Interpretations and implications of the top quark rapidity asymmetriesAFBtandAFBℓ

Abstract

Forward-backward asymmetries ${A}_{\mathrm{FB}}^{t}$ and ${A}_{\mathrm{FB}}^{\ensuremath{\ell}}$ are observed in the top-quark $t$ rapidity distribution and in the rapidity distribution of charged leptons $\ensuremath{\ell}$ from top-quark decay at the Tevatron proton-antiproton collider, and a charge asymmetry ${A}_{\mathrm{C}}$ is seen in proton-proton collisions at the Large Hadron Collider (LHC). In this paper, we update our previous studies of the Tevatron asymmetries using the most recent data. We provide expectations for ${A}_{\mathrm{C}}$ at the LHC based first on simple extrapolations from the Tevatron, and second based on new physics models that can explain the Tevatron asymmetries. We examine the relationship of the two asymmetries ${A}_{\mathrm{FB}}^{t}$ and ${A}_{\mathrm{FB}}^{\ensuremath{\ell}}$. We show their connection through the ($V\ensuremath{-}A$) spin correlation between the charged lepton and the top quark with different polarization states. We show that the ratio of the two asymmetries provides independent insight into the physics interpretation of the top-quark asymmetry. We emphasize the value of the measurement of both asymmetries, and we conclude that a model which produces more right-handed than left-handed top quarks is suggested by the present Tevatron data.