Coherent Description of D^{*+-} Production in e^+e^- and Low-Q^2 ep Collisions
J. Binnewies, B. A. Kniehl, G. Kramer
TL;DR
This work derives universal $D^{*\pm}$ fragmentation functions (FFs) for charm and bottom by fitting LEP1 data within a massless-charm factorization framework, using two input forms (standard and Peterson) and performing NLO evolution. The resulting FFs describe lower-energy $e^+e^-$ data and $D^{*\pm}$ photoproduction at HERA, supporting fragmentation universality across processes and scales. The analysis quantifies branching fractions and mean momentum fractions, revealing how $\langle x\rangle_c(\mu)$ decreases with scale while the charm content of the photon remains the dominant source of uncertainty in photoproduction. These FFs provide a robust tool for predicting $D^{*\pm}$ production in high-energy experiments and offer a pathway to constrain the charm PDF of the photon with future precise measurements.
Abstract
We present new sets of fragmentation functions for D^{*+-} mesons, both at leading and next-to-leading order. They are determined by fitting LEP1 data on inclusive D^{*+-} production in e^+e^- annihilation. In one of the sets, we take the charm-quark fragmentation function to be of the form proposed by Peterson et al. and thus obtain updated values of the epsilon_c parameter and the c -> D^{*+} branching ratio. The new fragmentation functions lead to an excellent description of other e^+e^- data with centre-of-mass energies between 10 and 35 GeV. They also nicely agree with recent HERA data on inclusive D^{*+-} photoproduction in ep collisions, which may be considered as a test of the universality of the fragmentation into D^{*+-} mesons.