Abstract
This letter presents a combination of searches for Higgs boson pair production using up to 36.1fb−1 of proton–proton collision data at a centre-of-mass energy 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 bb¯bb¯, bb¯W+W−, bb¯τ+τ−, W+W−W+W−, bb¯γγ and W+W−γγ 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 (κλ) 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<κλ<12.0 (−5.8<κλ<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.
Highlights
The discovery of the Higgs boson (H ) [1,2] at the Large Hadron Collider (LHC) [3] in 2012 has experimentally confirmed the Brout– Englert–Higgs (BEH) mechanism of electroweak symmetry breaking and mass generation [4,5,6]
The Standard Model (SM) H H analyses use signal samples generated at next-toleading order (NLO) in QCD with Madgraph5_aMC@NLO [59] using the CT10 NLO parton distribution function (PDF) set [60]
For k/MPl = 1, the subleading systematic uncertainties come from b-tagging at low GKK mass, that affect the limit by 3%, and from jet energy scale and resolution at high mass, that affect the upper limit by 2% (3%) at 1 TeV (3 TeV)
Summary
The discovery of the Higgs boson (H ) [1,2] at the Large Hadron Collider (LHC) [3] in 2012 has experimentally confirmed the Brout– Englert–Higgs (BEH) mechanism of electroweak symmetry breaking and mass generation [4,5,6]. Observing the production of Higgs boson pairs (H H ) and measuring the Higgs boson self-coupling λH H H is a crucial validation of the BEH mechanism. In the SM, the gluon–gluon fusion pp → H H process (ggF) accounts for more than 90% of the Higgs boson pair production cross-section, and only this production mode is considered here The Higgs boson self-coupling is discussed in the context of BSM models in Refs. Several BSM models predict the existence of heavy particles decaying into a pair of Higgs bosons.
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