Elementary Interactions between hadrons
Concerning the interaction among hadrons it has turned out that various hadronic reaction channels cannot be treated separately from each other due to rescattering effects. The coupled-channel K-matrix approach including on equal footing the channels (pi, N), (gamma, N), (eta, N), (K,Lambda), (K,Sigma) and (2pi, N) has recently been extended to include also (omega, N) and the J = 5/2 nucleon resonances. In this way cross sections can be calculated up to an invariant mass of 2 GeV and the question which resonances couple to the (omega, N) channel could be tackled. This is e.g. interesting for in-medium calculations for vector mesons (see below). In general, the ingredients for the description of meson-nucleon and photon-nucleon interactions are coupling constants and resonance masses. If single reactions were treated separately from each other, one would have a lot of freedom for choosing the input parameters. Hence the predictive power of such an approach and the understanding of the relevant physics would be low. In contrast, our coupled-channel approach allows to highly constrain these input parameters as a lot of channels (i.e. data) have to be explained with the same parameter set. This opens the door for a deeper understanding of the reaction mechanisms and the properties of the relevant degrees of freedom.
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