Onset of triaxial deformation in Zn 66 and properties of its first excited 0+ state studied by means of Coulomb excitation

The electromagnetic structure of Zn66 at low excitation energy was investigated via low-energy Coulomb excitation at INFN Legnaro National Laboratories, using the Gamma Array of Legnaro Infn Laboratories for nuclEar spectrOscopy (GALILEO) γ-ray spectrometer coupled to the SPIDER (Silicon PIe DEtectoR). A set of reduced E2, E3, and M1 matrix elements was extracted from the collected data using the gosia code, yielding 12 reduced transition probabilities between the low-spin states and the spectroscopic quadrupole moment of the 21+ state. The B(E2) values for transitions depopulating the 02+ state have been determined for the first time, allowing for the lifetime of this state to be deduced and, consequently, the ρ2(E0;02+→01+) monopole transition strength to be extracted. In addition, the B(E3;31-→01+) value has been determined for the first time in a Coulomb excitation experiment. The obtained results resolve the existing discrepancies between literature lifetimes and demonstrate that Zn66 cannot be described by using simple collective models. Therefore, new state-of-the-art beyond-mean-field and large-scale shell-model calculations were performed in order to interpret the structure of this nucleus. Both the experimental and theoretical results suggest that the triaxial degree of freedom has an important impact on electromagnetic properties of Zn66, while the unique features of the 02+ state indicate its distinct and rather isolated structure.