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

                                ZEUS Collaboration

                                   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, the ratio of E+p_parallel for the 
D* meson and that for the associated jet, where E is the energy and p_parallel 
the longitudinal momentum relative to the jet axis. Jets were reconstructed 
using the k_T clustering algorithm and required to have transverse energy
greater than 9 GeV. The D* meson associated with the jet was required to have 
a transverse momentum greater than 2 GeV. The measured function is compared to 
different fragmentation models incorporated in leading-logarithm Monte Carlo 
simulations and a next-to-leading-order calculation. The results are similar 
to those from e+e- experiments.