Transverse Top Quark Polarization and the ttbar Forward-Backward Asymmetry

TL;DR

This paper proposes that broad top-antitop resonances can induce measurable transverse polarization of top quarks, providing a new observable to detect new physics related to the Tevatron's forward-backward asymmetry anomaly.

Contribution

It introduces the idea that broad ttbar resonances cause transverse top polarization, which can serve as a novel signature of new physics beyond the Standard Model.

Findings

Broad ttbar resonances induce net transverse top polarization.

The polarization is consistent with spacetime symmetries and absent in leading-order QCD.

The induced polarization could be observable at Tevatron or LHC.

Abstract

The forward-backward asymmetry in top pair production at the Tevatron has long been in tension with the Standard Model prediction. One of the only viable new physics scenarios capable of explaining this anomaly is an s-channel axigluon-like resonance, with the quantum numbers of the gluon but with significant axial couplings to quarks. While such a resonance can lead to a clear bump or excess in the ttbar or dijet mass spectra, it may also simply be too broad to cleanly observe. Here, we point out that broad ttbar resonances generally lead to net top and antitop polarizations transverse to the production plane. This polarization is consistent with all discrete spacetime symmetries, and, analogous to the forward-backward asymmetry itself, is absent in QCD at leading order. Within the parameter space consistent with the asymmetry measurements, the induced polarization can be sizable, and might be observable at the Tevatron or the LHC.