Measurements of ttbar pairs produced in association with electroweak gauge bosons using the ATLAS detector

The large centre-of-mass energy available at the proton-proton collider LHC allows for the copious production of top-quark-antiquark pairs in association with electroweak gauge bosons (W / Z / gamma) at high transverse momenta. The tt ̄Z and tt ̄W production cross sections are simultaneously measured using a combined fit in several analysis regions. The measurement of the tt ̄Z cross section is used to set constraints on effective field theory operators which modify the tt ̄Z vertex. The ttgamma measurements are performed in single-lepton and dilepton final states in a fiducial volume. The differential cross-sections are measured as a function of several photon kinematic variables.