Theoretical study of electronic transitions in relativistic heavy-ion collisions

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It is known from the study of Toshima and others that special account of the long-range of Coulomb interactions is not needed in the non-relativistic coupled-channel approach. We have shown that this is not the case for relativistic ion-atom collisions and distorted-wave formalism must be used even for coupled-channel method in order to make the transition matrix well-defined. It was demonstrated by numerical calculations based on the distorted-wave method that the cross sections for the system U^<92+>+U^<91+> change more than a factor of two by this effect. The symmetric eikonal approximation, which is a symmetrized version of the traditional eikonal theory, has been used widely because of the simplicity of the formula. We pointed out from both analytic and numerical calculations that the symmetric eikonal formula does not satisfy the correct coulomb boundary conditions and it gives unphysically large spin-flip cross sections owing to this defect. It is widely known that the second-or … More der contribution becomes dominant at high energies for electron capture processes. As a result the differential cross section shows a sharp peak at a critical angle and this peak is called the Thomas peak. Although the dominance of the second-order term implies the inadequacy of the perturbation theory itself, all of the theoretical studies for the Thomas mechanism were based on the perturbation theory. We developed a new coupled-channel code based on Gauss-type orbital expansion and succeeded in producing the Thomas peak by nonperturbative method for the first time. By this study it was demonstrated that the Thomas peak is shifted to smaller scattering angle side and a third-order process is contributing significantly owing to a multiscattering effect. Besides we carried out the classical trajectory Monte Carlo calculation for the Thomas mechanism and showed that the Thomas peak is unexpectedly missing in the pure classical treatment. Exact calculation of the second-Born terms was also realized for the first time for rearrangement collisions into exited states and destructive and constructive interference effects were reported. Less