Single photon detection with the multi-anode CLAS12 RICH detector

The first module of the hybrid-optics large-area CLAS12 RICH at JLab has been recently put into operation using for the first time the well known Hamamatsu H8500 MAPMT and the new single-photon dedicated H12700, for a total of about 400 MAPMTs and 25000 pixels. The photon detector must efficiently detect single photons in the visible and near-UV light region, provide a fast response for background rejection and pattern recognition, and have a spatial resolution of less than 1 cm over an area of ? 1 m2. Each front-end readout unit is composed of three electronic boards with specific tasks directly connected to groups of 2 or 3 sensors. The core of the readout is composed of MAROC3 and FPGA chips. The MAROC3 chip is able to discriminate the 64 signals from one MAPMT and to produce 64 corresponding binary outputs with 100% efficiency starting at a small fraction of the single-photon signal, while the FPGA chip provides 1 ns TDC capability with 8 ?s maximum latency and acts as a DAQ controller. The system is designed to be almost dead-time free at the foreseen 20 kHz CLAS12 trigger rate. The best working conditions for single-photon detection have been studied at laser stands, test beams, and with the JLab electron beam data. A report of the photon detector preparation, commissioning and operation is here discussed