A study of the angular resolution of the ALICE HMPID CsI-RICH detector

In this report is presented an investigation of the Cherenkov angleresolution $\sigma_{\theta_c}$ achievable in the High MomentumParticle Identification (HMPID) CsI-RICH detector of ALICE.Two angle reconstruction procedures are described and the single contributions affecting the resolution are evaluated throughthe analytical treatment and the Monte Carlo simulation program{\em RICHSIM}. The $\sigma_{\theta_c}$ dependence on various detector parameters, namely the radiator thickness, the proximity gap thickness and the chamber gain, has been studied carrying out beam tests of CsI-RICH prototypes.A ring resolution of about 2 mrad has been achieved,for $\beta$=1 particles, in the optimal detector configuration (10 mm C$_6$F$_{14}$ radiator thickness, 103 mm proximity gap and 40 ADC channels single electron averagepulse height).