A RICH detector for the NA62 very rare kaon decay experiment at CERN

The NA62 experiment is designed to measure the very rare kaon decay K⁺→π⁺νν-bar at the CERN SPS with a statistical precision of less than 10%. The Standard Model prediction for the branching ratio is (8±1)x10^-11. One of the challenging aspects of the experiment is the suppression of the K⁺→μ⁺ν_μ background at the 10^-12 level. To satisfy this requirement we need a Ring Imaging Cherenkov Detector able to separate π^± from μ^± in the momentum range between 15 and 35GeV/c with a muon suppression factor of at least 10^-2. We discuss the design and the construction of a RICH detector with a very long focal length (17m), neon radiator gas at atmospheric pressure and ∼2000 fast photodetectors. With a total time resolution of the order of 100ps this RICH detector can also be used to measure the arrival time of the pion and provide the experiment's trigger