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arXiv · 2212.02818

Testing axion couplings to leptons in $Z$ decays at future $e^+e^-$ colliders

Lorenzo Calibbi·Zijie Huang·Shaoyang Qin·Yiming Yang·Xiaoyue Yin
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Abstract

We study the possibility of probing the existence of a light, invisible, axion-like particle (ALP) $a$ in leptonic decays of the $Z$ boson at the proposed high-energy $e^+e^-$ colliders, CEPC and FCC-ee. Both projects plan to run at the $Z$ pole, collecting $10^{12}-10^{13}$ visible $Z$ decays. We show that, searching for the emission of an invisible ALP from leptons in leptonic $Z$ decays, this enormous statistics could allow to constrain the ALP couplings to leptons at an unprecedented level for laboratory experiments. In particular, within a Monte Carlo simulation framework, we estimate that CEPC/FCC-ee can be sensitive to the coupling of an invisible ALP to muons up to $f_a/C^A_{\mu\mu} \approx 1$ TeV - where $f_a$ is the ALP decay constant - corresponding to ${\rm BR}(Z \to \mu^+\mu^-\,a) \approx 3\times 10^{-11}$.

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Lorenzo Calibbi, Zijie Huang, Shaoyang Qin, Yiming Yang, Xiaoyue Yin. 2022-12-06. Testing axion couplings to leptons in $Z$ decays at future $e^+e^-$ colliders. https://doi.org/10.1103/physrevd.108.015002

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