Measurement of the ttZ cross section in the four lepton channel at 13 TeV with ATLAS

The production of a Z boson together with a top quark pair provides an important test of the standard model and can be used to measure the coupling between a top quark and a Z boson. So far the coupling has not yet directly been measured. A first probe of the coupling is the observation of the associated production of a top quark pair and a Z boson. The ttZ cross section has already been measured by ATLAS and CMS at 8 TeV. This poster shows the first results at 13 TeV in the four lepton channel. The current measurement with 3.2 fb-1 reaches about the same sensitivity as the 8 TeV one, at an increase of the ttZ cross section of about four. The four lepton channel is characterized by very pure signal regions but still limited by large statistical uncertainties.​