Photoproduction of Vector Mesons at Large Transfer
  At forward angles, the cross-sections of photoproduction of vector mesons ($\rho$, $\omega$, and $\phi$) are well accounted for by the exchange of the Pomeron at high energies, while contributions of $t$ channel exchange of Reggeons are significant at low energies. At large angles, the impact parameter becomes small enough to prevent their constituents to build up the exchanged Reggeons or Pomeron. Two gluon exchange appears to dominate above $-t\simeq 1$ GeV$^2$, especially in the $\phi$ channel. 
J.M. Laget