THGEM-based photon detectors for the upgrade of COMPASS RICH-1

New Cherenkov photon detectors are being developed for the upgrade of COMPASS RICH-1. The detectors are based on THGEMs, arranged in a three layer architecture, with a CsI film on the first layer acting as a reflective photocathode. The response of THGEMs with various geometries under different conditions has been studied and photon detector prototypes have been built, tested in laboratory and operated during test beam runs providing a typical gain of 105 and a time resolution of better than 10ns. A photon detector prototype with 300×300mm2 active area, operated at the CERN PS T10 test beam in November 2012, has confirmed the validity of this novel technology and has allowed further studies of the detector response.