Spin- and Parity-Resolved Level Densities from the Fine Structure of Giant Resonances

Abstract

Level densities of ${J}^{\ensuremath{\pi}}={2}^{+}$ and ${2}^{\ensuremath{-}}$ states extracted from high-resolution studies of $E2$ and $M2$ giant resonances in $^{58}\mathrm{Ni}$ and $^{90}\mathrm{Zr}$ are used to test recent predictions of a possible parity dependence. The experimental results are compared to a combinatorial approach based on the Hartree-Fock-Bogoliubov model and to shell-model Monte Carlo calculations including both spin and parity projection. No parity dependence is observed experimentally, which is in agreement for $^{90}\mathrm{Zr}$ but in contrast with the model predictions for $^{58}\mathrm{Ni}$.