The NN→NΔ cross section in nuclear matter Original Research Article

We present calculations of the NN→NΔ cross section in nuclear matter within the one-pion exchange model taking into account pion collectivity, vertex renormalization by the contact nuclear interactions and Dirac effective masses of the baryons due to coupling with the scalar σ field. Introducing the Dirac effective masses leads to an in-medium reduction of the cross section. The experimental data on pion multiplicities from the collisions of Ca+Ca, Ru+Ru and Au+Au at 0.4–1.5 A GeV are well described by BUU calculations with the in-medium cross section.