The top portal to new physics

This thesis with the titel ''The top portal to new physics'' is about the search for processes that are not described by the current theory of particle physics. The heaviest known elementary particle, the top quark, is investigated if it could be a portal to new physics. The quest for the origin of the asymmetry between matter and anti-matter in the universe is the main motivation for this work. Data collected with the ATLAS detector in the years 2015 until 2018 is used to study the top quark. As the top decays, it conveys all its spin information to its decay products. As a result, distributions of spin correlated observables are analysed to provide sensitivity to the production and/or decay mechanism of the top quark. The framework of Effective Field Theory (EFT) is exploited to predict the deviations in the observed distributions. The EFT is model independent, but adds mathematical structures to the SM that become increasingly manifest at high energy scales. One such structure is the operator OtW, which is of paramount interest as it could cause an asymmetry between matter and anti-matter.