The ring imaging Cherenkov detectors of the LHCb experiment

Particle identification is one of the key requirements of the LHCb experiment. The ability to distinguish between pions, kaons and protons in a variety of final states is essential for the study of CP violation and rare decays of B hadrons. The particle identification system is composed of two RICH detectors, covering the full angular acceptance of the spectrometer and designed to give particle identification for the momentum range of 1 up to 100 GeV/c. The two RICH detectors are based on gaseous (C4F10 and CF4) and aerogel radiators and an optical system of spherical and flat mirrors which focuses the Cherenkov photons onto the photon detectors planes. These are equipped with a total of 484 Hybrid Photon Detectors (HPDs). The silicon pixel detector of each HPD is read out to give a resolution on the photocathode of 2.5 × 2.5 mm 2 . First experience and results from RICH commissioning and operation at the LHC will be discussed.