The kaon identification system in the NA62 experiment at the CERN SPS

摘要

The fixed target experiment NA62 at CERN aims at measuring the ultra-rare decay K~+→π~+vv, whose branching ratio is of the order of 10~(-11). The main challenges faced by the experiment to achieve a 10% precision measurement are the required beam intensity and background rejection factor. The differential Cherenkov detector KTAG must be able to tag charged kaons in an unseparated hadron beam with an average particle rate of 750 MHz, of which 45 MHz are kaons, with a time precision of at least 100 ps and an efficiency higher than 95%. The additional pion contamination must be kept lower than 10~(-4). The RICH has been designed to separate charged pions from muons in the momentum range 15 < p < 35 GeV/c, contributing to a further muon rejection factor of 100. In order to match the upstream and downstream activity, a time resolution similar to the one of KTAG must be achieved. The RICH is also used as a primitive trigger generator for the level-0 trigger system. The construction and commissioning of both detectors was completed and their performances were studied during the 2014-2015 runs.