Measurement of the charm fragmentation function in D* photoproduction at HERA

TL;DR

This paper measures the charm fragmentation function in D* photoproduction at HERA, comparing experimental data with various theoretical models and previous e+e- results to improve understanding of charm quark hadronization.

Contribution

It provides the first detailed measurement of the charm fragmentation function in photoproduction at HERA and fits model parameters to data, enhancing fragmentation model accuracy.

Findings

Measured fragmentation function versus z variable.

Fitted model parameters to experimental data.

Compared results with e+e- experiment measurements.

Abstract

The charm fragmentation function has been measured in D* photoproduction with the ZEUS detector at HERA using an integrated luminosity of 120 pb-1. The fragmentation function is measured versus z = (E+p_parallel){D*}/2E{jet}, where E is the energy of the D* meson and p_parallel is the longitudinal momentum of the D* meson relative to the axis of the associated jet of energy E{jet}. Jets were reconstructed using the kT clustering algorithm and required to have transverse energy larger than 9 GeV. The D* meson associated with the jet was required to have a transverse momentum larger than 2 GeV. The measured function is compared to different fragmentation models incorporated in leading-logarithm Monte Carlo simulations and in a next-to-leading-order QCD calculation. The free parameters in each fragmentation model are fitted to the data. The extracted parameters and the function itself are compared to measurements from e+e- experiments.