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

The charm fragmentation function was measured in D* photoproduction with 
the ZEUS detector at HERA using an integrated luminosity of 120 pb-1. The 
fragmentation function is presented versus z, the ratio of E + p_parallel 
of the D* meson and of 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 a 
transverse energy larger than 9 GeV. The D* meson associated with the jet 
was required to have a transverse momentum greater than 2 GeV. The 
measurement 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.