Pion-muon separation with a RICH prototype for the NA62 experiment

The NA62 experiment at CERN, aimed to measure K(+) -> pi + v (v) over bar branching fraction (O(10(-10))), relies on a Neon based RICH detector for pi/mu separation, time measurement and level 0 trigger. The experimental requirements for this detector are: a muon contamination in pion samples lower than 5 x 10(-3) in the momentum range 15-35 GeV/c and a time resolution on the charged track better than 100 ps. A prototype of such a detector was built and tested in 2009: it consists of a full length (approximate to 18 m) Ne filled vessel equipped with a spherical mirror and pi/mu PMs on its focal plane, located about 17 m upstream of the mirror. This prototype was tested at CERN SPS on a positive hadron beam, in the required momentum range, to measure the nip separation and to confirm the time resolution obtained with a previous prototype; the p misidentification probability is about 0.7% and the time resolution is better than 100 ps in the whole momentum range.