The electroweak contribution to the top quark forward-backward asymmetry at the Tevatron

TL;DR

This paper calculates electroweak effects on the top-quark forward-backward asymmetry at the Tevatron, showing they increase the Standard Model prediction and reduce the discrepancy with experimental data, but a significant deviation remains.

Contribution

It provides a detailed calculation of electroweak contributions to the asymmetry, combining them with QCD effects, which was not previously done with this level of detail.

Findings

Electroweak contributions are a significant fraction of QCD asymmetry.

Including electroweak effects reduces the observed deviation from the Standard Model.

A 3-sigma deviation persists for high invariant-mass cuts.

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.