Charge asymmetry of heavy quarks at hadron colliders

TL;DR

The paper addresses the charge asymmetry in heavy-quark production at hadron colliders, showing that radiative QCD corrections induce a forward-backward–like difference between heavy quarks and antiquarks. It analyzes the partonic sources, highlighting the antisymmetric interference in $q\bar{q}\to Q\bar{Q}$ and related $qg$-initiated processes, and relates the QCD structure to a QED-like canonical form via the color factor $d_{abc}^2$. By folding with parton distributions, the authors predict a Tevatron forward-backward asymmetry of about 4.6–5.8% and region-dependent asymmetries at the LHC, while noting large LO uncertainties due to missing NLO corrections. The work provides a framework to test QCD production dynamics and informs analyses of top- and bottom-quark production in current and future collider experiments.

Abstract

A sizeable difference in the differential production cross section of top and antitop quarks, respectively, is predicted for hadronically produced heavy quarks. It is of order $α_s$ and arises from the interference between charge odd and even amplitudes respectively. For the TEVATRON it amounts up to 15\% for the differential distribution in suitable chosen kinematical regions. The resulting integrated forward-backward asymmetry of 4--5\% could be measured in the next round of experiments. At the LHC the asymmetry can be studied by selecting appropriately chosen kinematical regions. Furthermore, a slight preference at LHC for centrally produced antitop is predicted, with top quarks more abundant at large positive and negative rapidities.

Figures (14)

• Figure 1: Origin of the QCD charge asymmetry in hadroproduction of heavy quarks: interference of final-state (a) with initial-state (b) gluon bremsstrahlung plus interference of the box (c) with the Born diagram (d). Only representative diagrams are shown.
• Figure 2: Origin of the QCD charge asymmetry in hadroproduction of heavy quarks through flavor excitation.
• Figure 3: Cut diagrams.
• Figure 4: Differential charge asymmetry in top quark pair production for fixed partonic center of mass energies $\sqrt{\hat{s}}=400$ GeV (solid), $600$ GeV (dashed) and $1$ TeV (dotted). We also plot the differential asymmetry for b-quarks with $\sqrt{\hat{s}}=400$ GeV (dashed-dotted).
• Figure 5: Integrated charge asymmetry as a function of the partonic center of mass energy for top and bottom quark pair production.