In-medium effects at low temperatures in the photon bremsstrahlung

Abstract

The infIuence of the dense nuclear medium on the process of photon bremsstrahlung in nuclear collisions at low excitation energies is investigated. The in-medium nucleon-nucleon scattering, &~matrix is incorporated in the calculations of photon bremsstrahlung cross section for nucleon-nucleus and nucleus-nucleus scattering cases. Calculations are performed in the soft photon approximation. It is shown that the Pauli blocking of intermediate scattering states and quasiparticle energy shifts due to the mean field interaction essentially suppress the photon bremsstrahlung cross section for temperatures T~10 MeV and densities n~n, (n, being. the nuclear saturation density). In the case of nucleus-nucleus collisions, when the photons are emitted from the thermalized zone, a temperature and density dependent reduction factor for the bremsstrahlung rate is calculated. It implies a typical bremsstrahlung rate which is -15% of that in the free scattering case. PACS number(s): 25.70.Lm, 21.65.+f, 24. 10. -i, 24.90.+d

A direct probe of the in-medium pn scattering cross section

“…It was noted that for nuclear bremsstrahlung, a strong suppression or coherence of the bremsstrahlung cross section were observed in comparison with predictions of transport models that include bremsstrahlung on the basis of quasi-free nucleon-nucleon collisions [31,32]. In this study, we use the BUU transport model [33] with an isospin-dependent in-medium reduced nucleon-nucleon (NN) cross section [4,6] to treat the in-medium bremsstrahlung semiclassically [34]. The energy and isospin dependent free-space NN cross sections σ f ree N N are taken from the experimental data.…”

Suppression of Soft Nuclear Bremsstrahlung in Proton-Nucleus Collisions

“…A value g ≈ 0.5 is expected to describe the mean time between the first and second collision, i.e., τ ≈ 8 fm/c. Averaging over the time distribution (1/τ )exp(−t/τ ) we derive the following quenching factor, whose analytical form is motivated by several theoretical calculations [5,9,23]:…”