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 fi lm on the fi rst layer acting as a re fl ective 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 10 5 and a time resolution of better than 10 ns. A photon detector prototype with 300 300 mm 2 active area, operated at the CERN PS T10 test beam in November 2012, has con fi rmed the validity of this novel technology and has allowed further studies of the detector response.