Relativistic transport approach for nucleus-nucleus collisions based on a NJL lagrangian

We formulate a covariant transport approach for high energy nucleus-nucleus collisions where the real part of the hadron selfenergies is evaluated on the basis of a NJL-type Lagrangian for the quark degrees of freedom. The parameters of the model Lagrangian are fixed by the Gell-Mann, Oakes and Renner relation, the pion-nucleon \Sigma-term, the nucleon energy as well as the nuclear binding energy at saturation density \rho_0. We find the resulting scalar and vector selfenergies for nucleons to be well in line with either Dirac-Brueckner results or those from the phenomenological optical potential when accounting for a swelling of the nucleon at finite nuclear matter density. The imaginary part of the hadron selfenergies is determined by a string fragmentation model which accounts for the in-medium mass of hadrons in line with the chiral dynamics employed. The applicability of the 'chiral' transport approach is demonstrated in comparison with experimental data from SIS to SPS energies. The enhancement of the K^+/\pi^+ ratio in A + A collisions compared to p + A reactions at AGS energies is reproduced within the 'chiral' dynamics. Furthermore, detailed predictions for the stopping in Pb + Pb collisions at 153 GeV/A are presented

Orthotopic Liver Transplantation: Is There a Risk for Listeria monocytogenes Infection?

Immunosuppression of any kind is a known risk factor for infection with Listeria monocytogenes (L. monocytogenes). Particularly, patients with impaired liver function are at increased risk of developing an aggravated course of infection with this bacterial pathogen (see Nolla-Salas et al.; 2002 and Cabellos et al.; 2008). It is a well-known pathogen in immunocompromised patients, but has only seldom been reported following orthotopic liver transplantation. Invasion of the central nervous system presenting as meningitis or meningoencephalitis and bacteremia are the principal clinical manifestations of listerial infections (see Brouwer et al.; 2006). We present an account of a case of a patient who developed L. monocytogenes meningitis during the early period after liver transplantation

Direct Photons in Nuclear Collisions at FAIR Energies

Using the extrapolation of existing data estimations of prompt photon production at FAIR energies have been made. At $y=y_{c.m.}$ the rapidity density of prompt photons with $p_{t}>$ 1.5 GeV/c per central Au+Au event at 25 AGeV is estimated as $\sim 10^{-4}$ . With the planed beam intensity $10^{9}$ per second and 1% interaction probability, for 10% of most central events one can expect the prompt photon rate $\sim 10^{2}$ photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD) transport approach with implemented meson scatterings $\pi\rho\to\pi\gamma, \pi\pi\to\rho\gamma$ have been analyzed. Photons from short-living resonances (e.g. $\omega \to \pi^{0} \gamma$) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in the direct photon spectrum at $p_{t}=0.5 - 1$ GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions the HSD generator predicts, as a lower estimate, $\gamma_{direct}/\gamma_{\pi^{0}} \simeq$ 0.5% in the region $p_{t}=0.5 - 1$ GeV/c. At $p_{t}=1.5 - 2$ GeV/c $\gamma_{prompt}/\gamma_{\pi^{0}} \simeq$ 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly from the HSD predictions. The direct photon spectrum is very sensitive to the initial temperature parameter $T_{0}$ of the model. The 10 MeV increase in the $T_{0}$ value leads to $\sim$ 2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of Sciences, ITEP, Moscow, 26 - 30 November 200

Dileptons from the strongly-interacting Quark-Gluon Plasma within the Parton-Hadron-String-Dynamics (PHSD) approach

Dilepton production in In+In collisions at 158 AGeV is studied within the microscopic Parton-Hadron-Strings Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model (DQPM) matched to reproduce lattice QCD results in thermodynamic equilibrium. A comparison to the data of the NA60 Collaboration shows that the low mass dilepton spectra are well described by including a collisional broadening of vector mesons, while the spectra in the intermediate mass range are dominated by off-shell quark-antiquark annihilation in the nonperturbative QGP. In particular, the observed softening of the mT spectra at intermediate masses is reproduced.Comment: talk given at the 21st International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2009), to be published in Nucl.Phys.A, 4 pages, 3 figures, elsarticle styl

Influence of the in-medium pion dispersion relation in heavy ion collisions

We investigate the influence of medium corrections to the pion dispersion relation on the pion dynamics in intermediate energy heavy ion collisions. To do so a pion potential is extracted from the in-medium dispersion relation and used in QMD calculations and thus we take care of both, real and imaginary part of the pion optical potential. The potentials are determined from different sources, i.e. from the $\Delta$--hole model and from phenomenological approaches. Depending on the strength of the potential a reduction of the anti-correlation of pion and nucleon flow in non-central collisions is observed as well as an enhancement of the high energetic yield in transverse pion spectra. A comparison to experiments, in particular to $p_t$-spectra for the reaction Ca+Ca at 1 GeV/nucleon and the pion in-plane flow in Ne+Pb collisions at 800 MeV/nucleon, generally favours a weak potential.Comment: 25 pages, using REVTeX, 6 postscript figures; replaced by published versio

Resonance Model of πΔ→YK\pi \Delta \rightarrow Y K for Kaon Production in Heavy Ion Collisions

