Ni58(p→,p′)reaction at 60 MeV: Study of the analyzing power for inelastic excitation of the giant resonance region of the nuclear continuum and of low-lying bound states

The analyzing power of the giant resonance region of the nuclear continuum and of low-lying bound states for incident 60-MeV polarized protons has been investigated in the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}(\overrightarrow{p},p^{\prime })$ reaction. The measurements are compared with collective-model distorted-wave Born-approximation calculations employing a spin-orbit transition potential of the full-Thomas form and optical-model parameters which give a good description of the analyzing power for proton elastic scattering from ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at 60 MeV. The predicted analyzing powers for the giant quadrupole ($E2\mathrm{}$) resonance at $E_x=16.5$ MeV and for low-lying bound states with $J^{\pi }=2^{+},3^{-},\mathrm{and}{4}^{+}$ are in qualitative agreement with the measurements for ${\theta }_{\mathrm{lab}}=15-60\mathrm{}°$. However, a systematic discrepancy is observed for the quadrupole resonance, where the measurements for ${\theta }_{\mathrm{lab}}=15-30°$ are considerably more negative than the calculations. A similar but less pronounced effect is observed for the strongly excited $2^{+}$ and $3^{-}$ bound states. Improved fits to the analyzing power for the quadrupole resonance are obtained by reducing the spin-orbit diffuseness parameter or by including an attractive imaginary spin-orbit potential. Analysis of the cross section for a weaker resonance at $E_x=13.5$ MeV indicates an $E2\mathrm{}$ assignment. The analyzing power for the unstructured nuclear continuum above the giant resonance region is $A_y\approx -0.05\mathrm{}\pm 0.01$ at most angles between 15 and 40°.