We present predictions for the production cross section of a standard model $Z^0$ boson in association with a $t\overline{t}$ pair at the next-to-leading order accuracy in QCD, matched with shower Monte Carlo programs to evolve the system down to the hadronization energy scale. We adopt a framework based on three well-established numerical codes, namely, the powheg-box, used for computing the cross section, helac-nlo, which generates all necessary input matrix elements, and finally a parton shower program, such as pythia or herwig, which allows for including $t$-quark and $Z^0$-boson decays at leading-order accuracy and generates shower emissions, hadronization and hadron decays.

• Received 22 December 2011

DOI:https://doi.org/10.1103/PhysRevD.85.074022