To facilitate the relativistic heavy-ion calculations based on transport equations, the binary collisions involving a Δ resonance in either the entrance channel or the exit channel are investigated within a Hamiltonian formulation of πNN interactions. An averaging procedure is developed to define a quasiparticle Δ* and to express the experimentally measured NN→πNN cross section in terms of an effective NN→NΔ* cross section. In contrast to previous works, the main feature of the present approach is that the mass and the momentum of the produced Δ*’s are calculated dynamically from the bare Δ⇆πN vertex interaction of the model Hamiltonian and are constrained by the unitarity condition. The procedure is then extended to define the effective cross sections for the experimentally inaccessible NΔ*→NN and NΔ*→NΔ* reactions. The predicted cross sections are significantly different from what are commonly assumed in relativistic heavy-ion calculations. The Δ potential in nuclear matter has been calculated by using a Bruckner-Hartree-Fock approximation. By including the mean-field effects on the Δ propagation, the effective cross sections of the NN→NΔ*, NΔ*→NN and NΔ*→NΔ* reactions in nuclear matter are predicted. It is demonstrated that the density dependence is most dramatic in the energy region close to the pion production threshold. © 1996 The American Physical Society.
- Received 20 February 1996
- Published in the issue dated September 1996
© 1996 The American Physical Society