Polarization transfer in the 16O(p,p') reaction at forward angles and structure of the spin-dipole resonances

In the present 16O(p,p') experiment, spin-flip and non-spin-flip transitions were separated by measuring the polarization transfer (PT) observables. Strong peaks due to M1 transitions were observed at Ex=16.22, 17.14 and 18.77 MeV. The 14.0 MeV-state, which was previously suggested to be excited by an M1 transition, is found to have a non-spin-flip nature. Non-spin-flip transitions with forward peaked cross sections were observed at excitation energies between 20 MeV and 27 MeV. These transitions are well reproduced by a calculation in which the excitation strengths are converted from the photoabsorption cross sections with normalization factor of 1.3. Therefore, it is concluded that the major part of the IVGDR strength is exhausted in the resonance region of Ex=20-27 MeV. Spin-flip strengths observed in the same energy region with the IVGDR are found to be excited with ΔL=1 angular momentum transfer. The resonances observed at Ex=20.9, 22.1 and 24.0 MeV carry both IVGDR and SDR(1-) strengths. The resonances at Ex=19.0 and 20.4 MeV are observed only in the spin-flip spectra and are, therefore, assigned to be 2- states. It was observed that the major part of the SDR(2-) strength in 16O is located at excitation energies below the SDR(1-). This result is consistent with the expectation that the three spin components of the SDR split in excitation energy in order of Ex(2-)<Ex(1-)<Ex(0-). (S.Y.)