Combination of searches for Higgs boson pair production in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper combines multiple searches for Higgs boson pair production at 13 TeV using ATLAS data, setting upper limits on production rates and constraining Higgs self-coupling and quartic couplings with the most stringent bounds to date.

Contribution

It provides the first combined analysis of Higgs pair production searches at 13 TeV with ATLAS, improving constraints on Higgs couplings and effective field theory parameters.

Findings

Upper limit on Higgs pair production rate is 2.9 times the SM prediction.

Constraints on Higgs self-coupling modifier are -1.2 to 7.2 at 95% CL.

Constraints on quartic $HHVV$ coupling are 0.6 to 1.5 at 95% CL.

Abstract

This Letter presents results from a combination of searches for Higgs boson pair production using 126$-$140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV 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 $\kappa_{\lambda}=\lambda_{HHH}/\lambda_{HHH}^\mathrm{SM}$, and the quartic $HHVV$ coupling modifier $\kappa_{2V}=g_{HHVV}/g_{HHVV}^\mathrm{SM}$, are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are $-1.2 < \kappa_{\lambda} < 7.2$ and $0.6 < \kappa_{2V} < 1.5$, respectively, while the expected intervals are $-1.6 < \kappa_{\lambda} < 7.2$ and $0.4 < \kappa_{2V} < 1.6$ 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.