Top quark pair production and decay at hadron colliders

TL;DR

Bernreuther et al. perform a comprehensive NLO QCD study of top-quark pair production and decay at hadron colliders with full spin correlations. They derive analytic differential cross sections for $q\bar{q}$ and $gg$ production, include real emission and mass-factorization, and merge these with polarized top-quark decay densities to obtain spin-density matrices for $t\bar{t}$ in hadronic collisions. The paper shows that spin-induced angular distributions in dilepton, lepton+jets, and all-jet channels are sizable and largely robust against non-factorizable corrections, with practical fit functions provided for experimental use. Numerical results reveal pronounced spin correlations at the Tevatron and especially at the LHC, where the helicity basis offers the strongest signals; these results also exhibit notable dependence on PDFs and reduced theoretical uncertainties after NLO corrections.

Abstract

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.

Figures (6)

• Figure 1: Left: Scaling functions $f^{(0)}_{q\bar{q}}(\eta)$ (dotted), $f^{(1)}_{q\bar{q}}(\eta)$ (full), and $\tilde{f}^{(1)}_{q\bar{q}}(\eta)$ (dashed). Right: The same for the process $gg\to t\bar{t}(g)$.
• Figure 2: Left: Scaling functions $g^{(0)}_{q\bar{q},1} (\eta)$ (dotted), $g^{(1)}_{q\bar{q},1}(\eta)$ (full), and $\tilde{g}^{(1)}_{q\bar{q},1}(\eta)$ (dashed). Right: The same for the process $gg\to t\bar{t}(g)$.
• Figure 3: Left: Scaling functions $g^{(0)}_{q\bar{q},2} (\eta)$ (dotted), $g^{(1)}_{q\bar{q},2}(\eta)$ (full), and $\tilde{g}^{(1)}_{q\bar{q},2}(\eta)$ (dashed). Right: The same for the process $gg\to t\bar{t}(g)$.
• Figure 4: Left: Scaling functions $g^{(0)}_{q\bar{q},3} (\eta)$ (dotted), $g^{(1)}_{q\bar{q},3}(\eta)$ (full), and $\tilde{g}^{(1)}_{q\bar{q},3}(\eta)$ (dashed). Right: The same for the process $gg\to t\bar{t}(g)$.
• Figure 5: Left: Scaling functions $g^{(0)}_{q\bar{q},4} (\eta)$ (dotted), $g^{(1)}_{q\bar{q},4}(\eta)$ (full), and $\tilde{g}^{(1)}_{q\bar{q},4}(\eta)$ (dashed). Right: The same for the process $gg\to t\bar{t}(g)$.