B(E2) anomaly and triaxial deformation in the interacting boson model

TL;DR

This paper investigates how triaxial deformation influences the anomalous B(E2) transition rates in the interacting boson model, explaining experimental data and revealing the universality of the anomaly across different triaxial schemes.

Contribution

It introduces a comprehensive analysis of triaxial effects on B(E2) anomalies in IBM, demonstrating the phenomenon's occurrence in all triaxial schemes and providing a theoretical explanation for experimental observations.

Findings

B(E2) anomaly occurs in all triaxial schemes due to band-mixing.

The model explains depressed B_{4/2} values in certain nuclei.

Triaxial dynamics are crucial for understanding E2 transition behaviors.

Abstract

The influences of triaxial dynamics on the anomalous $E2$ transitional behaviors in the interacting boson model (IBM) have been comprehensively examined without symmetry restrictions. Specifically, different triaxial schemes in the IBM have been analyzed using a general procedure for deriving triaxial rotor modes based on two distinct approaches. The results indicate that the $B(E2)$ anomaly feature, characterized by $B_{4/2}=B(E2;4_1^+\rightarrow2_1^+)/B(E2;2_1^+\rightarrow0_1^+)<1.0$, can occur in all triaxial schemes due to strong band-mixing effects. This finding is further tested in describing the available data for $^{172}$Pt,~$^{168,170}$Os and $^{166}$W using the model constructed upon the extended consistent-$Q$ formula, providing a simple theoretical explanation of the depressed $B_{4/2}$ values observed in the experiments.