Hadron identification with the HERMES RICH

The HERMES experiment has upgraded its spectrometer in 1998 with a ring imaging Cherenkov (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 inverse 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. Details on the IRT and DRT methods will be presented as well as the development of an “unfolding program” which allows to extract true (π,K,p) momentum distributions from the measured ones.