Search for Higgs Boson Pair Production in the bb̅bb̅ Final State from pp Collisions at √s̅ = 8 TeV with the ATLAS Detector

A search for Higgs boson pair production pp → hh is performed with 19.5 fb⁻¹ of proton-proton collision data at √s̅ = 8 TeV, which were recorded by the ATLAS detector at the Large Hadron Collider in 2012. The decay products of each Higgs boson are reconstructed as a high-momentum bb̅ system with either a pair of small-radius jets or a single large-radius jet, the latter exploiting jet substructure techniques and associated b-tagged track-jets. No evidence for resonant or non-resonant Higgs boson pair production is observed. The data are interpreted in the context of the Randall-Sundrum model with a warped extra dimension as well as the two-Higgs-doublet model. An upper limit on the cross-section for pp → G_{KK}^→ hh → bb̅bb̅ of 3.2 (2.3) fb is set for a Kaluza-Klein graviton G_{KK}^ mass of 1.0 (1.5) TeV, at the 95% confidence level. The search for non-resonant Standard Model hh production sets an observed 95% confidence level upper limit on the production cross-section σ(pp → hh → bb̅bb̅) of 202 fb, compared to a Standard Model prediction of σ(pp → hh → bb̅bb̅) = 3.6 ± 0.5 fb.