A robust search for lepton flavour violating axions at Mu3e

Abstract We propose a search at Mu3e for lepton flavor violating axion(-like) particles in μ → 3e + a decays. By requiring an additional e + e − pair from internal conversion, one can circumvent the calibration challenges which plague the μ → e + a channel for axions lighter than 20 MeV. Crucially,...

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Bibliographic Details
Main Authors: Simon Knapen, Kevin Langhoff, Toby Opferkuch, Diego Redigolo
Format: Article
Language:English
Published: SpringerOpen 2025-07-01
Series:Journal of High Energy Physics
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Online Access:https://doi.org/10.1007/JHEP07(2025)243
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Summary:Abstract We propose a search at Mu3e for lepton flavor violating axion(-like) particles in μ → 3e + a decays. By requiring an additional e + e − pair from internal conversion, one can circumvent the calibration challenges which plague the μ → e + a channel for axions lighter than 20 MeV. Crucially, the corresponding reduction in signal rate is to a large extent compensated for by Mu3e’s ability to resolve highly collimated tracks. For phase I of Mu3e, we project a sensitivity to decay constants as high as 6 × 109 GeV which probes uncharted parameter space in scenarios of axion dark matter. The sensitivity to axions which couple primarily to right-handed leptons can be further improved by leveraging the polarisation of the muon beam.
ISSN:1029-8479