Delta Delta excitation in proton-proton induced [pi] super(0)[pi] super(0) production

Exclusive measurements of the pp-->pp[pi] super(0)[pi] super(0) reaction have been performed at CELSIUS/WASA at energies from threshold up to T sub()p1.3 GeV. Total and differential cross sections have been obtained. Here we concentrate on energies T sub()pinline image]1 GeV, where the Delta Delta excitation becomes the leading process. No evidence is found for a significant ABC effect beyond that given by the conventional t-channel Delta Delta excitation. This holds also for the double-pionic fusion to the quasibound super(2)He. The data are compared to model predictions, which are based on both [pi]- and [rho]-exchange. Total and differential cross sections are at variance with these predictions and call for a profound modification of the [rho]-exchange. A phenomenological modification allowing only a small [rho]-exchange contribution leads to a quantitative description of the data.