Aging measurements of a TMAE-based photon detector for the HERA-B RICH

We report on aging measurements of a photon detector candidate for the HERA-B RICH. The prototype, a proportional wire chamber operated with TMAE, was mounted on an argon filled test-beam RICH and was aged by UV light at rates we expect in HERA-B. We monitored gain and current continuously, and checked the chamber with Cherenkov photons at regular intervals. The number of detected photons/track (projected to 2.75 m C4F10 in HERA-B) dropped from 26 to 11 after two days of aging – well below the 20 required for π/K separation. Based on these results, HERA-B decided to use multi-anode PMTs as photon detectors in the RICH.