Isospin Symmetry violation in mirror E1 transitions: Coherent contributions from the Giant Isovector Monopole Resonance in 67As - 67Se

TL;DR

This paper investigates the violation of isospin symmetry in mirror E1 transitions, proposing that Coulomb-induced mixing with the Giant Isovector Monopole Resonance explains the observed asymmetry in 67As - 67Se.

Contribution

It introduces the idea that the Giant Isovector Monopole Resonance causes significant asymmetry in mirror E1 transitions due to Coulomb effects.

Findings

Large asymmetry observed in 67As - 67Se E1 transitions.

Coulomb-induced mixing with the Giant Isovector Monopole Resonance explains the asymmetry.

Minimal impact on other nuclear properties.

Abstract

The assumption of an exact isospin symmetry would imply equal strengths for mirror E1 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 67As - 67Se 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 E1 transitions, with comparatively small effect on the other properties of the parent and daughter levels.