Collider-independent t tbar forward-backward asymmetries

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(Submitted on 9 May 2012)

We introduce the forward-backward asymmetries A_u, A_d corresponding to u ubar, d dbar -> t tbar production, respectively, at hadron colliders. These are collider- and centre-of-mass-independent observables, directly related to the forward-backward and charge asymmetries measured at the Tevatron and the LHC, respectively. We discuss how to extract these asymmetries from data. Because these asymmetries are collider-independent, their measurement at these two colliders could elucidate the nature of the anomalous forward-backward asymmetry measured at the Tevatron.

QCD Coherence and the Top Quark Asymmetry

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Peter Z. Skands, Bryan R. Webber, Jan Winter

(Submitted on 7 May 2012)

Coherent QCD radiation in the hadroproduction of top quark pairs leads to a forward–backward asymmetry that grows more negative with increasing transverse momentum of the pair. This feature is present in Monte Carlo event generators with coherent parton showering, even though the production process is treated at leading order and has no intrinsic asymmetry before showering. In addition, depending on the treatment of recoils, showering can produce a positive contribution to the inclusive asymmetry. We explain the origin of these features, compare them in fixed-order calculations and the Herwig++, Pythia and Sherpa event generators, and discuss their implications.

arXiv:1205.1466v1 [hep-ph]