A hydrogen-filled Cherenkov detector for Kaon tagging at the NA62 experiment at CERN

The NA62 experiment at CERN uses a Cherenkov differential counter with achromatic ring focus (CEDAR) with a bespoke readout system to identify charged kaons in an unseparated hadron beam. A new hydrogen-filled CEDAR (CEDAR-H) was constructed to reduce the amount of material in the path of the beam, including an optical system accounting for the dispersive properties of hydrogen. The new detector was designed using detailed simulation, with its performance validated during a test beam at CERN. The CEDAR-H was installed and commissioned at the NA62 experiment in early 2023. The detector improves on the previously used nitrogen-filled CEDAR and exceeds the requirements of both the efficiency of kaon identification and the resolution on determining the kaon crossing time.