Constraining the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at sqrt(s) = 13 TeV

Constraints on the Higgs boson self-coupling are set by combining the double-Higgs boson analyses with the single-Higgs boson analyses. The data used by these analyses were recorded by the ATLAS detector at the LHC in proton-proton collisions at sqrt(s) = 13 TeV and corresponds to an integrated luminosity of 126-139/fb. The combination of the double-Higgs analyses sets an upper limit at 95% confidence level on the production cross section of this process normalised to its Standard Model (SM) prediction mu(HH) < 2.4. Combining the single-Higgs and double-Higgs analysis, with the assumption that new physics affects only the Higgs boson self-coupling (Lambda(HHH) values outside the interval -0.4 < kLambda = Lambda(HHH)/Lambda(HHH)_SM < 6.3 are excluded at 95% confidence level. This analysis provides the most stringent constraints on Higgs boson self-interactions to date.