The hybrid MPGD-based photon detectors of COMPASS RICH-1

Novel gaseous detectors of single photons for RICH applications have been developed and installed on COMPASS RICH-1 in 2016, covering a total area of 1.4 m2. They have a hybrid architecture consisting of two staggered THGEM layers (one equipped with a CsI photoconverting layer) and a bulk Micromegas and operate stably and efficiently, providing a single photon angular resolution of ∼1.8 mrad and about 10 detected photons per ring at saturation. The main aspects of their construction, commissioning, characterization and performance are presented.