Low-lying structure and shape evolution in neutron-rich Se isotopes

Neutron-rich $^{88,90,92,94}$ Se isotopes were studied via in-beam $\gamma$-ray spectroscopy after nucleon removal reactions at intermediate energies at the Radioactive Isotope Beam Factory. Based on gamma-gamma coincidence analysis, low-lying excitation level schemes are proposed for these nuclei, including the 2$_1^+$, 4$_1^+$ states and 2$_2^+$ states at remarkably low energies. The low-lying 2$_2^+$ states, along with other features, indicate triaxiality in these nuclei. The experimental results are in good overall agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, which suggests both triaxial degree of freedom and shape coexistence playing important roles in the description of intrinsic deformations in neutron-rich Se isotopes.