Speaker
Description
The lead-aerogel Cherenkov detector used as the beam-hole photon veto (BHPV) has performed well in KOTO, but for high-intensity operation at KOTO II, a detector with better time resolution would be desirable to reduce losses from the interactions of beam particles in accidental coincidence. As an alternative, a compact, high-granularity small-angle calorimeter (SAC) is under study. The SAC design utilizes layers of ultrafast lead tungstate (PWO-UF) crystals offering superior time resolution and radiation tolerance, with high granularity enabling effective neutron/photon discrimination to reduce accidental vetoes. Tests with PWO-UF and PbF₂ crystals have demonstrated promising photoelectron yields and timing performance, and radiation exposure studies have confirmed the durability of PWO-UF. A new prototype with full-size crystals and fast, radiation-hard photomultipliers is now under construction for testing at the CERN PS in late summer. Preliminary results from this beam test will be presented.