The forward-backward asymmetry at NNLO revisited

TL;DR

This work revisits the forward-backward asymmetry for flavoured quarks in e+e- annihilation and introduces an infrared-safe observable defined via flavoured quark jets using the flavour-k_perp algorithm. It computes the NLO and NNLO QCD corrections within a subtraction framework, leveraging a general NNLO program for e+e- → 2 jets, and carefully treats four-quark final states. The results show small NNLO corrections, especially under stringent two-jet cuts, indicating the observable can support high-precision measurements at future linear colliders. By resolving IR-safety issues, the approach provides a robust path to precise determinations of electroweak parameters from heavy-quark asymmetries.

Abstract

I reconsider the forward-backward asymmetry for flavoured quarks in electron-positron annihilation. I suggest an infrared-safe definition of this observable, such that the asymmetry may be computed in perturbative QCD with massless quarks. With this definition, the first and second order QCD corrections are computed.