Correlations in the in-medium nucleon-nucleon cross section

The influence of the ground state correlations on the in-medium nucleon-nucleon cross section is investigated in the framework of an extended Brueckner-Hartree-Fock theory of nuclear matter. The effect of the correlations is to overwhelm the suppression of the in-medium NN cross section already established in previous approximations. Moreover the resulting cross section exceeds largely, particularly for neutron-proton scattering, the free-space values in the low energy range (up to 200-250 MeV) for nuclear medium densities up to two times the saturation density.