Results on the Performance of a Broad Band Focussing Cherenkov Counter

The field of ring imaging (broad band differential) Cherenkov detectors has become a very active area of interest in detector development at several high energy physics laboratories. Our group has previously reported on a method of Cherenkov ring imaging for a counter with large momentum and angular acceptance using standard photo multipliers. Recently, we have applied this technique to the design of a set of Cherenkov counters for use in a particle search experiment at Fermi National Accelerator Laboratory (FNAL). This new detector operates over the range 0.998 < ß < 1.000 in velocity with a ¿ß ~ 2 x 10-4. The acceptance in angle is ± 14 mrad in the horizontal and ± 28 mrad in the vertical. We report here on the performance of this counter.