Hadronic production of charm via flavour excitation

Abstract

We present a calculation of the contribution of flavour excitation diagrams to the hadronic production of open charm. The main new ingredients in the calculation are: (i) a proper treatment of the QCD evolution of the input charm sea distribution, with constraints from the existing charm structure function data; (ii) use of the available charm transverse momentum data to fix the t ̂ min cutoff which regulates the t ̂ ⋍ 0 divergence in the diagrams. We are then able to make a stable calculation of the resulting charm cross section. The flavour excitation contribution turns out to be an order of magnitude larger than for fusion. As a result the observed magnitudes of the charm cross section at accelerator and ISR energies are satisfactorily reproduced, thus eliminating a long standing difficulty of the perturbative QCD approach to open charm production. Furthermore, we calculate the longitudinal and transverse spectra of charmed hadrons using a simple recombination model. We show that the existing ISR data on the production of fast Λ c are well, and naturally, reproduced by this approach. Qualitative predictions for bottom production are also discussed.