Hadronic top-quark pair production in association with two jets at Next-to-Leading Order QCD

TL;DR

This work provides a complete next-to-leading order QCD calculation for top-quark pair production in association with two jets at both the Tevatron and the LHC. Using an automated Helac-NLO framework, the authors compute integrated and differential cross sections, including the first NLO study of the Tevatron forward-backward top asymmetry. The results show negative, moderate NLO corrections and substantially reduced scale uncertainties, with notable distortions in differential distributions, especially in tails. The study enhances the precision of background modeling for Higgs and new-physics searches and demonstrates the efficacy of the Helac-NLO toolchain for complex multi-jet processes.

Abstract

We report on the calculation of the next-to-leading order QCD corrections to the production of ttbar pairs in association with two hard jets at the Fermilab TeVatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the TeVatron and 15% for the LHC. In case of the TeVatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to A_FB = -10.3% at leading order and A_FB = -4.6% at next-to-leading order. All results presented in this paper have been obtained with the help of the HELAC-NLO package.

Figures (18)

• Figure 1: A representative set of Feynman diagrams contributing to the LO hadronic $t\bar{t}jj$ production at ${\cal{O}}(\alpha_{s}^4)$. Double brown lines correspond to top quarks, single lines to light quarks and wiggly ones to gluons.
• Figure 2: A representative set of Feynman diagrams contributing to the virtual corrections to hadronic $t\bar{t}jj$ production at ${\cal{O}}(\alpha_{s}^5)$. Double brown lines correspond to top quarks, single lines to light quarks and wiggly ones to gluons.
• Figure 3: Differential cross section distributions as a function of rapidity, $y_t$, of the top and anti-top quark at LO (upper panel) and NLO (lower panel) for $p\bar{p} \to t \bar{t} jj + X$ production at the TeVatron run II with $\sqrt{s}= 1.96 ~\textnormal{TeV}$. The (orange) solid curve corresponds to the top quark, whereas the (brown) dashed one to the anti-top quark.
• Figure 4: Differential charge asymmetry, $A(y_t)$, as a function of the (anti-)top quark rapidity at LO (upper panel) and NLO (lower panel) for $p\bar{p} \to t \bar{t} jj + X$ production at the TeVatron run II with $\sqrt{s}= 1.96 ~\textnormal{TeV}$. $NLO_{1}$ refers to a result with a consistent expansion in $\alpha_s$, while $NLO_{2}$ to the unexpanded one.
• Figure 5: Differential cross section distributions as a function of the rapidity of the top (left panel) and anti-top (right panel) for $p\bar{p} \to t \bar{t} jj + X$ production at the TeVatron run II with $\sqrt{s}= 1.96 ~\textnormal{TeV}$. The dash-dotted curve corresponds to the LO, whereas the solid one to the NLO result. The uncertainty bands depict scale variation. The lower panels display the differential $\cal K$ factor.