Hadron identification with the HERMES RICH.

B .Hommez

on behalf of the HERMES collaboration

University of Gent,Proeftuinstraat 86, 9000 Gent, Belgium

March 29, 2002

   The HERMES experiment has upgraded its spectrometer in 1998 with a ring imaging Cerenkov (RICH) detector to allow the identification of pions, kaons and protons over practically the entire momentum range of HERMES, by using two radiators, silica aerogel and C4F10 gas. The identification of the different hadrons in the HERMES RICH detector is based on two different methods: the indirect ray tracing method (IRT) and the direct ray tracing method (DRT). Both methods use a likelihood analysis to select the most probable particle type. The IRT and DRT method exist in parallel; a decision network chooses the optimal method for a certain event topology. The efficiencies and contaminations for particle identification have been experimentally determined by the use of decaying Φ, Ks and Λ particles. 
   Details on the IRT and DRT methods will be presented as well as the development of the RICH simulation program which describes the experimental data well.