Cross sections at HERA

The energy dependence of a given process teaches us about the dynamics of this process. If the energy dependence can be described by a Reggetype approach a la Donnachie and Landshoff [1] we call the process soft. The total hadron-proton cross sections dependence on center-of-mass energy exemplifies the behaviour of soft processes.. If the energy dependence can be described by perturbative QCD (pQCD) we say that the process is hard. An example is exclusive J/ψ electroproduction [2, 3]. The nice feature of ep interactions at HERA is that we can see the interplay between soft and hard interactions [4]. Jan Kwiecinski made very many and important contributions to this subject by studying actually all possible reactions, like hadron-hadron (hh), γp, γγ and ep. Many of the studies that we have been doing at HERA were inspired by his findings. In this sense it is very appropriate that this conference is dedicated to his memory. What sets the baseline for soft processes? Donnachie and Landshoff (DL) showed [1] that all hh total cross sections can be described by a simple expression containing two terms, inspired by Regge theory [5], one term representing the contribution of the effective Pomeron trajectory and a second term of a Regge trajectory,