A Boost to $h\to Z\gamma$: from LHC to Future $e^{+}{e}^{-}$ Colliders

Abstract

A precise measurement of the Higgs $h\to Z\gamma$ decay is very challenging at the LHC, due to the very low %SM $h\to Z\gamma (Z\to \ell \ell )$ branching fraction and the shortage of kinematic handles to suppress the large SM $Z\gamma$ background. We show how such a measurement would be significantly improved by considering Higgs production in association with a hard jet. We compare the prospective HL-LHC sensitivity in this channel with other Higgs production modes where $h$ is fairly boosted, e.g.~weak boson fusion, and also to the potential $h\to Z\gamma$ measurement achievable with a future $e^{+}{e}^{-}$ circular collider ({\sl fcc-ee}). Finally, we discuss new physics implications of a precision measurement of $h\to Z\gamma$.

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