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

The NA62 experiment at CERN, aimed to measure the K+ into pion neutrino anti-neutrino branching fraction (O(10^−10)), relies on a Neon based RICH detector for pion/muon separation, time measurement and level 0 trigger. The experimental requirements for this detector are: a muon contamination in pion samples lower than 5×10^−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 (~18 m) Ne filled vessel equipped with a spherical mirror and 414 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 pion/muon separation and to confirm the time resolution obtained with a previous prototype; the μ misidentification probability is about 0.7% and the time resolution is better than 100 ps in the whole momentum range.