Seminarium Teorii Oddziaływań Elementarnych

I will present a study of the production of top quark pairs in association with one hard jet in the di-lepton decay channel at NLO in QCD. All resonant and non-resonant contributions are fully taken into account in these calculations, including irreducible backgrounds to ttj production, interferences and off-shell effects of the top quark and the W gauge boson. I will show predictions for the LHC Run II with a center-of-mass energy of 13 TeV and extensively investigate the dependence of these results upon variation of renormalisation and factorisation scales and parton distribution functions in the quest for an accurate estimate of the theoretical uncertainties. Additionally, I will explore a few possibilities for a dynamical scale choice with the goal of stabilising the perturbative convergence of the differential cross sections far away from the tt threshold. Results that I will present are particularly relevant for searches of new physics as well as for precise measurements of the top-quark fiducial cross sections and top-quark properties at the LHC.