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

TL;DR

This study investigates the fine structure of the isoscalar giant quadrupole resonance in 40Ca, revealing that Landau damping at the mean-field level explains the observed energy scales, contrasting with heavier nuclei.

Contribution

It demonstrates that Landau damping accounts for the fine structure in 40Ca's ISGQR, supported by wavelet analysis and RPA calculations, challenging previous explanations involving 2p-2h couplings.

Findings

Experimental energy scales match RPA and second-RPA predictions.

Fine structure originates from Landau damping at the mean-field level.

Contrasts with heavier nuclei where 2p-2h couplings dominate.

Abstract

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.