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Abstract:We perform the resummation of soft-gluon emissions for squark and gluino production at next-to-next-to-leading logarithmic (NNLL) accuracy. We include also the one-loop hard matching coefficients as well as Coulomb corrections to second order, using Mellin-moment methods. We study the characteristics of this resummation in detail for a centre-of-mass (CM) energy of 8 TeV at the LHC, and for squark and gluino masses up to 2.5 TeV. We find significant enhancing effects for all four processes of squark-and gluinopair production. Scale dependence is generally reduced compared to NLL resummation, except for gluino-pair production where we find a moderate enhancement.

We present theoretical predictions for selected differential cross sections for the process $$pp \rightarrow t {\bar{t}}B$$pp→tt¯B at the LHC, where B can be a Higgs (H), a Z or a W boson. The predictions are calculated in the direct QCD framework up to the next-to-next-leading logarithmi accuracy and matched to the complete NLO results including QCD and electroweak effects. Additionally, results for the total cross sections are provided. The calculations deliver a significant improvement of the theoretical predictions, especially for the $$ t {\bar{t}}H$$tt¯H and the $$ t {\bar{t}}Z$$tt¯Z production. In these cases, predictions for both the total and differential cross sections are remarkably stable with respect to the central scale choice and carry a substantially reduced scale uncertainty in comparison with the complete NLO predictions.

We perform threshold resummation of soft gluon corrections to the total cross sections and the invariant mass distributions for production of a top-antitop quark pair associated with a heavy electroweak boson V = W + , W − or Z in pp collisions at the Large Hadron Collider. The resummation is carried out at next-to-next-toleading-logarithmic (NNLL) accuracy using the direct QCD Mellin space technique in the three-particle invariant mass kinematics. It is found that for the ttZ process the soft gluon resummation introduces significant corrections to the next-to-leading order (NLO) results. For the central scale equal to the ttZ invariant mass the corrections reach nearly 30%. For this process, the dominant theoretical uncertainty of the cross section due to the scale choice is significantly reduced at the NLO+NNLL level with respect to the NLO results. The effects of resummation are found to be less pronounced in the ttW ± case. The obtained results are compared to recent measurements performed by CMS and ATLAS collaborations at the LHC. 1 anna.kulesza@uni-muenster.de 2