Diffraction at HERA
  Precision measurements of diffraction have been performed by the H1 and ZEUS experiments at the HERA collider with high statistics for a wide kinematic range of photon virtuality $Q^2$. The diffractive parton densities are extracted by performing the NLO DGLAP QCD fits to diffractive data and can be used to test QCD factorisation with diffractive final states. 
Heuijin Lim