Tevatron Top $A_{FB}$ Versus LHC Top Physics

TL;DR

This paper analyzes models explaining the Tevatron top A_{FB} anomaly in light of new LHC data, finding that many models are increasingly constrained or ruled out by current LHC measurements.

Contribution

It provides a comprehensive comparison of scalar and vector models for top A_{FB}, highlighting which are compatible with both Tevatron and LHC data.

Findings

Scalar models struggle to produce sufficient asymmetry.

Vector models can generate large asymmetry with less tension.

LHC data strongly constrains light and heavy mediators.

Abstract

We carry out a comprehensive analysis of models for top A_{FB} at CDF in light of new top data arriving from the LHC. We begin with a careful Tevatron analysis, considering in general which sets of effective vertices give rise to a large forward-backward asymmetry while suppressing the contribution to the total t tbar cross-section. We show on general grounds that scalar models struggle to produce sufficient asymmetries consistent with CDF observations, while vector models can produce a large asymmetry with a less significant tension in the total cross-section and $t\bar{t}$ invariant mass distribution at the Tevatron. We examine the essential observables of these models for top physics at LHC7 with 1 fb^{-1} of data, including the total cross-section, invariant mass distribution and number of additional jets in t tbar events. In the case of t-channel mediators, the LHC total cross-section places a strong constraint on light mediators, while the Tevatron invariant mass distributions place strong constraints on heavy mediators that are able to produce the asymmetry. Heavy axigluons are becoming increasingly squeezed by LHC7 t tbar and dijet resonance searches. We conclude that LHC7 top analyses are rapidly closing the window for viable models of the CDF top A_{FB}.