Hadroproduction of ttbb final states at LHC: predictions at NLO accuracy matched with parton shower

We present predictions for the hadroproduction of ttbb final states at the LHC with collision energies root s = 8 TeV and 14 TeV at NLO accuracy matched with parton shower, as obtained with PowHel + PYTHIA. We quantify the effects of parton shower and hadronization. We find these are in general moderate except the effect of the decay of heavy particles, which can modify significantly some distributions, like that of the invariant mass of the two leading b-jets. We also show kinematic distributions obtained with cuts inspired to those recently employed by the CMS collaboration. For these predictions, we present the theoretical uncertainty bands, related to both scale and PDF variations. We find that these uncertainties are only moderately affected by the change of the collision energy.