The Kaon identification system of the NA62 experiment

The main goal of the NA62 experiment at the CERN SPS is to measure the branching ratio of the ultra-rare K⁺→π⁺v v decay with 10% accuracy. This can be achieved by detecting about 100 Standard Model events with 10% background in 2 - 3 years of data taking. NA62 is exposed to a 750MHz high-energy unseparated charged hadron beam, with a 6% kaons component, and uses kaon decay-in-ight technique. Precise timing matching of the incident kaon and of the downstream charged track is essential to reject accidental coincidences when working in such a high rate environment. This is achieved by the kaon tagging system KTAG, which identifies kaons with an eficiency higher than 95% and provides precise time information with a resolution better than 100 ps. KTAG re-uses the Cherenkov radiator and optics of a CEDAR, a ring-focusing Cherenkov detector designed for MHz beam intensity in the 1970s. To reach the required performance, KTAG is equipped with new photon detectors, electronics readout, mechanics, cooling and safety systems.