Asymmetric colliding nuclear matter approach in heavy ion collisions

Abstract

The early stage of a heavy ion collision is governed by local non-equilibrium momentum distributions which have been approximated by colliding nuclear matter configurations, i.e. by two Lorentz elongated Fermi ellipsoids. This approach has been extended from the previous assumption of symmetric systems to asymmetric 2-Fermi sphere configurations, i.e. to different densities. This provides a smoother transition from the limiting situation of two interpenetrating currents to an equilibrated system. The model is applied to the dynamical situations of heavy ion collisions at intermediate energies within the framework of relativistic transport (RBUU) calculations. We find that the extended colliding nuclear matter approach is more appropriate to describe collective reaction dynamics in terms of flow observables, in particular, for the elliptic flow at low energies.

Kaon production in heavy ion reactions at intermediate energies

“…up to maximally 3 ρ 0 . This fact is further consistent with the findings of Gaitanos et al [209,264] where a good description of v 1 and v 2 data at energies between 0.2 and 0.8 AGeV has been found in RBUU calculations based on DBHF mean fields. However, as pointed out in Refs.…”

“…A detailed comparison to v 1 and v 2 data below 1 AGeV from FOPI [262] and KaoS [263] favors again a relatively soft EOS with a momentum dependence close to that obtained from microscopic DBHF calculations [198,209,264]. In Fig.…”

“…However, as pointed out in Refs. [209,18,264,211] is thereby essential to account for non-equilibrium effects and the momentum dependence of the forces which softens the EOS compared to the equilibrium case shown in Fig. 51.…”

Excitation function of elliptic flow in Au+Au collisions and the nuclear matter equation of state

“…Other observables, like directed flow [28,34] or strange particle yields [35], which may probe the collision in complementary ways, need to be simultaneously reproduced as well. Attempts in this direction have already been made [4,23,25]. It is unlikely that a narrow bound on EoS can be derived based on one single observable.…”

Interplay of anisotropies of momentum distribution and mean field in heavy-ion collisions

“…In addressing the first stages of collisions, we consider the situation of two separated Fermi spheres in momentum space, for projectile and target. Several efforts in the literature [16][17][18], with the goal of coping with the early stage momentum anisotropies, specifically consider the latter type of superposition.…”