The elementary production cross sections $\pi \Delta \rightarrow Y K$ $(Y=\Sigma,\,\, \Lambda)$ and $\pi N \rightarrow Y K$ are needed to describe kaon production in heavy ion collisions. The $\pi N \rightarrow Y K$ reactions were studied previously by a resonance model. The model can explain the experimental data quite well \cite{tsu}. In this article, the total cross sections $\pi \Delta \rightarrow Y K$ at intermediate energies (from the kaon production threshold to3 GeV of $\pi \Delta$ center-of-mass energy) are calculated for the first time using the same resonance model. The resonances, $N(1710)\,I(J^P) = \frac{1}{2}(\frac{1}{2}^+)$ and $N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ for the $\pi \Delta \rightarrow \Sigma K$ reactions, and $N(1650)\, \frac{1}{2} (\frac{1}{2}^-)$, $N(1710)\, \frac{1}{2} (\frac{1}{2}^+)$ and $N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ for the $\pi \Delta \rightarrow \Lambda K$ reactions are taken into account coherently as the intermediate states in the calculations. Also t-channel $K^*(892) \frac{1}{2}(1^-)$ vector meson exchange is included. The results show that $K^*(892)$ exchange is neglegible for the $\pi \Delta \rightarrow \Sigma K$ reactions, whereas this meson does not contribute to the $\pi \Delta \rightarrow \Lambda K$ reactions. Furthemore, the $\pi \Delta \rightarrow Y K$ contributions to kaon production in heavy ion collisions are not only non-neglegible but also very different from the $\pi N \rightarrow Y K$ reactions. An argument valid for $\pi N \rightarrow Y K$ cannot be extended to $\pi \Delta \rightarrow Y K$ reactions. Therefore, cross sections for $\pi \Delta \rightarrow Y K$ including correctly the different isospins must beComment: ( Replaced with corrections of printing errors in the Table. ) 15 pages, Latex file with 4 figures, 1 figure is included in the text. A compressed uuencode file for 3 figures is appended. (A figure file format was changed.) Also available upon reques

Pion-nucleus reactions in a microscopic transport model

We analyse pion-nucleus reactions in a microscopic transport model of the BUU type, which propagates nucleons, pions, deltas and N(1440)-resonances explicitly in space and time. In particular we examine pion absorption and inelastic scattering cross sections for pion kinetic energies T(pi) =85-315MeV and various target masses. In general, the mass-dependence of the experimental data is well described for energies up to the delta-resonance (\approx 160 MeV) while the absorption cross sections are somewhat overestimated for the higher energies. In addition we study the possible dynamical effects of delta- and pion-potentials in the medium on various observables as well as alternative models for the in-medium delta-width.Comment: 31 pages, UGI-93-0

Reanalysis of antiproton production in proton-nucleus and nucleus-nucleus reactions at subthreshold energies

We reanalyse the production of $p\bar{p}$ pairs in proton-nucleus and nucleus-nucleus collisions employing novel elementary cross sections for baryon-baryon and pion-baryon production channels based on a boson-exchange model. In contrast to previous transport studies performed in the literature the secondary pion induced channel is found to be most important in both p+A and A+A collisions at subthreshold energies. A detailed comparison with the experimental data available indicates that sizeable attractive $\bar{p}$ potentials in the order of - 100 to - 150 MeV at normal nuclear matter density are needed to reproduce the size and shape of the experimental spectra.Comment: 25 pages, latex, including 15 ps-figures, UGI-97-21, submitted to Nucl. Phys.

Kaon versus Antikaon Production at SIS Energies

We analyse the production and propagation of kaons and antikaons in Ni + Ni reactions from 0.8--1.85 GeV/u within a coupled channel transport approach including the channels $BB \to K^+YN, \pi B\to K^+Y, BB \to NN K \bar{K}, \pi B\to N K\bar{K}, K^+B\to K^+B, \bar{K} B\to \bar{K}B, Y N\to \bar{K} NN, \pi \pi\to K \bar{K}$ as well as $\pi Y\to \bar{K}N$ and $\bar{K} N\to \pi Y$ for the antikaon absorption. Whereas the experimental $K^+$ spectra can be reproduced without introducing any selfenergies for the mesons in Ni + Ni collisions from 0.8 to 1.8 GeV/u, the $K^-$ yield is underestimated by a factor of 5--7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon masses as proposed by Kaplan and Nelson, the antikaon spectra can be reasonably well described.Comment: 16 pages, LaTeX, plus 12 postscript figures, submitted to Nucl. Phys.

Equilibration within a semiclassical off-shell transport approach

Equilibration times for nuclear matter configurations -- modelling intermediate and high energy nucleus-nucleus collisions -- are evaluated within the semiclassical off-shell transport approach developed recently. The transport equations are solved for a finite box in coordinate space employing periodic boundary conditions. The off-shell transport model is shown to give proper off-shell equilibrium distributions in the limit $t \to \infty$ for the nucleon and $\Delta$-resonance spectral functions. We find that equilibration times within the off-shell approach are only slightly enhanced as compared to the on-shell limit for the momentum configurations considered.Comment: 19 pages, LaTeX, including 4 postscript figures, submitted to Nucl. Phys.