving greater flexibility in the gas choices. Our detector was operated with C2F6 as the radiator gas at lengths of 120, 80, and 40 cm. The avalanche gas was 95% He + 5% CH4. At 95% electron efficiency: the pion efficiency was 1/333, 1/150, and 1/100 for each of the lengths listed above.