Search for the GDR built on superdeformed nuclei

An experiment aiming at finding evidence for gamma-decay of the giant dipole resonance built on superdeformed nuclear states has been made using the EUROBALL gamma-detector array coupled to the large BaF2 detectors of the HECTOR system. The reaction Pd-110(Cl-37, 4n)Eu-143 at beam energies of 165 MeV and 170 MeV has been employed. A report of the analysis of a part of the data at E-beam = 165 MeV is given here. Results based on more inclusive and on very exclusive high-energy gamma-ray spectra am presented. In particular, the spectrum of high-energy gamma-rays gated by low-energy transitions between states fed by the superdeformed states are found to show some excess of yield in the 9-11 MeV region with respect to the spectrum gated by transitions not fed by the superdeformed states. This is the gamma-ray energy region where one expects to find the gamma-decay of the giant dipole oscillation along the long axis of a superdeformed axially symmetric nucleus. The measured excess is found to be of the same order as that predicted by schematic statistical model calculations assuming that the excitation of the GDR built on excited states is restricted to a region of the phase space a few MeV above the yrast line at very high spins.