Design of a large area fast RICH detector with CsI photocathode for particle identification at ALICE-LHC

ALICE, A Large Ion Collider Experiment, at the LHC collider operated with heavy-ion beams, envisages a Ring Imaging Cherenkov detector (RICH) system to identify particles in the momentum range: .7 GeV/c ÷ 2.5 GeV/c, as an alternative to a time of flight (TOF). In 1992 an extensive R&D programm was started to design and optimize a fast RICH detector based on proximity focusing of the Cherenkov radiation on a wire chamber with a Cesium Iodide solid photocathode. The implementation of an analog pad read-out scheme provides two dimensional information and efficient discrimination between ionizing particle and Cherenkov photoelectron impact points. After a discussion on the requirements, a description of the first large area prototype follows. Results of a beam test and detector performances are finally reported together with future developments and engineering issues.