Portrait of a colour octet

TL;DR

This paper investigates the potential of a light colour octet particle to explain anomalies in top quark pair production asymmetries, fitting model parameters to collider data and predicting related observables.

Contribution

It provides the first comprehensive fit of a light colour octet to combined Tevatron and LHC top quark data, highlighting the viability of right-handed couplings.

Findings

A right-handed colour octet fits all current data well.

Predictions made for top polarisation and unmeasured observables.

Constraints on octet couplings from collider measurements.

Abstract

New colour octets stand out among the new physics proposals to explain the anomalous forward-backward asymmetry measured in $t \bar t$ production by the CDF experiment at the Tevatron. We perform a fit to $t \bar t$ observables at the Tevatron and the LHC, including total cross sections, various asymmetries and the top polarisation and spin correlations, to find the most likely parameters of a light colour octet to be consistent with data. In particular, an octet coupling only to right-handed quarks gives a good fit to all measurements. The implications from the general fit are drawn in terms of predictions for top polarisation observables whose measurements are yet not very precise, and observables which simply have not been measured.