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Construction and characterization of a muon trigger detector for the PSI muEDM experiment

Guan Ming Wong, Tianqi Hu, Samip Basnet, Chavdar Dutsov, Siew Yan Hoh, David Höhl, Xingyun Huang, Timothy David Hume, Alexander Johannes Jäger, Kim Siang Khaw, Meng Lyu, Ljiljana Morvaj, Jun Kai Ng, Angela Papa, Diego Alejandro Sanz Becerra, Philipp Schmidt-Wellenburg, Yusuke Takeuchi, Yonghao Zeng

Abstract

We present the upgraded design, construction, and beam test results for the Muon Trigger Detector (MTD) developed for the muon Electric Dipole Moment (muEDM) experiment at the Paul Scherrer Institute (PSI) in Switzerland. This experiment aims to improve the sensitivity of the muon EDM measurement by more than three orders of magnitude beyond the current limit established by the BNL Muon $g-2$ experiment. Precise identification of storable incoming muons at the entrance of the storage solenoid is essential, as the MTD must rapidly trigger a pulsed magnetic kicker to confine muons in the central region of the solenoid, where a weakly focusing magnetic field is maintained. The MTD comprises two subsystems: a \SI{0.1}{mm}-thick plastic scintillator ``gate detector'' read out by four silicon photomultipliers (SiPMs), and a \SI{5}{mm}-thick CNC-machined plastic scintillator ``active aperture detector'' read out by six SiPMs. The geometry of the active aperture detector was optimized through acceptance studies to maximize both storage efficiency and background veto efficiency. Integrated fast electronics generate an LVTTL trigger signal under an anti-coincidence condition -- a muon detected in the gate but not in the aperture -- ensuring selective triggering of storable muon events for the EDM measurement. The system was tested at the PSI $π$E1 beamline using \SI{22.5}{MeV/\textit{c}} muons under scaled-down conditions to characterize detector response and trigger performance. A Geant4 simulation incorporating detailed optical photon transport and SiPM response modeling was developed and reproduces the measured event topologies with ${\sim}97\%$ agreement. These results validate the detector design and demonstrate the MTD's readiness for deployment in the full muEDM Phase-1 setup.

Construction and characterization of a muon trigger detector for the PSI muEDM experiment

Abstract

We present the upgraded design, construction, and beam test results for the Muon Trigger Detector (MTD) developed for the muon Electric Dipole Moment (muEDM) experiment at the Paul Scherrer Institute (PSI) in Switzerland. This experiment aims to improve the sensitivity of the muon EDM measurement by more than three orders of magnitude beyond the current limit established by the BNL Muon experiment. Precise identification of storable incoming muons at the entrance of the storage solenoid is essential, as the MTD must rapidly trigger a pulsed magnetic kicker to confine muons in the central region of the solenoid, where a weakly focusing magnetic field is maintained. The MTD comprises two subsystems: a \SI{0.1}{mm}-thick plastic scintillator ``gate detector'' read out by four silicon photomultipliers (SiPMs), and a \SI{5}{mm}-thick CNC-machined plastic scintillator ``active aperture detector'' read out by six SiPMs. The geometry of the active aperture detector was optimized through acceptance studies to maximize both storage efficiency and background veto efficiency. Integrated fast electronics generate an LVTTL trigger signal under an anti-coincidence condition -- a muon detected in the gate but not in the aperture -- ensuring selective triggering of storable muon events for the EDM measurement. The system was tested at the PSI E1 beamline using \SI{22.5}{MeV/\textit{c}} muons under scaled-down conditions to characterize detector response and trigger performance. A Geant4 simulation incorporating detailed optical photon transport and SiPM response modeling was developed and reproduces the measured event topologies with agreement. These results validate the detector design and demonstrate the MTD's readiness for deployment in the full muEDM Phase-1 setup.

Paper Structure

This paper contains 15 sections, 1 equation, 19 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Muon Trigger Detector
  3. Design and construction of the muon trigger detector
  4. Detector design with simulations
  5. Detector construction
  6. Readout electronics
  7. Experimental setup of Test Beam 2024
  8. Beam Configurations
  9. Experimental Setup
  10. DAQ
  11. Results and discussion
  12. Detector response and particle identification
  13. Event Topology
  14. Simulation verification
  15. Conclusion

Figures (19)

  • Figure 1: Layout of muEDM Phase-1 experimental setup, showing side-view.
  • Figure 2: Conceptual sketch of the Muon Trigger Detector (MTD).
  • Figure 3: Monte-Carlo generated beam phase space at the exit of the injection tubes. The phase space distributions are based on a measurement at the $\pi$E1 beamline exit, propagated through a tube accounting only for geometric acceptance. Coordinates are given in the laboratory frame with origin at the center of the injection tube exit. Left: $x'$ vs $x$, Right: $y'$ vs $y$.
  • Figure 4: Magnetic fields implemented in simulation, comprising fields of the PSC solenoid, the Correction Coils, and the Weakly Focusing coil. Top: z-component along the solenoid axis; bottom: radial component. The coordinate origin is at the center of the solenoid.
  • Figure 5: Visualisation of virtual storage plane implemented in G4beamline. The orange ellipse highlights the virtual storage plane in a white rectangle.
  • ...and 14 more figures