An improved description of charm fragmentation data

TL;DR

This paper investigates charm quark fragmentation into D*+ mesons in electron-positron collisions, highlighting the importance of including threshold effects in both DGLAP evolution and coefficient functions to match experimental data.

Contribution

It introduces an improved theoretical description of charm fragmentation by incorporating heavy-quark threshold effects in both evolution and coefficient functions.

Findings

Discrepancy between data and standard calculations is reduced with threshold effects.

Including threshold effects in coefficient functions improves data description.

Enhanced theoretical model aligns better with experimental measurements.

Abstract

We consider the fragmentation of heavy quarks into heavy-flavoured hadrons, specifically the production of charmed mesons in $e^+e^-$ collisions, at different centre-of-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.