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

Abstract

40Ar is among the few sd -shell nuclei known to exhibit superdeformation. An interesting question is whether the experimentally identified superdeformed rotational band in 40Ar has an axially or triaxially deformed shape. Projected shell model calculations assuming an axially deformed basis are performed up to high spins for this nucleus. Our detailed analysis of the wave functions reveals that the high-spin states are dominated by mixed 0-, 2-, and 4-quasiparticle configurations with different K-components. 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. Due to the mixing of various multi-quasiparticle K-configurations, axial asymmetry emerges in the calculation. Throughout the entire rotational band, the extracted triaxial deformation parameters are small but non-zero. Relations of triaxiality and unnatural spin-parity states of the superdeformed side-band are discussed.