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Searching for lepton flavor violating decays of the Higgs boson into $μ τ$ , $e τ$ , and $e μ$ final states at FCC-ee

Pongsakorn Sriling , Rutjanaret Uttho , and Vichayanun Wachirapusitanand

Norraphat Srimanobhas ^*

Patipan Uttayarat

Center of Excellence in High Energy Physics, Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

Center of Excellence in High Energy Physics, Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand and CERN, European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland

Theoretical High-Energy Physics and Astrophysics Research Unit, Department of Physics, Srinakharinwirot University, 114 Sukhumvit 23 Road, Wattana, Bangkok 10110, Thailand

^*Contact author: Norraphat.S@chula.ac.th

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Phys. Rev. D 114, 075026 – Published 20 October, 2026

DOI: https://doi.org/10.1103/hs3z-6tnr

Abstract

We investigate the projected sensitivity of the Future Circular Collider in $e^{+} e^{-}$ mode (FCC-ee) in probing the lepton flavor violating (LFV) decay of the 125 GeV Higgs boson, $h \to μ τ$ , $h \to e τ$ , and $h \to e μ$ at center-of-mass energy of 240 GeV with an integrated luminosity of $5 {ab}^{- 1}$ . With the clean multilepton final states, we consider the Higgs production modes that contribute to $e^{+} e^{-} \to ℓ ℓ h$ , in particular, the Higgs-strahlung and the vector boson fusion production channels. The 95% confidence level upper limits on branching ratio are found to be $5.94 \times 10^{- 4}$ , $6.28 \times 10^{- 4}$ , and $7.37 \times 10^{- 5}$ for the channels $h \to μ τ$ , $h \to e τ$ , and $h \to e μ$ , respectively. In addition, we also consider the LFV decay of a new $CP$ -even Higgs boson with mass in the range of 110–200 GeV. The projected FCC-ee sensitivities are then compared to those from low-energy searches for $ℓ \to ℓ^{'} γ$ decay. We find that the FCC-ee sensitivity for the LFV decays of the Higgs boson in the $e - τ$ and $μ - τ$ channels is superior to the low-energy constraints. However, in the $e - μ$ case, the low-energy search offers stronger constraints.

Physics Subject Headings (PhySH)

Extensions of Higgs sector

Article Text

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Phys. Rev. D 114, 075026– Published 20 October, 2026

Vol. 114, Iss. 7 — 1 October 2026

Received 6 June 2026
Accepted 28 September 2026

DOI: https://doi.org/10.1103/hs3z-6tnr

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Searching for lepton flavor violating decays of the Higgs boson into $μ τ$ , $e τ$ , and $e μ$ final states at FCC-ee

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Searching for lepton flavor violating decays of the Higgs boson into μτ, eτ, and eμ final states at FCC-ee

Abstract

Physics Subject Headings (PhySH)

Article Text

References (64)

Searching for lepton flavor violating decays of the Higgs boson into $μ τ$ , $e τ$ , and $e μ$ final states at FCC-ee