Monte Carlo study of a Belle II proximity focusing RICH with aerogel as a radiator

A proximity focusing RICH will be installed in the forward direction of the Belle II spectrometer, inside a super conducting solenoid coil with the magnetic field of 1.5 T. Photons emitted in the sequence of two different aerogel radiator layers will be registered by the Hybrid Avalanche Photo Diodes. By detecting more than 11 photons per incident 4 GeV/c pion, with 15 mrad single photon Cherenkov angle resolution, the designed detector should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5 GeV/c up to 4 GeV/c. The particle separation will be based on a two-dimensional extended maximum-likelihood analysis. The position dependence of the efficiencies for identification of pions and kaons shows a very homogeneous response over the detector area. The performance on the edge of the detector is improved by employing planar mirrors to reflect the Cherenkov photons on the detector plane. The results show that by using a designed detector configuration the kaon pion separation efficiency of more than 95% can be achieved at a very low pion misidentification probability of 1%. In the low momentum region (0.5 GeV/c-0.8 GeV/c) the variation of detected number of photons due to matching of aerogel refractive index and the gaps between the sensitive areas on the detector plane results in a slightly decreased separation efficiency.