Double Higgs boson production and Higgs self-coupling extraction at CLIC

The Compact Linear Collider (CLIC) is a future electron–positron collider that will allow measurements of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies from $\sqrt{s}$ = 1.4 to 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$. It is enhanced by including the cross-section measurement of ZHH production at 1.4 TeV. The expected sensitivity of CLIC for Higgs pair production through W-boson fusion is studied for the decay channels $\mathrm{b}\bar{\mathrm{b}}\mathrm{b}\bar{\mathrm{b}}$ and $\mathrm{b}\bar{\mathrm{b}}\mathrm{W}\mathrm{W}^{*}$ using full detector simulation including all relevant backgrounds at $\sqrt{s}$ = 1.4 TeV with an integrated luminosity of $\mathcal {L}$ = 2.5 ab$^{-1}$ and at $\sqrt{s}$ = 3 TeV with $\mathcal {L}$ = 5 ab$^{-1}$. Combining $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$ and ZHH cross-section measurements at 1.4 TeV with differential measurements in $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$ events at 3 TeV, CLIC will be able to measure the trilinear Higgs self-coupling with a relative uncertainty of $-8\%$ and $ +11\%$ at 68% C.L., assuming the Standard Model. In addition, prospects for simultaneous constraints on the trilinear Higgs self-coupling and the Higgs-gauge coupling HHWW are derived based on the ${\text {H}\text {H}\nu \bar{\nu }}$ measurement.