Excitation and decay of giant resonances in theCa40(e,e’x) reaction

Abstract

The Ca(e, e'x) reaction has been investigated for excitation energies between 8 and 26 MeV and momentum transfers from 0.25 to 0.66 fm ' at the continuous-wave electron accelerators MAMI at Mainz and S-DALINAC at Darmstadt. A multipole decomposition of the cross sections reveals strongly fragmented E2 (plus EO) strength around 14 and 17 MeV in contrast to all theoretical predictions. An-

Collective response of nuclei: Comparison between experiments and extended mean-field calculations

“…As in the case of 40 Ca, global shape of the strength exhibits a splitting of the GQR response into two main peaks at 10.8 MeV and 13.8 MeV.…”

“…This introduces a shift toward lower energy of the low energy part of the strength while the high energy part is pushed towards higher energies. In some cases, we may even expect that a single resonance is splitted into two peaks, as it happens for the GQR in 40 Ca.…”

“…The GQR response in 40 Ca is known to be split into two components with energy around 13.5 and 18 MeV with almost an equal fraction of the EWSR (around 30 % to 40 % for both peaks). The description of this fragmentation by microscopic calculations is a problem.…”

“…Such a behavior can be understood by looking at selfenergies themselves. An example, in figure 7, the coherent (thin lines) and the incoherent (thick lines) self-energies are shown for the GQR in 40 Ca. We see that the energy dependence of the real part of the self-energy is different in two different mechanisms.…”

“…In this work, we carry out investigations of nuclear collective response on the basis of a one-body stochastic transport theory, which incorporates both the coherent mechanism and the collisional damping in an consistent manner as demonstrated in [23,24] (also see [25,26]). We calculate the giant monopole, dipole and quadrupole responses in 40 Ca, 90 Zr, 120 Sn and 208 Pb , and compare the results with experiment in terms of Energy-Weighted Sum-Rules distribution. We find that both mechanisms play important role for a proper description of the fragmentation and the damping of giant resonance excitations.…”