Off shell behaviour of the in medium nucleon-nucleon cross section

The properties of nucleon-nucleon scattering inside dense nuclear matter are investigated. We use the relativistic Brueckner-Hartree-Fock model to determine on-shell and half off-shell in-medium transition amplitudes and cross sections. At finite densities the on-shell cross sections are generally suppressed. This reduction is, however, less pronounced than found in previous works. In the case that the outgoing momenta are allowed to be off energy shell the amplitudes show a strong variation with momentum. This description allows to determine in-medium cross sections beyond the quasi-particle approximation accounting thereby for the finite width which nucleons acquire in the dense nuclear medium. For reasonable choices of the in-medium nuclear spectral width, i.e. $\Gamma\leq 40$ MeV, the resulting total cross sections are, however, reduced by not more than about 25% compared to the on-shell values. Off-shell effect are generally more pronounced at large nuclear matter densities.Comment: 31 pages Revtex, 12 figures, typos corrected, to appear in Phys. Rev.

Effect of the Real Potential on <Sup>12</Sup>C-<Sup>12</Sup>C Reaction Cross Section

The effect of the potential on the 12C-12C reaction cross section at different bombarding energies is studied by taking the distance of closest approach instead of the impact parameter in the Glauber optical limit. At low energies E1ab/A 20 MeV the Coulomb distortion of the trajectories does enhance the results. The addition of the attractive nuclear potential gives good agreement with the experiment at energies E1ab/A 20-200 MeV