Excitation of open charm and factorization breaking in rapidity gap events at HERA

We develop the pQCD description of diffraction excitation of heavy flavours in DIS and we derive the analytic formulas for the mass spectrum in leading log mf2. The result illustrates nicely the non-factorization properties of the QCD pomeron. We predict a very steep rise of the charm content of diffraction dissociation of photons at small xP. We evaluate the contribution of open charm to scaling violations in the structure function of the pomeron.