Performance of the NA62 RICH detector

NA62 is the last generation kaon experiment at CERN SPS aiming to study the decay K+ _ π+νν̅. The goal of the experiment is to measure the decay branching ratio (O(10-10)) with 10% accuracy, collecting about 100 K+ → π+νν̅ events in three years of data taking and assuming a 10% signal acceptance. The NA62 detector must be able to reject background events from decay channels with branching ratios up to 10 orders of magnitude higher than the signal and with similar experimental signature. To this purpose, good Particle Identification (PID) and kinematic rejection are required. Precise timing is also needed to correctly associate the π+ with the parent K+ in a high rate environment. The key element of the PID in NA62 is the Ring Imaging CHerenkov detector (RICH) to identify π and μ in the momentum range between 15 and 35 GeV/c with a muon rejection factor better than 1%; it is also required to measure the pion arrival time with a precision better than 100 ps and the Cherenkov angle with a resolution better than 80 μ rad. Finally, it must provide a fast L0 trigger signal for charged particles. At the beginning of the NA62 pilot run, from mid October to mid December 2014, the RICH detector was completely installed and ready to take data. The installation details and the results on the detector performance will be presented together with preliminary results from the first NA62 physics run in 2015.