Studies of the simultaneous measurement of the associated production of single top quarks and top quark pairs with a Z boson in trileptonic final states with ATLAS

This thesis deals with the simultaneous measurement of the single top quark and top quark pair in association with a $Z$ boson. Therefore, only events with trileptonic final states are considered. Furthermore, an artificial neural network is used, in order to separate the single top quark and top quark pair in association with a $Z$ boson and background events from each other, so that the uncertainties are decreased. The measured sensitivity for the production of single top quarks in association with a $Z$ boson is $\pm 0.15\,(\mathrm{stat.})\, ^{+0.37}_{-0.16}(\mathrm{syst.})$, whereas for the top quark pairs in association with a $Z$ boson, the sensitivity is $\pm 0.06\,(\mathrm{stat.})\pm 0.03\,(\mathrm{syst.})$.