The fast CsI based RICH of HADES*

R. Gernhäuser

Technische Universität München, Physik Department E12,
James Franck Str. 1, D-85748 Garching, Germany,
for the HADES collaboration

March 8, 2002

     A very compact, fast Ring Imaging CHerenkov detector (RICH) in combination with a Time of Flight and Preshower wall is used for lepton - hadron discrimination in the new dilepton spectrometer HADES at GSI, Darmstadt. The detector system is used to identify e+e- pairs from meson decays produced in hadron and heavy-ion induced collisions at a few AGeV incident energy. The Cherenkov detector is essentially hadron blind to cope with the high multiplicity hadronic background of central heavy ion reactions. The RICH is equipped with a gaseous C4F10 radiator and a MWPC type photon detector operated with CH4 at normal pressure. The 28272 readout pads are coated with a solid CsI photon converter and allow an efficient and position sensitive read out of single photo electrons.
     The RICH has been successfully and reliably operated in several runs with altogether ~ 108 C+C collisions. The combined analysis of RICH and TOF signals allows for a very efficient electron-pion separation in the momentum region of interest, from 100 MeV/c to 2500 MeV/c-.
     The setup of the RICH with its particular components will be presented together with measurement results for relevant parameters and experimentally deduced lepton identification efficiencies.

* supported by BMBF (6TM970I) and GSI (TM-FR1).