Superdeformed band in the $N = Z+4$ nucleus $^{40}$Ar: A projected shell model analysis

TL;DR

This study uses projected shell model calculations to analyze the superdeformed band in $^{40}$Ar, revealing a predominantly axially symmetric shape with collective rotational behavior and mixed quasiparticle configurations at high spins.

Contribution

It provides a detailed theoretical analysis of the superdeformed band in $^{40}$Ar, clarifying its shape and quasiparticle structure using angular-momentum-projection methods.

Findings

Energy levels indicate a perfect collective-rotor behavior.

Wave functions show dominance of mixed 0-, 2-, and 4-quasiparticle configurations.

Electric quadrupole transition probabilities match experimental data.

Abstract

It has been debated whether the experimentally-identified superdeformed rotational band in $^{40}$Ar [E. Ideguchi, et al., Phys. Lett. B 686 (2010) 18] has an axially or triaxially deformed shape. Projected shell model calculations with angular-momentum-projection using an axially-deformed basis are performed up to high spins. Our calculated energy levels indicate a perfect collective-rotor behavior for the superdeformed yrast band. However, detailed analysis of the wave functions reveals that the high-spin structure is dominated by mixed 0-, 2-, and 4-quasiparticle configurations. The calculated electric quadrupole transition probabilities reproduce well the known experimental data and suggest a reduced, but still significant, collectivity in the high spin region. The deduced triaxial deformation parameters are small throughout the entire band, suggesting that triaxiality is not very important for this superdeformed band.