Photoproduction of heavy vector mesons at HERA -a test field for diffraction

摘要

Exclusive diffractive photoproduction of heavy vector mesons (V = #PHI#, J/#psi#, and #gamma#) at HERA is studied in a model employing a dipole Pomeron exchange (P) with an inelastic #gamma#PV vertex. The model is fitted to the data on d#sigma#/dt, B, and #sigma#_(el) for Q~2 = 0 and beyond the threshold region. The elastic cross sections for both #PHI# and J/#psi# photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (indicating little or no shrinkage) for J/#psi# is not correlated with the slope of the Pomeron trajectory. Estimates for #gamma# photoproduction at HERA are given.