Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ final state in pp collisions at √s = 13 TeV with the ATLAS detector

A search for nonresonant Higgs boson pair production in the b¯bγγ final state
is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV
recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes
and expands upon the previous nonresonant ATLAS results in this final state based on the
same data sample. The analysis strategy is optimised to probe anomalous values not only of
the Higgs (H) boson self-coupling modifier κλ but also of the quartic HHV V (V = W, Z)
coupling modifier κ2V . No significant excess above the expected background from Standard
Model processes is observed. An observed upper limit μHH < 4.0 is set at 95% confidence
level on the Higgs boson pair production cross-section normalised to its Standard Model
prediction. The 95% confidence intervals for the coupling modifiers are −1.4 < κλ < 6.9 and
−0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are
fixed to the Standard Model predictions. The results are interpreted in the Standard Model
effective field theory and Higgs effective field theory frameworks in terms of constraints on
the couplings of anomalous Higgs boson (self-)interactions.