Beam test performance of a prototype muon trigger detector for the PSI muEDM experiment

We present the design, construction, and beam test results of a prototype muon trigger detector developed for the muon electric dipole moment (muEDM) experiment at the Paul Scherrer Institute (PSI). The muEDM experiment aims to increase the sensitivity of the muon EDM measurement by several orders of magnitude beyond the current limit established by the BNL E821 experiment. Precise and reliable muon identification at the entrance of the storage solenoid is crucial, as the trigger detector must quickly generate a trigger signal to activate a pulsed magnetic kicker, enabling the capture and storage of incoming muons. The trigger detector consists of two primary components: a thin gate detector made from a plastic scintillator read out by eight silicon photomultipliers (SiPMs), and a telescope detector made of four plastic scintillators also read out by SiPMs. The telescope detector operates in anticoincidence with the gate detector, identifying muons that pass through the gate detector without activating the telescope detector, thus ensuring the selection of muons with trajectories optimal for stable storage within the solenoid. A proof-of-principle test was performed at the PSI πE1 beamline using 27.5 MeV/c muons to characterize the detector’s timing performance, scintillator light yield, and triggering efficiency. Experimental data showed excellent agreement with detailed Geant4 Monte Carlo simulations that incorporated optical photon generation, transportation, and detection. The results successfully validate the detector design and confirm its suitability for the stringent timing, efficiency, and trajectory-selection requirements essential to the muEDM experiment.