Coherent Contributions to Isospin Mixing in the Mirror Pair As-67 and Se-67

Isospin symmetry breaking has been investigated in mass A=67 mirror nuclei through the experimental determination of the E1 strengths of analog electromagnetic transitions. Lifetimes of excited states have been measured in 67Se and 67As with the centroid shift method. Through the comparison of the B(E1) strengths of the mirror 9/2+→7/2- transitions, the isovector and the isoscalar components of the electromagnetic transition amplitude were extracted. The presence of a large isoscalar component provides evidence for coherent contributions to isospin mixing, probably involving the isovector giant monopole resonance.