Single Lepton Identification and Close Pair Recognition in the HADES RICH *

T. Eberl
Technische University at Munchen, Physik Department E12,
James Franck Str. 1, D-85748 Garching, Germany,
for the HADES collaboration

March 29, 2002

     The fast RICH of the new dilepton spectrometer HADES serves as a hadron blind trigger device for e+epairs in hadron and heavy ion induced collisions in the 1-2 A GeV incident energy range. Dalitz decays of abundantly produced π0s and external conversion of high energetic photons in target and radiator (C4F10) are the main sources of e+e- pairs with small opening angles (1-15 degrees). Double rings from such close pairs, if not properly identified and separated, lead to tremendous combinatorial background and screen the physics signal of interest.
    We report on dedicated measurements of fully reconstructed close e+e- pairs from these sources, which allow to extract experimental information on double ring properties as well as on efficiencies for single lepton identification.
The results will be compared to simulation results based on measured optical and electronic properties of the RICH 

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