Combined analysis of charm-quark fragmentation-fraction measurements

TL;DR

The paper tests the universality of charm-quark fragmentation fractions by combining measurements from e+e−, e±p, and pp collisions, updating inputs with current branching ratios and treating correlated uncertainties. A MINUIT-based χ^2 minimisation with a normalisation constraint S extracts f(c→H) for multiple hadrons, yielding a globally consistent set with substantially reduced uncertainties. The analysis finds general agreement across production environments, though the LEP-derived sum S_Z shows a modest deviation from unity. An extension to excited charm states provides additional fragmentation fractions, and the overall results support a largely production-process-independent fragmentation mechanism with improved precision for practical phenomenology in QCD predictions.

Abstract

A summary of measurements of the fragmentation of charm quarks into a specific hadron is given. Measurements performed in photoproduction and deep inelastic scattering in $e^{\pm}p$, $pp$ and $e^+e^-$ collisions are compared, using up-to-date branching ratios. Within uncertainties, all measurements agree, supporting the hypothesis that fragmentation is independent of the specific production process. Averages of the fragmentation fractions over all measurements are presented. The average has significantly reduced uncertainties compared to individual measurements.

Figures (2)

• Figure 1: The values of charm-quark fragmentation fractions, $f(c\rightarrow H)$, in different experiments with the $S$ constraint. The global combination with the $S$ constraint is shown with the shaded band. Averages of included data in different production regimes are shown with various full symbols.
• Figure 2: The values of $R_{u/d}$, $P^d_V$ and $\gamma_s$ in different experiments with the $S$ constraint. The global combination with the S constraint is shown with the shaded band. Combinations of included data in different production regimes are shown with various full symbols. Data that were not included in the combination Acosta:2003axDavid:2007iv are shown with open symbols. Note, that the latter are quoted from the original papers, i.e. without correction to the up-to-date branching ratios and with no branching ratio uncertainty, if not given in the source.