Some ingredients for a reliable extraction of spectroscopic factors from one-nucleon transfer reactions

The methodology employed for obtaining information on the microscopic, in the sense of the shell model, constituents of nuclear states has not changed appreciably since it was first introduced in the late 50´s. Nevertheless, the extremely simple interpretation, which considers the capture of one nucleon either from, or into, a defined shell model orbital by a bypassing loosely bound projectile has proven rather successful. The method allows to extract the corresponding orbital angular momentum and the spectroscopic factor, which indicates the fraction of the real state explained by the model. It is, further, usual to consider the distorted wave Born approximation (DWBA) in the description of the reaction, which means going in a single step from the initial to the final condition, where the respective interacting pairs are represented by the distorted waves at the corresponding energy, considering only the elastic scattering process in the optical model perspective. There are several possibilities of extracting inconsistent information from one-nucleon transfer reactions. Initially, caution should be applied if different descriptions of the well, to which the nucleon is bound, are employed. This results in different absolute values for the spectroscopic factors, but does not affect the pattern of the predicted angular distribution, and thus, the value obtained for the transferred orbital angular momentum. Although usually the relative values of the spectroscopic factors are not changed, sums of spectroscopic intensities, related to total occupancies or vacancies of the respective orbital, may be altered by significant amounts. Another source of troubles are ad-hoc changes in optical model parameters, specially if adjusted to a single elastic scattering angular distribution, corresponding to jus