The heavy quark parton oxymoron: A mini-review of heavy quark production theory in PQCD

Conventional perturbative QCD calculations on the production of a heavy quark 'H' consist of two contrasting approaches: the usual QCD parton formalism uses the zero-mass approximation (mH=0) once above threshold, and treats H just like the other light partons; on the other hand, most recent 'NLO' heavy quark calculations treat mH as a large parameter and always consider H as a heavy particle, never as a parton, irrespective of the energy scale of the physical process. By their very nature, both these approaches are limited in their regions of applicability. This dichotomy can be resolved in a unified general-mass variable-flavor-number scheme, which retains the mH dependence at all energies, and which naturally reduces to the two conventional approaches in their respective region of validity. Recent applications to lepto- and hadro-production of heavy quarks are briefly summarized