Physical Review Letters, cilt.133, sa.10, 2024 (SCI-Expanded)
This Letter presents results from a combination of searches for Higgs boson pair production using Formula Presented of proton-proton collision data at Formula Presented recorded with the ATLAS detector. At 95% confidence level (CL), the upper limit on the production rate is 2.9 times the standard model (SM) prediction, with an expected limit of 2.4 assuming no Higgs boson pair production. Constraints on the Higgs boson self-coupling modifier Formula Presented, and the quartic Formula Presented coupling modifier Formula Presented, are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are Formula Presented and Formula Presented, respectively, while the expected intervals are Formula Presented and Formula Presented in the SM case. Constraints obtained for several interaction parameters within Higgs effective field theory are the strongest to date, offering insights into potential deviations from SM predictions.