Open-charm hadroproduction and perturbative quantum chromodynamics

We critically study the method and the validity of perturbative QCD in open-charm hadroproduction. We explain how the gluon-fusion process ($G+G\to c+\overline{c}$) and the flavor-excitation process ($q+c\to q+c$ or $G+c\to G+c$) should be calculated in line with a principle of perturbative QCD (absorption of mass singularities into parton distributions), and without causing double counting. In this framework it is rather unlikely that the cross section of the excitation process is as large as ∼ 1 mb at CERN ISR energy $\sqrt{s}\simeq 60$ GeV. We discuss how large the cross section can be through possible higher-order effects. The $x_F$ distribution of charmed hadrons is also analyzed. By using a simple model for the recombination of charm quarks with fast-moving valence quarks, we show that it is easy to explain the observed hard spectrum of charm baryons.