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¯ at the CERN SPS with a statistical precision of less than 10%10%. The Standard Model prediction for the branching ratio is (8±1)×10-11(8±1)×10-11. One of the challenging aspects of the experiment is the suppression of the K+→μ+νμK+→μ+νμ background at the 10-1210-12 level. To satisfy this requirement we need a Ring Imaging Cherenkov Detector able to separate π±π± from μ±μ± in the momentum range between 15 and 35GeV/c with a muon suppression factor of at least 10-210-2. 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∼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.