A New Carbon based VUV Mirror of High Radiation Length for the HADES RICH*

S. Winkler, J. Friese, R. Gernhauser, P. Maier-Komor. B. Sailer
Technische Universitat Munchen, Physik Department E12, James Franck Sir. 1, D-85748 Garching, Germany.

April 4, 2002

   The VUV Cherenkov photons radiated by electrons and positrons in the gaseous C4F10 radiator of the HADES RICH are focused by a spherical mirror of 1.5 m diameter and 0.78 m radius of curvature to the padplane of the MWPC photon detector. To match the requirements of maximum radiation length we have produced a mirror based on a novel pure carbon substrate of 2 mm thickness and very high stiffness. The mirror system is segmented into 18 panels mounted on a light weight support structure with a sixfold narrow spoke geometry. The panels are produced from glassy carbon substrates, individually polished and coated with VUV reflective Al-MgF2 layers.
We present the concept of the mirror together with results from offline reflectivity measurements and from in beam experiments with the assembled HADES RICH.

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