Incident-energy dependence of the analyzing power in the ⁵⁸Ni(p,³He)⁵⁶Co reaction between 80 and 120 MeV

We investigate the possible incident energy dependence of the analyzing power in the reaction ⁵⁸Ni(p,³He)⁵⁶Co. Previous inclusive (p,³He) reaction studies, described in terms of a statistical multistep formalism, have indicated a slight decrease in analyzing power at the very low excitation energies. This seems to contradict the understanding that the low excitation energy region is dominated by a direct reaction mechanism with large analyzing power values. To better understand this discrepancy, the excitation to low lying states in the residual nucleus has recently been investigated by means of a high resolution spectrometer at incident energies between 80 and 120 MeV. We present the experimental differential cross section and analyzing power angular distribution data for the three incident energies, compared with macroscopic Distorted-Wave Born Approximation (DWBA) calculations for a few discrete states of ⁵⁶Co, assuming a single-step deuteron pickup mechanism. The success of the DWBA calculations in tracing the data over the range of incident energies, provides confidence in the use of this simple direct pickup description in the multistep formalism. It seems also plausible that the analyzing powers of the prominent L-transfers can combine in such a way as to produce the observed quenching in the analyzing powers. (author)