Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at E_p = 200 MeV. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon-nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle two-hole (2p-2h) states.Comment: Phys. Lett. B, in pres

Excitation and decay of giant-resonances in the CA-40(E,E'X) reaction

The Ca-40(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-1 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 E0) strength around 14 and 17 MeV in contrast to all theoretical predictions. Angular correlations of proton decay are described over the entire energy range by a continuum random-phase-approximation approach. A comparison of the branching ratios to statistical model calculations provides information on the dominant damping mechanism

Role of knockout contributions in giant resonance studies with (p ,p′ x) reactions

The giant-resonance region in 40Ca and 48Ca has been studied using the reactions 48Ca(p ,p′ n0)47Ca, 40Ca(p ,p′ p0)39K, and 40Ca(p ,p′ α0)36Ar for an incident proton energy Ep= 100 MeV. Knockout cross sections for these reactions were calculated within the distorted wave impulse approximation formalism using parameters fixed from previous investigations. The results quantitatively account for the data at higher excitation energies while the knockout contributions underneath the main resonance strength are small.Articl