Photon Detection Efficiency in the CsI based HADES RICH*

L. Fabbietti

Technische Universitat Munchen, Physik Department E12,
James Franck Sir. 1, D-85748 Garching, Germany,
for the HADES collaboration

April 3, 2002

   A gaseous RICH with CsI photo cathode is used for lepton identification in the dilepton spectrometer HADES. A Monte-Carlo based understanding of the detection and recognition efficiency of VUV photons and the Cherenkov ring patterns detected on the MWPC padplane is a prerequisite for the quantitative determination of lepton identification efficiencies.
   We have performed a dedicated in beam measurement to study the response of the RICH detector to the photon signal using the well defined amount of Cherenkov light radiated from carbon ions passing a solid radiator. Spectral efficiencies for single VUV photon detection in the wavelength region from 140 - 220 nm were measured and an experimental figure of merit (No) for the whole RICH could be deduced. The results of these studies were used to optimize the simulation package for the RICH and to determine lepton identification efficiencies in full scale GEANT calculations.

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