Aspects of the momentum dependence of the equation of state and of the residualNNcross section, and their effects on nuclear stopping

Abstract

With the semiclassical Landau-Vlasov transport model we studied the stopping observable RE, the energy-based isotropy ratio, for the 129 Xe + 120 Sn reaction at beam energies spanning 12A to 100A MeV. We investigated the impacts of the nonlocality of the nuclear mean field, of the inmedium modified nucleon-nucleon (N N ) cross section and of the reaction centrality. A fixed set of model parameters yields RE values that favorably compare with the experimental ones, but only for energies below the Fermi energy EF . Above EF agreement is readily possible, but by a smooth evolution with energy of the parameter that controls the in-medium modification of N N cross section. By comparing the simulation correction factor F applied to the free N N cross section with the one deduced from experimental data [Phys. Rev. C 90, 064602 (2014)], we infer that the zero-range mean field almost entirely reproduces it. Also, in accordance with what has been deduced from experimental data, around EF a strong reduction of the free N N cross section is found. In order to test the impact of sampling central collisions by multiplicity an event generator (HIPSE) was used. We obtain that high multiplicity events are spread over a broad impact parameter range, but it turns out that this has a small effect on the observable RE and, thus, on F as well.

In-medium effects in central heavy ion collisions at intermediate energies

“…(6) becomes very small at low incident energy, the corresponding error bars on the in-medium N N cross section corrected from Pauli effect (green curve and area) are then very large. The in-medium nucleon-nucleon cross section is dramatically reduced (as observed in [9] and more recently in [10]) as compared to the one in vacuum around the Fermi energy, where the reduction factors f P auli and η are the more restrictive. As the incident energy increases, the in-medium cross section increases, tending asymptotically at the highest energies considered here ( 100 MeV/nucleon) towards the free nucleon-nucleon collisions cross section.…”

“…Well below E F , the one-body dissipation as predominant mode has been investigated by the study of fusion cross-sections [6,7]. Well above E F , the dissipation mode is increasingly induced by NN collisions [8][9][10]. Thus, a transition around E F is observed, and corresponds to the crossover between onebody to two-body dissipation [8,9].…”

Shear viscosity from nuclear stopping

“…Some authors simply take σ med NN as a fraction, e.g. half, of the free cross section [26][27][28][29]. The deficiency of this assumption is that the free NN cross sections are not recovered when the matter becomes sufficiently dilute.…”

Revisiting an extended-mean-field approach in heavy-ion collisions around the Fermi energy

“…These configurations, which may be called "events", by construction conserve the overall mean values of observables, respect the Pauli principle, and, otherwise, they correspond to the least biased N -body description compatible with the one-and two-body information contained in the ETDHF approach. Let us finally mention the fact that for the simulation measure having the sense of a genuine one-body quantity, nucleon aggregates which should not be experimentally detected must not be computed in (25). The selection of relevant events is performed through a cluster-recognition algorithm, which in this work has been adapted from Ref.…”