Leading Particle Effect in the $J\mathrm{/}\mathrm{\Psi }$ Elasticity Distribution

Recent DESY-HERA data on $J\mathrm{/}\mathrm{\Psi }$ elasticity distribution show that it emerges mostly as a fast particle. Interpreting photoproduction as a collision between a pre-formed charmed hadron and the proton, the outcoming $J\mathrm{/}\mathrm{\Psi }$ is a leading particle of the collision. We analyse these data using a model formulated to describe energy flow in hadron-hadron reactions. The measured $J\mathrm{/}\mathrm{\Psi }$ spectrum can be successfully described in terms of this model. We conclude that the observed transparency of the charmed hadron-proton collisions arises because of the particularly small gluonic content of the initial $c - \bar c$ state.