Test beam results from the CLEO III LiF-TEA RICH

The CLEO collaboration is preparing a major upgrade of its present detector including a RICH detector for particle identification. This subdetector sy stem follows the 'proximity focussing' design and uses Lithium Fluoride (Li F) crystal radiators and MWPCs filled with a CH4/TEA gas mixture. Part of t he radiator crystals will have the new 'sawtooth' geometry. We have tested the first two of the 30 detector modules together with the first radiator c rystals in a muon halo beam at Fermilab. For the measurement of the Cherenk ov angle we obtain a single photon measurement error of 13.5 mrad for the c onventional planar radiator. With 14 detected photons we find a resolution per track of 4.5 mrad. In the first measurement ever of a 'sawtooth' radiat or we achieve a resolution of 11.8 mrad for single photons and 4.8 mrad per track for 12.3 detected photons with a reduced geometric acceptance. These results fulfill CLEO III requirements. (C) 1998 Elsevier Science B.V. All rights reserved.