The RICH detector of the NA62 experiment at CERN

The RICH detector of the NA62 experiment is one of the key detectors to achieve the muon rejection needed in the search for the ${K^ + } \to {\pi ^ + }\nu \bar \nu $ decay, performed by NA62. Since $BR({K^ + } \to {\mu ^ + }\nu )$ is higher than $BR({K^ + } \to {\pi ^ + }\nu \bar \nu )$ by more than 9 orders of magnitude, it represents one of the most relevant background contributions. Its rejection is performed with kinematic reconstruction of the event and identification of the charged particles in the final state (pions against muons). The Ring Imaging Cherenkov detector (RICH) gives a muon rejection higher than a factor 100 in the momentum range 15-35 GeV/c, and measures the track crossing time with a resolution better than 100 ps. It is also exploited to provide trigger for charged particles. In this contribution the RICH detector will be described, together with its basic performance, the mirrors alignment procedure and its usage in ${K^ + } \to {\pi ^ + }\nu \bar \nu $ search.