NLO QCD corrections to t(t)over-barb(b)over-bar production at the LHC: 2. Full hadronic results

We present predictions for t (t) over barb (b) over bar production at the LHC in next-to-leading order QCD. The precise description of this background process is a prerequisite to observe associated t (t) over barH production in the H -> b (b) over bar decay channel and to directly measure the top-quark Yukawa coupling at the LHC. The leading-order cross section is extremely sensitive to scale variations. We observe that the traditional scale choice adopted in ATLAS simulations underestimates the t (t) over barb (b) over bar background by a factor two and introduce a new dynamical scale that stabilizes the perturbative predictions. We study various kinematic distributions and observe that the corrections have little impact on their shapes if standard cuts are applied. In the regime of highly boosted Higgs bosons, which offers better perspectives to observe the t (t) over barH signal, we find significant distortions of the kinematic distributions. The one-loop amplitudes are computed using process-independent algebraic manipulations of Feynman diagrams and numerical tensor reduction. We find that this approach provides very high numerical stability and CPU efficiency.