GEM-based photon detector for RICH applications

We describe the performance of a novel photon detector based on the Gas Electron Multiplier (GEM). With a CsI photocathode deposited on the first GEM in a cascade, the device permits to efficiently detect and localize single photoelectrons produced by UV photons between the CsI threshold ( ∼ 6.2 eV ) and the quartz window cutoff ( ∼ 7.5 eV ) . The single-photon position accuracy achieved ∼ 55 μ m rms, and the excellent multi-photon resolution makes it well suited for Cherenkov ring imaging applications.