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 + ν ν ¯ at the CERN SPS with a statistical precision of less than 10 % . The Standard Model prediction for the branching ratio is ( 8 ± 1 ) × 10 - 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 35 GeV / 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 ( 17 m ) , neon radiator gas at atmospheric pressure and ∼ 2000 fast photodetectors. With a total time resolution of the order of 100 ps this RICH detector can also be used to measure the arrival time of the pion and provide the experimentʹs trigger.