A simple high efficiency Cherenkov counter

We have developed a threshold Cherenkov counter using a liquid radiator and a simple array of mirrors for light collection. The index of refraction of the fluorochemical radiator is 1.282 (at 400 nm). This is significantly less than that of water (1.33) and thus provides for a higher β threshold. Our device also doubles as a differential Cherenkov counter. It can detect and distinguish particles several centimeters off the optical axis. The counter has been built, tested, and used successfully in several heavy ion experiments [1], [2]. The optical system 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 resolution of pions from kaons and other heavy charged particles at 1 GeV/c with high efficiency. Pulse height spectra were obtained and detection efficiencies were measured for pions of various momenta 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 extremely effective pion veto. It yielded a pion rejection to pion acceptance ratio of 10⁴. The design is one that was easily, quickly, and inexpensively constructed. It enabled the experimenter to build a liquid (differential or threshold) Cherenkov counter with a higher β threshold than that of water and lower than that of Aerogel. There are very few materials that can be used for Cherenkov counter construction with β thresholds in this velocity region