Effective field theory interpretations of the search for HH bb with 308 fb^-1 of data collected at s = 13 TeV and 13. 6 TeV with the ATLAS detector

This note presents interpretations of a search for Higgs boson pair production in the bb final state using the Standard Model Effective Field Theory (SMEFT) and Higgs Effective Field Theory (HEFT) frameworks. The search uses 140 fb^-1 and 168 fb^-1 of pp collision data at s = 13 TeV and 13. 6 TeV, respectively, collected by the ATLAS detector at the Large Hadron Collider. Modifications to the gluon-gluon fusion and vector-boson fusion production cross sections induced by dimension-6 SMEFT operators and HEFT operators are considered. Modifications to the Higgs boson decay branching fractions in the presence of EFT operators are also included. One-dimensional constraints at the 95\% confidence level are derived for individual SMEFT operators in the linear and linear-plus-quadratic parameterizations. In HEFT, one and two-dimensional constraints at the 95\% confidence level are derived for individual operators and pairs of operators. These HEFT constraints are additionally derived while profiling other Wilson coefficients to their best-fit values. All results are consistent with the Standard Model predictions and provide insights into the validity of the SMEFT expansion and correlations among HEFT operators.