Diffractive Vector Meson Production at HERA
  The H1 and ZEUS collaborations at HERA report new data on the diffractive production of vector mesons with a many-fold increase of luminosity compared to previous measurements. The new data include photoproduction and electroproduction of $\rho^0,\phi,J/\psi$. The available data on elastic VM production indicate that the interaction scales as $Q^2+M_{V}^2$. 
B. Mellado