Measurement of ttZ and ttW production at ATLAS in 13 TeV data, using trilepton and same charge dimuon final states

The production of ttZ serves as an important probe of the coupling of top quarks to Z bosons. Modifications to this coupling by physics beyond the Standard Model would have an effect on the ttZ production rates. The first measurements of ttZ production were performed in 8 TeV data by ATLAS and CMS. At 13 TeV collision energy, the production rate of ttZ increases by almost a factor of 4 and the effects of new physics, if present, should become more prominent. The first measurement by ATLAS of ttZ production at 13 TeV is presented here, with focus on the selection region that requires three charged leptons. This signature constitutes a compromise between a higher branching ratio for hadronic top decay chains and the better separation from background of the leptonic top decays. Moreover, the ttW process is measured in a simultaneous fit, using final states that contain either three charged leptons or two muons of the same charge. The first observation of ttW was performed by ATLAS using 8 TeV data. Measuring this process can probe several different models for physics beyond the Standard Model.