Production of vector mesons and measurement of the hadronic component of   photon light-cone wave function at HERA
  A detailed study of vector meson production ($\phi$ and $J/\psi$) in $e^\pm p$ collisions at HERA with the ZEUS and H1 detector has been performed. The cross sections are measured as a function of $Q^2$, $W$ and $t$. In this contribution, the results are summarised, compared to theoretical calculations and the dynamical picture emerging in perturbative QCD is highlighted. The measurement of the hadronic component of the photon light-cone wave function in the exclusive production of di-pions, $ep\to e \pi^+\pi^- p$ is also reported. 
N. Coppola, (on behalf of the H1 and ZEUS Collaborations)