Energy and $Q^2$ dependence of elastic vectormeson production and the proton structure function $F_2$

Abstract

In the framework of the Model of the Stochastic Vacuum elastic hadron-hadron scattering, photo- and electroproduction of vectormesons and also F_2(Q^2) can be well described at center of mass energy approximately 20 GeV. The scattering amplitude is derived by smearing the color dipole-dipole scattering, which is calculated nonperturbatively in the Model of the Stochastic Vacuum, with appropriate wavefunctions. For the considered processes the dipoles have extensions in the range of hadron sizes. We now extend this idea to small dipoles and high energies. The energy dependence is modeled in a phenomenological way: we assume that there a two pomerons, the soft- and the hard-pomeron, each being a simple pole in the complex angular plane. We couple dipoles of hadronic size to the soft-pomeron and small dipoles to the hard-pomeron. For small dipoles we take the perturbative gluon exchange into account. By that way we obtain an energy dependent dipole-dipole scattering amplitude which can be used for all the processes with the same parameters. We show that this approach can describe in addition to all the low energy results (20 GeV) also the HERA data for the considered processes in a large energy and Q^2 range. Especially the right transition from the soft to the hard behavior is observed.