Positron Transport System for Muonium-to-Antimuonium Conversion Experiment

Muonium-to-Antimuonium Conversion Experiment (MACE) aims to find the charged lepton flavor violation (cLFV) process. A key component of MACE is the positron transport system (PTS) to collect and transport atomic positrons from antimuonium decays, which consists of an electrostatic accelerator and a solenoid beamline. Through field simulations in $\text{textsc}COMSOL$ and particle transport simulations based on $\text{textsc}Geant4$, the PTS can achieve a geometric acceptance of the signal at 65.81(4)% along with a position resolution of 88(1)~$\mu$m~$\times$~102(1)~$\mu$m. The system achieves 322.4(1)~ns transit time with a spread of 6.9(1)~ns, which allows for a TOF-based rejection of internal conversion backgrounds by a factor of ${10}^{-7}$. These promising results pave the way for new-physics signal identifications and background rejections in MACE and offer a novel paradigm for internal transport system in high-intensity frontiers.