A SIMPLE HIGH-EFFICIENCY CHERENKOV COUNTER

We have developed a threshold Cherenkov counter using a liquid radiato r and a simple array of mirrors for light collection. The index of ref raction of the fluorochemical radiator is 1.282 (at 400 nm). This is s ignificantly less than that of water (1.33) and thus provides for a hi gher beta threshold. Our device also doubles as a differential Cherenk ov counter. It can detect and distinguish particles several centimeter s off the optical axis. The counter has been built, tested, and used s uccessfully in several heavy ion experiments [1], [2]. The optical sys tem is designed for maximal pion detection efficiency at a momentum of 1 GeV/c. The counter has a high pion detection efficiency over a wide range of momenta. It produces pulse height distributions that allow r esolution of pions from kaons and other heavy charged particles at 1 G eV/c with high efficiency. Pulse height spectra were obtained and dete ction efficiencies were measured for pions of various moments between 100 MeV/c and 1 GeV/c. These measurements agree well with Monte Carlo simulations. In heavy ion experiments, this counter was used as an ext remely effective pion veto. It yielded a pion rejection to pion accept ance ratio of 10(4). The design is one that was easily, quickly, and i nexpensively constructed. It enabled the experimenter to build a liqui d (differential or threshold) Cherenkov counter with a higher beta thr eshold than that of water and lower than that of Aerogel. There are ve ry few materials that can be used for Cherenkov counter construction w ith beta thresholds in this velocity region.