Development of a Cylindrical Trigger Hodoscope for the COMET Experiment

Charged lepton flavour violation (CLFV) provides an experimental probe into new physics beyond the Standard Model. The COMET experiment at the Japan Proton Accelerator Research Complex (J-PARC) in Tōkai, Japan will be using the highest intensity muon beam yet to search for muon to electron conversion, a CLFV process, with the best sensitivity so far. Taking a staged approach to this search, Phase-I of COMET will begin in 2024 with a planned single event sensitivity of $3\times 10^{-15}$. In order to reach this sensitivity, a cylindrical trigger hodoscope detector (called the CTH detector) is being developed in order to trigger on high momentum electrons coming from conversion events and provide timing information with better than 1 ns precision. The CTH detector will be capable of operating in a high hit rate, high radiation environment. In preparation for the construction of the CTH detector, 100 MeV electron beam tests were performed at the Australian Synchrotron to characterise prototype CTH detector counters. The target timing resolution was achieved as well as no strong positional dependence in light yield observed along the counter, meeting the requirements for Phase-I in these characteristics.