Development of RICH detectors and large-area hybrid photodiodes for the LHCb experiment

Abstract

The LHCb experiment is being designed to study CP violation in the B meson sector. It differs from other LHC experiments in its excellent particle identification capability. This is accomplished by two focused RICH counters: RICH 1 has 5 cm thick aerogel and 95 cm long C 4F 10 radiators while RICH 2 uses 180 cm long CF 4 radiator. The combined system will give π/K separation in the momentum range 1–150 GeV/ c. Spherical mirrors are used to focus the Cherenkov light on detection planes equipped with photodetectors. One photodetector option is the large-area Hybrid Photodiode (HPD). An HPD consists of a cylindrical vacuum envelope of 127 mm diameter capped with a spherical borosilicate glass entrance window. Electrodes demagnify the image onto a silicon sensor comprising 2048 pads, each with a surface of 1 mm 2. A large UHV evaporation plant for the production of HPDs with visible light bialkali photocathodes (K 2CsSb) has been built and successfully operated producing photocathodes with good quantum efficiency and stability. A Cold Indium sealing technique has been developed and proven to provide excellent vacuum tightness.