First Results from the BELLE DIRC Prototype

The DIRC (Detection of Internally Reflected Cerenkov light) is a new type of ring imaging Cerenkov detector, which detects images from Cerenkov light produced in precisely machined quartz bars. The Cerenkov images are transported along several meters of bar to the edge of the detector where they are proximity focussed unto an array of conventional photomultiplier tubes. Results from a prototype device comprising a 2 x 4 x 240 cm**3 quartz bar read by an array of 480 PMT's are presented. Sample images, which are the first observed in this type of detector, are shown. Measurements of the light yield (approximately 20 photoelectrons per image) and the angular resolution are in good agreement with Monte Carlo predictions.