Isospin symmetry violation in mirror $E1$ transitions: Coherent contributions from the giant isovector monopole resonance in the ${}^{67}$As-${}^{67}$Se doublet

Isospin symmetry violation in mirror $E 1$ transitions: Coherent contributions from the giant isovector monopole resonance in the $^{67}$ As- $^{67}$ Se doublet

P. G. Bizzeti, G. de Angelis, S. M. Lenzi, and R. Orlandi

Phys. Rev. C 86, 044311 – Published 9 October 2012

Abstract

The assumption of an exact isospin symmetry would imply equal strengths for mirror $E 1$ transitions (at least, in the long-wavelength limit). Actually, large violations of this symmetry rule have been indicated by a number of experimental results, the last of which is the $^{67}$ As- $^{67}$ Se doublet investigated at GAMMASPHERE. Here, we examine in detail various possible origins of the observed asymmetry. The coherent effect of Coulomb-induced mixing with the high-lying giant isovector monopole resonance is proposed as the most probable process to produce a large asymmetry in the $E 1$ transitions, with comparatively small effect on the other properties of the parent and daughter levels.