Beam test of FARICH prototype with digital photon counter

In June 2012 we tested a Focusing Aerogel RICH detector prototype based on Digital Photon Counters (DPC) by Philips at the CERN PS T10 beam line with a particle momentum up to 6 GeV/c. The prototype comprises a 20×20 cm2 photon detector with 48×48 DPC pixels. In order to reduce the dark count rate, the photon detector was cooled to −40 °C in addition to disabling individual DPC's microcells. A four layer focusing aerogel radiator with 200 mm focal distance was studied. We obtained a Cherenkov angle resolution of 3.61±0.04 mrad. The mean number of photoelectrons in a ring is 12. Directly measured π/K separation at 6 GeV/c momentum is 3.5σ, μ/π separation is 5.3σ at 1 GeV/c. A comparison with a Monte Carlo simulation is presented as well.