Development of a Cerenkov Trigger Detector for the COMET Experiment

Theoretical models beyond the Standard Models predict that a branching ratio of the muon-toelectron (µe) conversion increases to about 10 -15 , although the Standard Model contribution restricts it to be less than 10 -54 .The COMET experiment searches for the µe conversion with signal event sensitivity of 10 -15 in the first phase (Phase-I).A cylindrical detector consisting of a cylindrical drift chamber and a trigger detector will be used for detecting signal electrons.We designed the CDC trigger detector for the COMET Phase-I, and constructed a 1st prototype.Using cosmic rays, we studied the performance of the prototype.A signal to noise ratio (S/N) of 16.9 ± 0.5 was measured.To improve S/N, we started construction of a 2nd prototype.