# Combination of searches for Higgs boson pairs 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 with the ATLAS detector, setting limits on production cross-sections, Higgs self-coupling, and new physics models, with no significant excess observed.

## Contribution

It provides the first combined analysis of various Higgs pair decay channels at 13 TeV, improving constraints on Higgs self-coupling and new physics scenarios.

## Key findings

- No significant excess above Standard Model predictions.
- Limits set on Higgs pair production cross-section and self-coupling.
- Constraints on new physics models like resonances and extra dimensions.

## Abstract

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy $\sqrt{s} = 13$ TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bbbb, bbWW, bb$\tau\tau$, WWWW, bb$\gamma \gamma$ and WW$\gamma\gamma$ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) 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 in observation (expectation) to $ -5.0 < \kappa_{\lambda} <12.0 $ ($ -5.8 < \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.