The electroweak contribution to the top quark forward-backward asymmetry at the Tevatron
Wolfgang Hollik, Davide Pagani
TL;DR
The paper addresses the discrepancy between the measured Tevatron top-quark forward-backward asymmetry and the Standard Model (SM) prediction by quantifying the electroweak contributions. It calculates EW effects at $O(\alpha^2)$ and $O(\alpha\alpha_s^2)$ and combines them with the QCD contribution across all relevant partonic channels, applying mass and rapidity cuts to compare with data. The authors find that EW terms provide a non-negligible fraction of the QCD-induced asymmetry with the same sign, thereby enlarging the SM prediction and reducing the observed deviation. Despite this improvement, for the high-invariant-mass region with $M_{t\bar{t}} > 450$ GeV, a $3$-sigma deviation from the QCD prediction persists, indicating that EW effects help but do not fully resolve the discrepancy.
Abstract
The electroweak contributions to the forward-backward asymmetry in the production of top-quark pairs at the Tevatron are evaluated at O(alpha^2) and O(alpha*alphas^2). We perform a detailed analysis of all partonic channels that produce an asymmetry and combine them with the QCD contributions. They provide a non-negligible fraction of the QCD-induced asymmetry with the same overall sign, thus enlarging the Standard Model prediction and diminishing the observed deviation. For the observed mass-dependent forward-backward asymmetry a 3-sigma deviation still remains at an invariant-mass cut of M_(t-tbar) > 450 GeV.