The kaon identification system in the NA62 experiment at CERN

The main goal of the NA62 experiment at CERN is to measure the branching ratio of the ultra-rare K⁺ → π⁺ vv̅ decay with 10% accuracy. NA62 will use a 750 MHz high-energy un-separated charged hadron beam, with kaons corresponding to ~ 6% of the beam, and a kaon decay-in-flight technique. The positive identification of kaons is performed with a differential Cherenkov detector (CEDAR), filled with Nitrogen gas and placed in the incoming beam. To stand the kaon rate (45 MHz average) and meet the performances required in NA62, the Cherenkov detector has been upgraded (KTAG) with new photon detectors, readout, mechanics and cooling systems. The KTAG provides a fast identification of kaons with an efficiency of at least 95% and precise time information with a resolution below 100 ps. A half-equipped KTAG detector has been commissioned during a technical run at CERN in 2012, while the fully equipped detector, its readout and front-end have been commissioned during a pilot run at CERN in October 2014. The measured time resolution and efficiency are within the required performances.