The $B(E2)$ anomaly: Evidence for a low-lying mixed-symmetry collective excitation mode

Bo Cederwall, Chong Qi

Exceptionally low values of the ratio of electric quadrupole transition rates, $B_{4/2}\equiv B(E2;4_1^{+}\to 2_1^{+})/B(E2;2_1^{+}\to 0_{\mathrm{gs}}^{+})<1$, have been obse…