Microscopic analysis of K^+-nucleus elastic scattering based on K^+N phase shifts

We investigate $K^{+}$-nucleus elastic scattering at intermediate energies within a microscopic optical model approach. To this effect we use the current $K^{+}$-nucleon {\it (KN)} phase shifts from the Center for Nuclear Studies of the George Washington University as primary input. First, the {\it KN} phase shifts are used to generate Gel'fand-Levitan-Marchenko real and local inversion potentials. Secondly, these potentials are supplemented with a short range complex separable term in such a way that the corresponding unitary and non-unitary {\it KN} $S$ matrices are exactly reproduced. These {\it KN} potentials allow to calculate all needed on- and off-shell contributions of the $t$ matrix,the driving effective interaction in the full-folding $K^{+}$-nucleus optical model potentials reported here. Elastic scattering of positive kaons from $^{6}$Li, $^{12}$C, $^{28}$Si and $^{40}$Ca are studied at beam momenta in the range 400-1000 MeV/{$c$}, leading to a fair description of most differential and total cross section data. To complete the analysis the full-folding model, three kinds of simpler $t\rho$ calculations are considered and results discussed. We conclude that conventional medium effects, in conjunction with a proper representation of the basic {\it KN} interaction are essential for the description of $K^{+}$-nucleus phenomena.Comment: 11 pages, 1 table, 12 figures, submitted to PR

Functional medium-dependence of the nonrelativistic optical model potential

By examining the structure in momentum and coordinate space of a two-body interaction spherically symmetric in its local coordinate, we demonstrate that it can be disentangled into two distinctive contributions. One of them is a medium-independent and momentum-conserving term, whereas the other is functionally --and exclusively-- proportional to the radial derivative of the reduced matrix element. As example, this exact result was applied to the unabridged optical potential in momentum space, leading to an explicit separation between the medium-free and medium-dependent contributions. The latter does not depend on the strength of the reduced effective interaction but only on its variations with respect to the density. The modulation of radial derivatives of the density enhances the effect in the surface and suppresses it in the saturated volume. The generality of this result may prove to be useful for the study of surface-sensitive phenomena.Comment: 11 pages, 5 figures, submitted to Phys. Rev.