Fig. 6: Limits on the Higgs boson self-interaction and quartic coupling.
From: A portrait of the Higgs boson by the CMS experiment ten years after the discovery
Combined expected and observed 95% CL upper limits on the HH production cross-section for different values of κλ (left) and κ2V (right), assuming the SM values for the modifiers of Higgs boson couplings to top quarks and vector bosons. The green and yellow bands represent the 1-s.d. and 2-s.d. extensions beyond the expected limit, respectively; the red solid line (band) shows the theoretical prediction for the HH production cross-section (its 1-s.d. uncertainty). The areas to the left and to the right of the hatched regions are excluded at the 95% CL.
