Triaxiality in the interacting boson model

The signature splitting of the γ-vibrational band of several Ru, Pd, Xe, Ba, Os and Pt isotopes is analyzed in the framework of the interacting boson model (IBM). The nuclei studied are close to the γ-unstable SO(6) limit of the IBM and have well-known γ bands. It is shown that in most nuclei the signature splitting is better reproduced by the inclusion of a three-body interaction between the d bosons. In none of the nuclei evidence for a stable, triaxial ground-state shape is found.