Renormalization-group improved fully differential cross sections for top pair production

We extend approximate next-to-next-to-leading order results for top-pair pro- duction to include the semi-leptonic decays of top quarks in the narrow-width approxima- tion. The new hard-scattering kernels are implemented in a fully dierential parton-level Monte Carlo that allows for the study of any IR-safe observable constructed from the mo- menta of the decay products of the top. Our best predictions are given by approximate NNLO corrections in the production matched to axed order calculation with NLO cor- rections in both the production and decay subprocesses. Being fully dierential enables us to make comparisons between approximate results derived via dierent (PIM and 1PI) kinematics for arbitrary distributions. These comparisons reveal that the renormalization- group framework, from which the approximate results are derived, is rather robust in the sense that applying a realistic error estimate allows us to obtain a reliable prediction with a reduced theoretical error for generic observables and analysis cuts.