Combination of Searches for Higgs Pair Production in pp collisions at √s=13 TeV with the ATLAS Detector

Searches for Higgs pair production (HH) are the only direct method of studying the Higgs self-interaction at the LHC. This talk will present the latest ATLAS HH combination results with the full Run 2 dataset of 139/fb at √s=13 TeV. By combining results from three different complementary search channels, bbγγ, bbττ, and bbbb, the HH combination is sensitive to new physics in both non-resonant and resonant interpretations. 

    In the non-resonant interpretation, bbγγ and bbττ channels are combined to produce limits on the Standard Model (SM) HH production cross-section and the Higgs boson self-coupling. Although no evidence for a signal was observed, the observed (expected) upper limits on SM HH production cross-section at 95% confidence level are 91.44 fb (92.10 fb). The combination of both channels also provides strong observed (expected) limits on Higgs self-coupling modifier, ??_??, between −1.0 ≤ ??_?? ≤ 6.6 (−1.2 ≤ ??_?? ≤ 7.2).

    For the resonant interpretation, bbγγ, bbττ, and bbbb, are combined to search for a heavy scalar decaying into two Higgs bosons with masses between 251 GeV - 3 TeV. Upper limits on the observed (expected) production cross-section are set ranging between 1.1 and 595 fb (1.2 and 393 fb).