Production of lepton-flavor-violating scalars through resonant positive-muon annihilation on atomic electrons

2026/07/21 by Jinhong Shen, Youpeng Wu, Zijian Wang +10
#hep-ph

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Abstract

We investigate an invisible lepton-flavor-violating scalar ϕ with exclusive e-μ couplings and study its resonant production via μ⁺e^-→ϕ in fixed-target experiments. Since the effective center-of-mass energy is determined by the momentum of the initial-state bound electrons, atomic effects can significantly affect the resonance behavior. We therefore employ relativistic bound-state electron wave functions to calculate the production cross section and reveal a material-dependent broadening of the resonance lineshape. For the proposed HIAF experiment, fewer than one day of data taking (6×10¹⁰ MOT) can probe couplings at the 10^-5 level at 90% confidence level near resonance, demonstrating that high-intensity muon fixed-target experiments provide a powerful complementary probe of lepton-flavor violation.

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