Factorisation breaking in diffraction

The high energies of the HERA ep collider and of the Tevatron collider allow for the first time to study diffractive interactions in the presence of a hard scale and to describe them in terms of perturbative QCD. In QCD the diffractive exchange is described in terms of partons, and the factorisation theorem states that the cross section for hard interactions can be estimated as convolution of universal diffractive parton distribution functions and process-dependent coefficients, perturbatively calculable. Recent experimental data from the H1 and ZEUS Collaborations at HERA are presented for diffractive dijet and D∗ meson production, in both deep-inelastic scattering and photoproduction regime and compared to next-to-leading order QCD predictions using diffractive parton distributions. The validity of the QCD factorisation theorem is investigated.