We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular e+e-\documentclass[12pt]{minimal}
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\begin{document}$$e^+e^-$$\end{document}collider (FCC-ee) in the process e+e-→HZ\documentclass[12pt]{minimal}
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\begin{document}$$e^+e^-\rightarrow HZ$$\end{document} with Z→ℓ+ℓ-\documentclass[12pt]{minimal}
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\begin{document}$$Z\rightarrow \ell ^+\ell ^-$$\end{document} (ℓ=e\documentclass[12pt]{minimal}
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\begin{document}$$\ell =e$$\end{document} or μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document}) using an integrated luminosity of 3.5 ab-1\documentclass[12pt]{minimal}
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\begin{document}$$^{-1}$$\end{document} at a center-of-mass energy s=240\documentclass[12pt]{minimal}
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\begin{document}$$\sqrt{s}=240$$\end{document} GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. The minimum branching ratio for a 5σ\documentclass[12pt]{minimal}
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\begin{document}$$5\sigma $$\end{document} observation after 3.5 ab-1\documentclass[12pt]{minimal}
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\begin{document}$$^{-1}$$\end{document} of data taking is 1.7±0.1%(stat+syst)\documentclass[12pt]{minimal}
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\begin{document}$$1.7\pm 0.1\%(stat+syst) $$\end{document}. The branching ratio exclusion limit at 95% CL is 0.63±0.22%((stat+syst))\documentclass[12pt]{minimal}
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\begin{document}$$0.63 \pm 0.22\%((stat+syst))$$\end{document}.
