Coherent contributions to isospin mixing in the mirror pair {sup 67}As and {sup 67}Se.

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 {sup 67}Se and {sup 67}As with the centroid shift method. Through the comparison of the B(E1) strengths of the mirror 9/2{sup +} {yields} 7/2{sup -} 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.