Microscopic Optical Potentials for Elastic Nucleon-Nucleus Scattering

The theoretical approach to the elastic scattering of a nucleon from a nucleus, pioneered by Watson [1], made familiar by Kerman, McManus, and Thaler (KMT) [2] and further developed as the spectator expansion [3, 4, 5, 6] is now being applied with striking success. In a similar vein, a slightly di erent approach to the multiple scattering expansion within the KMT framework is being pursued by the Surrey group [7]. The theoretical motivation for the spectator expansion derives from our present inability to calculate the full many-body problem. In this case an expansion is constructed within a multiple scattering theory predicated upon the idea that two-body interactions between the projectile and the target nucleons inside the nucleus play the dominant role. In the spectator expansion the rst order term involves two-body interactions between the projectile and one of the target nucleons, the second order term involves the projectile interacting with two target nucleons and so forth. Hence the expansion derives the ordering from the number of target nucleons interacting directly with the projectile, while the residual target nucleus remains `passive'. Due to the many-body nature of the free propagator for the the projectile + target system it is necessary to detail certain choices made with respect to the ordering in the spectator series. In our approach a theoretical treatment of this many-body propagator as a ected by the residual target nucleus is included in rst order.