The NA62 RICH detector

The RICH detector of the NA62 experiment at CERN SPS is required to suppress $\mu^+$ contamination in $K^+ \to \pi^+ \nu \bar\nu$ candidate events by a factor at least 100 between 15 and 35 GeV/c momentum, to measure the pion arrival time with $\sim 100$ ps resolution and to produce a trigger for a charged track. It consists of a 17 m long tank filled with Neon gas at atmospheric pressure. \v{C}erenkov light is reflected by a mosaic of 20 spherical mirrors placed at the downstream end of the vessel and is collected by 1952 photomultipliers placed at the upstream end. The construction of the detector will be described and the performance reached during first runs will be discussed.