System tests of the LHCb RICH photon detectors using charged particle beams

The LHCb RICH detectors use 484 Hybrid Photon Detectors (HPDs), each with an encapsulated 1024 pixel sensor, to detect the Cherenkov light. Three production modules of HPD arrays (one tenth of the total modules), have been tested using Cherenkov radiators in a charged particle beam. Each module contained 12 HPDs, front-end electronics based on FPGA technology and production versions of the low and high (20 kV) voltage distribution boards. Data were readout at the LHC rate of 40 MHz by optical-link transmission at 1.6 GHz. Cherenkov rings have been observed in both N 2 and C 4 F 10 radiators.