Combination of searches for Higgs boson pairs in proton-proton collisions at sqrt(s) = 13 TeV with the ATLAS detector

This letter presents a combination of searches for Higgs boson pair production using up to 36.1\( \text{fb}^{−1} \) of proton-proton collision data at a centre-of-mass energy \( \sqrt{\text{s}} \)=13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the \( \text{b}\bar{\text{b}} \text{b}\bar{\text{b}} \), \( \text{b}\bar{\text{b}} \text{WW} \), \( \text{b}\bar{\text{b}} \tau\tau \), \( \text{WWWW} \), \( \text{b}\bar{\text{b}}\gamma\gamma \) and \( \text{WW} \gamma\gamma \) final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. The combined observed limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 times the predicted Standard Model cross-section. Limits are also set on the ratio (\( \kappa_{\lambda} \)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level to −5.0<\( \kappa_{\lambda} \)<12.0. In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model.