Methodology for EFT interpretation of Higgs boson Simplified Template Cross-section results in ATLAS

The Standard Model Effective Field Theory (EFT) expansion provides a general framework to report deviations between measurements and Standard model predictions. This framework can be used in the context Higgs coupling measurements, where ATLAS results are usually reported in terms of Simplified Template Cross-sections (STXS). This note describes techniques developed to interpret the STXS measurements within the framework of the EFT. Parameterizations of the impact on the Higgs sector of BSM phenomena introduced as EFT are developed, both for the Higgs boson production cross sections and decay widths. Techniques are presented to determine the combinations of EFT parameters to which the measurements provide sensitivity, accounting for measurement correlations, and to identify and treat directions in the space of the EFT parameters to which the measurements are not sensitive.