Next-to-leading order QCD predictions for top-quark pair production with up to two jets merged with a parton shower

Abstract

We present differential cross sections for the production of top-quark pairs in conjunction with up to two jets, computed at next-to leading order in perturbative QCD and consistently merged with a parton shower in the Sherpa+OpenLoops framework. Top quark decays including spin correlation effects are taken into account at leading order accuracy. The calculation yields a unified description of top-pair plus multi-jet production, and detailed results are presented for various key observables at the Large Hadron Collider. A large improvement with respect to the multi-jet merging approach at leading order is found for the total transverse energy spectrum, which plays a prominent role in searches for physics beyond the Standard Model.

Figures (3)

• Figure 1: Differential $k_\perp$ jet resolutions calculated from all partons (excluding top quarks) without any restrictions on their phase-space in a calculation with stable top final states. Solid lines indicate the MEPS@NLO prediction for three different values of the merging scale, $Q_\text{cut}=$ 20 GeV (blue), 30 GeV (red), and 40 GeV (green). They are contrasted with the combined $\mu_R$-$\mu_F$-$\mu_Q$-uncertainties of the central MEPS@NLO (orange full band) and MEPS@LO (blue hatched band) predictions. The center ratio highlights the $Q_\text{cut}$-variation only, while the lower ratio details the relative contributions of the individual matched $pp\to t\bar{t}+n\,\text{jets}$ calculations and how they vary with $Q_\text{cut}$. Statistical uncertainties are indicated by error bars.
• Figure 2: Light-flavor jet multiplicity distribution (including $c$- but not $b$-jets) for transverse momentum thresholds of 40, 60 and 80 GeV \ref{['fig:jet_multi']} and transverse momentum spectra of the three leading light-flavor jets \ref{['fig:jet_pt']}. Solid (red) lines indicate MEPS@NLO predictions, and the full (orange) band shows the corresponding total theoretical uncertainty. Dashed lines indicate MEPS@LO predictions, with the corresponding uncertainties shown as hatched (blue) bands. S--MC@NLO predictions are shown as dotted histograms. Statistical uncertainties for each calculation are indicated by error bars.
• Figure 3: Transverse momentum of the reconstructed top quark \ref{['fig:top_pt']} and total transverse energy \ref{['fig:ht']}, see Fig. \ref{['fig:fig2']} for details. The lower ratio details the contributions of the individual matched $pp\to t\bar{t}+n\,\text{jets}$ calculations.