Tevatron Top Quark Forward-Backward Asymmetry -- Implications for Same-sign Top Quark Pair Production

Abstract

The forward-backward asymmetry for top quarks measured in proton-antiproton collisions at the Tevatron shows an interesting deviation from standard model expectations. Among possible interpretations, the exchange of a non-universal, flavor-changing $Z^\prime$ is of some interest as it naturally predicts a top quark in the forward region of rapidity. To reproduce the size of the Tevatron asymmetry, the couplings of the $Z^\prime$ to standard model quarks must be large, inevitably leading to production of same-sign top quark pairs at the Tevatron and at the Large Hadron Collider (LHC). We discuss the constraints on this model from (a) the Tevatron $t \bar{t}$ cross section, (b) the Tevatron $t \bar{t}$ invariant mass distribution, and the limits at the Tevatron on the same sign top quark pair cross section. We explore the discovery potential for $tt$ and $ttj$ production in early LHC experiments at 7 TeV and conclude that if a $tt$ signal is not observed with 1 fb$^{-1}$ of integrated luminosity, then a non-universal $Z^\prime$ alone cannot explain the Tevatron forward-backward asymmetry. Limits on the same sign cross section at the LHC from the CMS collaboration already disfavor this interpretation of the reported asymmetry.