The Kaon identification system at the NA62 CERN experiment

The main goal of the NA62 experiment at the CERN SPS accelerator is to measure the branching ratio of the ultra-rare K⁺ → π⁺vv decay with 10 % accuracy. This will be achieved by detecting about 100 K⁺ → π+vv decays with a ratio of signal/background ∼ 10 in 2-3 years of data taking. NA62 will use a 750 MHz high-energy unseparated charged hadron beam, with a 6 % kaons component, and a kaon decay-in-flight technique. The kaons must be identified, together with a precise timestamp, in order to guarantee the rejection of background induced by accidental overlap of events in the detector. This is achieved by the kaon identification system, KTAG, which identifies kaons with an efficiency higher than 95 % and 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. The performance of KTAG is presented after setting the detector within the context of the NA62 experiment.