Pygmy dipole response of proton rich argon beyond the random phase approximation

TL;DR

This paper investigates the pygmy dipole resonance in proton-rich argon isotopes Ar-32 and Ar-34 using advanced theoretical methods, comparing RPA and shell model predictions to understand the resonance's characteristics.

Contribution

It introduces a detailed comparison of RPA and shell model approaches for pygmy dipole resonances in proton-rich argon isotopes, highlighting the effects of configuration mixing.

Findings

A clear pygmy resonance peak in Ar-32.

Pygmy states in Ar-34 are close to and mix with the giant dipole resonance.

Configuration mixing broadens and reduces pygmy strength.

Abstract

The occurrence of a pygmy dipole resonance in proton rich Ar-32 and Ar-34 is studied using the unitary correlator operator method interaction Vucom, based on Argonne V18. Predictions from the random phase approximation (RPA) and the shell model in a no-core basis are compared. It is found that the inclusion of configuration mixing up to two-particle--two-holes broadens the pygmy strength slightly and reduces sensibly its strength, as compared to the RPA predictions. For Ar-32 a clear peak associated with a pygmy resonance is found. For Ar-34, the pygmy states are obtained close to the giant dipole resonance and mix with it.