CGS17

How the collective features emerge from the microscopic degrees of freedom is one of the main research themes in quantum many-body systems. Using the microscopic approach of the triaxial projected shell model (TPSM), the authors demonstrate that  admixing few quasiparticle excitations into the vacuum configuration with a fixed triaxiality parameter $\gamma$ provides a quantitative description of the shape fluctuations of the $\gamma$-soft nuclei.
 This is demonstrated by a detailed study of $^{104}$Ru, which reproduces a large set of experimental energies and $BE2$ matrix elements measured by COULEX [1]. 
The collective features are elucidated using the quadrupole shape invariant analysis, and also the staggering phase classification of the $\gamma$-band. A systematic study of twenty-two nuclei has been
carried out by means of the TPSM. The experimental energies of the yrast bands and $\gamma$ bands as well as the pertaining experimental $B(E2)$ values for intra and inter band transitions are very well reproduced. The signatures of triaxiality softness, as the position of the $2^+_2$ state relative to the $4^+_1$ state, the energy staggering of the $\gamma$ band, the position of the $0^+_2$ state and its
E2 decay are discussed.
[1] N. Nazir et al. Phys. Rev. C 107, L021303 (2023)