Antikaon production in A+A collisions at SIS energies within an off-shell G-matrix approach

Abstract

The production and propagation of antikaons -described by dynamical spectral functions A h (X, P , M 2 ) as evaluated from a coupled channel G-matrix approachis studied for nucleus-nucleus collisions at SIS energies in comparison to the conventional quasi-particle limit and the available experimental data using off-shell transport theory. We find that the K − spectra for 12 C + 12 C and 58 N i + 58 N i at 1.8 A·GeV remain underestimated in the G-matrix approach as in the on-shell quasiparticle approximation whereas the preliminary spectra for Au + Au at 1.5 A·GeV are well described in both limits. This also holds approximately for the K − rapidity distributions in semi-central collisions of N i + N i at 1.93 A·GeV. However, in all limits considered there is no convincing description of all spectra simultaneously. Our off-shell transport calculations, furthermore, demonstrate that the strongest in-medium effects should be found for low antikaon momenta in the center-of-mass frame, since the deceleration of the antikaons in the attractive Coulomb and nuclear potentials and the propagation to the on-shell mass induces a net shift and squeezing of the K − spectra to the low momentum regime.

Dynamical quasiparticles properties and effective interactions in the sQGP

“…Whereas the real part of the selfenergies can be related to mean-field potentials, the imaginary parts of Π provide information about the lifetime and/or reaction rate of time-like 'particles' [6]. In principle, off-shell transport equations are available in the literature [29][30][31], but have been applied only to dynamical problems where the width of the quasiparticles stays moderate with respect to the pole mass [32]. On the other hand, the studies of Peshier [33,34] indicate that the effective degrees of freedom in a partonic phase should have a width γ in the order of the pole mass M already slightly above T c .…”

Strangeness at high μB: Recent data from FOPI and HADES

“…In Fig. 2 values for v 1 measured by the FOPI collaboration in central Ni+Ni collisions at 1.9 AGeV are plotted as function of rapidity for positive and negative kaons and protons together with predictions of HSD [17] and IQMD [11] models. Near target rapidity K + -mesons show a collective in-plane deflection in the direction opposed to that of protons.…”

S= −1 meson-baryon interaction in hot and dense nuclear matter: chiral symmetry, many-body and unitarization for a road to GSI/FAIR

“…We note that the η and Ξ channels where not included in the analysis of [6], based on an implementation ofKN dynamics from the Jülich meson-exchange model in the Giessen-Frankfurt Hadron-String-Dynamics (HSD) transport model. Another important asset of our approach is that, whereas it achieves a good description of K − p vacuum low-energy scattering observables (such as cross sections, scattering lengths and branching ratios at threshold) with a minimal number of parameters, the model is highly predictive also in the K − n sector.…”

“…The calculation of dynamical quantities in transport theory requires that the pertinent reaction rates or transition probabilities are folded with the spectral functions of the particles in the initial and final states [6]. We discuss below these transition probabilities including medium effects in hot and dense matter for severalKN two-body processes which play a key role in accessing the near sub-threshold region in antikaon production dynamics.…”

“…The properties of both K andK close to threshold energy have also been thoroughly investigated in HICs at SIS energies [2][3][4]6]. The analysis of experimental data in conjunction with microscopic transport approaches has allowed to draw solid conclusions regarding the production mechanisms and the freeze-out conditions of strange mesons.…”