Particle Identification with the LHCb RICH System

The LHCb experiment uses a Ring Imaging Cherenkov (RICH) system to provide particle identification over the momentum range 2-100 GeV/c. Two RICH detectors are employed. The upstream detector, RICH1, utilizes both aerogel and C$_4$F$_{10}$ gas radiators whilst the downstream RICH2 uses a CF$_4$ gas radiator. The RICH2 detector has been fabricated and is installed in the LHCb interaction region; RICH1 has a programme of phased design and construction. Novel Hybrid Photon Detectors (HPDs) have been developed in collaboration with industry to detect the Cherenkov photons in the wavelength range 200-600 nm. The HPDs are enclosed in iron shielding and Mumetal cylinders to allow operation in magnetic fields up to 50mT. The performance of pre-series HPDs and the results obtained from a particle test beam using the full LHCb readout chain is presented. The production of a total of 484 HPDs required for the two RICH detectors has recently commenced. The expected performance of the LHCb RICH system, obtained from realistic simulation, is described.