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

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 Se-67 and As-67 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.