arXiv subjects
Publications and source records attributed to Xavier Janssen.
Exclusive vector meson production and deeply virtual Compton scattering are ideally suited reactions for studying the structure of the proton and the transition from soft to hard processes. The main experimental data obtained at HERA are summarised and presented in the light of QCD approaches.
The electroproduction of rho mesons is studied at HERA with the H1 detector at high Q^2 and high |t|. Cross sections are measured as a function of Q^2, W and t. The W dependence of the gamma*-p cross section is observed to increase with Q^2 from values compatible with soft Pomeron exchange at low Q^2 to a hard dependence at large Q^2. Spin density matrix elements are measured and their dependence is compared with a two gluon exchange model.