Influence of damping on the excitation of the double giant resonance

We study the effect of the spreading widths on the excitation probabilities of the double giant dipole resonance. We solve the coupledchannels equations for the excitation of the giant dipole resonance and the double giant dipole resonance. Taking Pb + Pb collisions as example, we study the resulting effect on the excitation amplitudes, and cross sections as a function of the width of the states and of the bombarding energy. Double giant dipole resonances have been mainly studied in heavy ion Coulomb excitation experiments at high energies (for a recent review, see [1]). The feasibility of such experiments has been predicted in 1986 [2, 3] where the magnitude of the cross sections for the excitation of the Double Giant Dipole Resonance (DGDR) was calculated (see also [4]). In ref. [3] a recipe was given for treating the effect of the width of the giant resonances on the excitation probabilities and cross sections. In this letter we make a quantitative prediction of this effect using a realistic coupled-channels calculation for the excitation amplitudes. The coupling interaction for the nuclear excitation i −→ f in a semiclassical calculation for a electric (π = E), or magnetic (π = M), multipolarity, is given by (eqs. (6-7) of ref. [5]) e-mail: [email protected] e-mails: [email protected] and [email protected]