$HH$ non-resonant and self-coupling at ATLAS+CMS

Measuring Higgs pair production (HH) will provide information about the Higgs self coupling, which is key to determine the shape of the Higgs potential at higher order. The leading HH production mode at the Large Hadron Collider is gluon gluon fusion and the sub-leading production mode is vector boson fusion. Given the small cross section, Higgs pair production has not yet been observed. However, competitive upper limits to the HH production cross section and Higgs self coupling modifier κλ are set by the ATLAS and CMS Collaborations. Searches for HH production in a final state where one Higgs boson decays to a pair of b quarks, and the other Higgs boson decays either to two photons, two b quarks or four leptons, with the full Run 2 proton-proton collision data set at √s = 13 TeV from the ATLAS and CMS experiments, are presented. Combinations of HH searches and Higgs self coupling measurements with partial Run 2 data are also presented. Competitive upper limits on the HH cross section are obtained by the ATLAS and CMS HH searches in the bbγγ final state. However, the CMS HH search in the bbbb final state sets the current most stringent observed upper limit on the HH production cross section of 3.6 times the Standard Model expectation at 95% confidence level. The current most stringent limits on κλ are obtained by the ATLAS HH search in the bbγγ final state, which sets observed (expected) limits of −1.5 (−2.4) < κλ < 6.7 (7.7) at 95% confidence level.