High level performance of the NA62 RICH detector

Abstract

NA62 is the last generation kaon experiment at the CERN SPS aiming to measure the branching ratio of the ultra-rare K+→π+νν̄ decay with 10% accuracy. The challenging aspect of NA62 is the suppression of background decay channels with branching ratios up to 10 orders of magnitude higher than the signal and with similar experimental signature: one of the main backgrounds comes from the K+→μ+νμ decay, therefore a highly powerful pion/muon separation is needed. To this purpose good identification (PID) is required. A key element of PID in NA62 is the Ring-Imaging Cherenkov (RICH) detector. According to the NA62 requirements, the RICH identifies μ+ and π+ in the momentum range between 15 and 35 GeV/c with a muon rejection factor of 10−2. It also measures the arrival time of charged particles with a precision better than 100 ps and is one of the main components of the NA62 trigger system. The RICH detector has been successfully operated during the 2016, 2017 and 2018 data taking periods of NA62, being essential in the analysis leading to the first evidence for the observation of the K+→π+νν̄ decay. NA62 data taking was resumed in 2021. The main design aspects and operational characteristics of the detector are described and a detailed report of its performance concerning the π/μ separation is presented, together with preliminary results about its basic performance in 2021.