Improved formulation of global QCD analysis with zero-mass hard cross sections

The zero-mass (ZM) parton formalism is widely used in high-energy physics because of its simplicity and historical importance, even while massive quarks (c, b, t) are playing an increasingly prominent role in particle phenomenology, including global QCD analyses of parton distributions based on the more precise general-mass (GM) QCD formalism. In view of this dichotomy, we show how the obvious inconsistencies of the conventional implementation of the ZM formalism can be corrected, while preserving the simplicity of its hard matrix elements. The resulting intermediate-mass (IM) scheme for perturbative QCD calculation can be considered either as improved ZM formulation with realistic treatment of heavy-flavor kinematics; or as a simplified GM formulation with approximate ZM hard cross sections. Phenomenologically, global analyses based on IM calculations can effectively reproduce, within the present estimated uncertainty bands, the more correct GM results on parton distributions, as well as their predictions for a wide range of collider processes of current interest.