Recent results on diffractive and forward physics at HERA

Abstract

Abstract.Recent studies on diffractive processes in ep scattering at HERA are reviewed. Heavy quark production in diffractive processes was studied by tagging a D * meson in diffractive DIS events. The cross section for events with a prompt photon in the final state was also measured. The data are well reproduced by models using diffractive parton densities determined from inclusive diffractive DIS cross sections. Two studies were also made on exclusive vector meson production. The cross-section ratio σ(ψ(2S ))/σ(ψ(1S )), which reflects the difference in transverse shape of the charmonium wave functions, are compared to various models. Moreover, the diffractive ρ 0 photoproduction with a forward neutron, which has two vertices with small-p T recoil, were measured to study factorisation properties. The data show some indication of re-scattering.