Lepton identification with the CsI based RICH of HADES

A Ring Imaging CHerenkov detector is used in the HADES spectrometer to iden tify e(+)e(-) pairs from meson decays produced in hadron and heavy-ion indu ced collisions at a few A GeV incident energy. The full event pattern infor mation of 28 272 pads has to be transferred within 10 mus to an image proce ssor, where the typical lepton rings have to be identified with an efficien cy epsilon > 90%. Together with some information from other detectors, this signature will reduce the amount of data written to tape by a factor of ab out 100. Concept and performance of the RICH and preliminary results of fir st in-beam measurements are presented. (C) 2001 Elsevier Science B.V. All r ights reserved.