A recent proton scattering experiment performed with 500 MeV protons has demonstrated a systematic quenching of the isovector spin-dipole strength. This report describes two mechanisms which can each contribute to the quenching: the effect of 2p-2h ground-state correlations and the spreading width that arises from the coupling of 1p-1h to 2p-2h excitations. The contributions from both effects bring theory within the range of experimental observation and indicate that these effects should be included in future calculations in which the origin of inhibition of spin-dependent excitations needs to be understood.

• Received 24 July 1989

DOI:https://doi.org/10.1103/PhysRevC.41.786