Effective Field Theory Interpretation of ATLAS Top Quark Measurements

Abstract:In the first part of this dissertation, the combination of ATLAS top quark mea-surements to constrain dimension-six operator coefficients is presented. Top quark measurements provide a powerful tool to constrain the electroweak interaction of top quarks. Many models of physics Beyond the Standard Model (BSM) predict deviations of top quark interactions from the Standard Model. The Standard Model Effective Theory (SMEFT) provides a framework to parameterize BSM effects in a model independent way. Combining top quark measurements allows to constrain several Wilson coefficients of the dimension-six SMEFT operators at once. Specifi-cally, the combination of the √s = 8 TeV t-channel single top cross section, the W helicity fractions and the single top decay distributions is studied. This allows to constrain a set of five Wilson coefficients, four of which generate modifications to the W tb interaction vertex and one four-quark operator. Systematic uncertainties are correlated between the measurements and these correlations are calculated and included in the combination. Limits are set simultaneously on all Wilson coefficients as well as individually. All limits are in accordance with Standard Model predictions.