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 f ollowed by a photosensitive wire chamber using a solid CsI photocathod e. The photon detector lies directly in the particle path and is requi red to have single photo-electron sensitivity and yet be insensitive t o the passage of a charged particle. We have altered the design by add ing 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% ele ctron efficiency: the pion efficiency was 1/333, 1/150, and 1/100 for each of the lengths listed above.