Quantum coherence, top transverse polarisation and the Tevatron asymmetry $A_{FB}^\ell$

TL;DR

This paper investigates how quantum coherence and top transverse polarisation significantly influence the forward-backward asymmetry in top quark pair production at the Tevatron, revealing overlooked interference effects.

Contribution

It demonstrates that interference between top helicity states and transverse polarisation effects are crucial for accurately predicting asymmetries, correcting previous underestimations.

Findings

Interference between helicity states greatly affects asymmetry calculations.

Transverse top polarisation is linked to interference effects.

Previous models underestimated asymmetries by factors of 50 to 2.

Abstract

We revisit the relation between the asymmetries $A_{FB}$ and $A_{FB}^\ell$ in $t \bar t$ production at the Tevatron, using as new physics benchmark a colour octet. We find that $A_{FB}^\ell$ receives large contributions from the interference between $\lambda = \pm 1/2$ top helicity states, which has been ignored in some of the previous literature on the subject. The omission of these contributions results in a severe underestimation of the asymmetry, around $1/2$ and $1/50$ of the true value for right-handed and left-handed top couplings to the octet, respectively. Interference effects are closely related to a $\mathcal{O}(1)$ transverse top polarisation, as yet not considered in this context.