Measuring $hhWW$ Coupling at Lepton Colliders

The quartic Higgs-gauge-boson coupling $g_{hhWW}$ is sensitive to the electroweak symmetry breaking mechanism, however, it is challenging to be measured at the large hadron collider. We show that the coupling can be well probed at future lepton colliders through di-Higgs boson production via the vector boson fusion channel. We perform a detailed simulation of $\ell^+\ell^-\to \nu\bar\nu hh\to 4b\,+ \!\!\not{\!\! E}_T$ with parton showering effects at $e^+e^-$, $\mu^+\mu^-$ and $e^-\mu^+$ colliders. We find that the regions of $g_{hhWW}/g_{hhWW}^{\rm SM}<0.86$ and $g_{hhWW}/g_{hhWW}^{\rm SM}>1.32$ can be discovered at the $5\sigma$ confidence level at the 10 TeV $\mu^+ \mu^-$ collider with an integrated luminosity of 3 ab$^{-1}$.