J/psi production via fragmentation at HERA

We compute the contributions to large-$p_T$ $J/\psi$ production at HERA coming from fragmentation of gluons and charm quarks. We find that the charm quark fragmentation contribution dominates over the direct production of $J/\psi$ via photon-gluon fusion at large-$p_T$, while the gluon fragmentation is negligibly small over the whole range of $p_T$. An experimental study of $p_T$ distributions of $J/\psi$ at HERA will provide a direct probe of the charm quark fragmentation functions