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

Jinhong Shen; Youpeng Wu; Zijian Wang; Leyun Gao; Qite Li; Chen Zhou; Qiang Li; Yu Xu; Xueheng Zhang; Liangwen Chen; He Zhao; Zhiyu Sun; Ruihu Zhu

arXiv · 2607.18669

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

Jinhong Shen·Youpeng Wu·Zijian Wang·Leyun Gao·Qite Li·Chen Zhou·Qiang Li·Yu Xu·Xueheng Zhang·Liangwen Chen·He Zhao·Zhiyu Sun·Ruihu Zhu

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Abstract

We investigate an invisible lepton-flavor-violating scalar $\phi$ with exclusive $e-\mu$ couplings and study its resonant production via $\mu^+e^-\to\phi$ 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 ($6\times10^{10}$ 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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Jinhong Shen, Youpeng Wu, Zijian Wang, Leyun Gao, Qite Li, Chen Zhou, Qiang Li, Yu Xu, Xueheng Zhang, Liangwen Chen, He Zhao, Zhiyu Sun, Ruihu Zhu. 2026-07-21. Production of lepton-flavor-violating scalars through resonant positive-muon annihilation on atomic electrons. https://arxiv.org/abs/2607.18669

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