KTAG: The Kaon Identification Detector for CERN experiment NA62

In the study of ultra-rare kaon decays, CERN experiment NA62 exploits an unseparated monochromatic (75 GeV/ c ) beam of charged particles of flux 800 MHz, of which 50 MHz are K+ . Kaons are identified with more than 95% efficiency, a time resolution of better than 100 ps, and misidentification of less than 10 −4 using KTAG, a differential, ring-focussed, Cherenkov detector. KTAG utilises 8 sets of 48 Hamamatsu PMTs, of which 32 are of type 9880 and 16 of type 7400, with signals fed directly to the differential inputs of NINO front-end boards and then to TDC cards within the TEL62 system. Leading and trailing edges of the PMT signal are digitised, enabling slewing corrections to be made, and a mean hit rate of 5 MHz per PMT is supported. The electronics is housed within a cooled and insulated Faraday cage with environmental monitoring capabilities.