Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s = 13 TeV

Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the bb̅bb̅, bb̅τ+τ− and bb̅γγ decay channels with single-Higgs boson analyses targeting the γγ, ZZ^∗, WW^∗, τ⁺τ⁻ and bb̅ decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton−proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126−139 fb⁻¹. The combination of the double-Higgs analyses sets an upper limit of μ_HH<2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λ_HHH), values outside the interval −0.4 < κ_λ=(λ_HHH/λ^SM_HHH)<6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles.