Two-parton contribution to the heavy-quark forward-backward asymmetry in NNLO QCD

Forward-backward asymmetries, A(FB)(Q), are important observables for the determination of the neutral-current couplings of heavy quarks in inclusive heavy quark production, e(+)e(-) -> gamma*, Z* -> Q + X. In view of the measurement perspectives on A(FB)(Q) at a future linear collider, precise predictions of A(FB)(Q) are required for massive quarks. We compute the contribution of the Q (Q) over bar final state to A(FB)(Q) to order alpha(2)(s) in the QCD coupling. We provide general formulae, and we show that this contribution to A(FB)(Q) is infrared-finite. We evaluate these two-parton contributions for b and c quarks on and near the Z resonance, and for t quarks above threshold. Moreover, near the t (t) over bar threshold we obtain, by expanding in the heavy-quark velocity beta, an expression for A(FB)(t (t) over bar) to order alpha(2)(s) and NNLL in beta. This quantity is equal, to this order in beta, to the complete forward-back ward asymmetry A(FB)(t). (c) 2006 Elsevier B.V. All rights reserved.