Same-sign dimuon probe of charged lepton flavor violation at electron-photon colliders

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Hauptverfasser: Zhang, Zhong, Zhang, Yu, Wang, Zeren Simon
Format: Preprint
Veröffentlicht: 2026
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author Zhang, Zhong
Zhang, Yu
Wang, Zeren Simon
author_facet Zhang, Zhong
Zhang, Yu
Wang, Zeren Simon
contents Observation of charged lepton flavor violation would constitute unambiguous evidence for physics beyond the Standard Model (SM). We identify a previously unexplored same-sign dimuon signature in electron-photon collisions, $γe^- \to e^+μ^-μ^-$, mediated by an axionlike particle (ALP) with flavor-violating $e$-$μ$ couplings. The absence of irreducible SM backgrounds and the on-shell production of the ALP render this channel intrinsically clean and highly sensitive, with only small residual backgrounds arising from detector effects. Such collisions can be realized via laser Compton backscattering at $e^+e^-$ colliders including BEPC-II with the BESIII detector, STCF, and ILC. We find that STCF and ILC can probe couplings one to two orders of magnitude below existing bounds. This combination of resonant production, vanishing irreducible background, and same-sign topology would be difficult to achieve in conventional $e^+e^-$ or hadron-collider environments, establishing electron-photon collisions as a uniquely powerful probe of charged lepton flavor violation.
format Preprint
id arxiv_https___arxiv_org_abs_2603_26044
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Same-sign dimuon probe of charged lepton flavor violation at electron-photon colliders
Zhang, Zhong
Zhang, Yu
Wang, Zeren Simon
High Energy Physics - Phenomenology
High Energy Physics - Experiment
Observation of charged lepton flavor violation would constitute unambiguous evidence for physics beyond the Standard Model (SM). We identify a previously unexplored same-sign dimuon signature in electron-photon collisions, $γe^- \to e^+μ^-μ^-$, mediated by an axionlike particle (ALP) with flavor-violating $e$-$μ$ couplings. The absence of irreducible SM backgrounds and the on-shell production of the ALP render this channel intrinsically clean and highly sensitive, with only small residual backgrounds arising from detector effects. Such collisions can be realized via laser Compton backscattering at $e^+e^-$ colliders including BEPC-II with the BESIII detector, STCF, and ILC. We find that STCF and ILC can probe couplings one to two orders of magnitude below existing bounds. This combination of resonant production, vanishing irreducible background, and same-sign topology would be difficult to achieve in conventional $e^+e^-$ or hadron-collider environments, establishing electron-photon collisions as a uniquely powerful probe of charged lepton flavor violation.
title Same-sign dimuon probe of charged lepton flavor violation at electron-photon colliders
topic High Energy Physics - Phenomenology
High Energy Physics - Experiment
url https://arxiv.org/abs/2603.26044