We present the performances of large area CsI-RICH prototypes obtained in s
ingle-particle events. The differential quantum efficiency of the photocath
odes has been deduced from Cherenkov rings by means of two different proced
ures: a direct measurement with a thin NaF radiator and a Monte Carlo-based
estimation for a C6F14 radiator. A factor of merit of 45 cm(-1) has been f
ound for the typical detector configuration. Two angle reconstruction algor
ithms have been used and the different errors affecting the Cherenkov angle
resolution have been estimated combining the analytical treatment and the
Monte Carlo simulation. Also the dependence on radiator thickness, Cherenko
v ring radius, chamber voltage and particle incidence angle has been studie
d. (C) 1999 Elsevier Science B.V. All rights reserved.