An improved description of charm fragmentation data

We consider the fragmentation of heavy quarks into heavy-flavoured hadrons, specifically the production of charmed mesons in e+e− collisions, at different centreof-mass energies. We focus our attention on the ratio of moments of the D∗+ energy spectrum measured by ALEPH and CLEO. This ratio is believed to provide us with a direct test of perturbative QCD evolution because hadronisation effects should cancel between the numerator and denominator. However, state-of the-art calculations based on standard (final-state) collinear factorisation fail to describe the experimental data. We show that this discrepancy is considerably reduced if heavy-quark threshold effects are accounted for not only in DGLAP evolution, as it is usually done, but also in the resummed coefficient functions