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The dynamics of hot and dense nuclear matter is discussed from the microscopic transport point of view. The basic concepts of the Hadron-String-Dynamical transport model (HSD)-derived from Kadanoff-Baym equations in phase phase-are presented as well as 'highlights' of HSD results for different observables in heavy-ion collisions from 100 A MeV (SIS) to 21 A TeV(RHIC) energies. Furthermore, a novel extension of the HSD model for the description of the partonic phase-the Parton-Hadron-String-Dynamics (PHSD) approach-is introduced. PHSD includes a nontrivial partonic equation of state-in line with lattice QCD-as well as covariant transition rates from partonic to hadronic degrees of freedom. The sensitivity of hadronic observables to the partonic phase is demonstrated for relativistic heavy-ion collisions from the FAIR/NICA up to the RHIC energy regime. [ABSTRACT FROM AUTHOR]

The production of K+-mesons in proton-nucleus collisions from 1.0 to 2.3 GeV is analyzed with respect to one-step nucleon-nucleon (NN?NYK+) and two-step ?-nucleon (?N?K+ YN) or pion-nucleon (pN?K+ Y) production channels on the basis of a coupled-channel (CBUU) transport approach including the kaon final-state-interactions (FSI). Momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are included as well as K+ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental K+ spectra taken at COSY-Jülich. Our systematic analysis of K+ spectra from12C,63Cu,107Ag and197Au targets as well as their momentum differential ratios gives a repulsive K+ potential of 20±5 MeV at normal nuclear matter density. [ABSTRACT FROM AUTHOR]

We propose a nonperturbative resummation scheme for the four-point connected quark-antiquark Green’s functionG4 that shows how the Bethe-Salpeter equation may be “unquenched” with respect to quark-antiquark loops. This mechanism allows to dynamically account for hadronic meson decays and multiquark structures whilst respecting the underlying symmetries. An initial approximation to the four-point Schwinger-Dyson equation - suitable for phenomenological application - is examined numerically in a couple of aspects. It is demonstrated that this approximation explicitly maintains the correct asymptotic limits and contains the physical resonance structures in the near timelike region in the quark-antiquark channel. [ABSTRACT FROM AUTHOR]

The effect of quark-gluon vertex dressing on the ground-state masses of theu/d-quark pseudoscalar, vector and axialvector mesons is considered with the Dyson-Schwinger equations. This extends the ladder-rainbow Bethe-Salpeter kernel to two-loops. To render the calculations feasible for this exploratory study, we employ a simple infrared dominant model for the gluon exchange that implements the vertex dressing. The resulting model, involving two distinct representations of the effective gluon exchange kernel, preserves both the axial-vector Ward-Takahashi identity and charge conjugation symmetry. Numerical results confirm that the pseudoscalar meson retains its Goldstone boson character. The vector meson mass, already at a very acceptable value at ladder level, receives only 30?MeV of attraction from this vertex dressing. For the axial-vector states, which are about 300?MeV too low in ladder approximation, the results are mixed: The 1+- state receives 290?MeV of repulsion, but the 1++ state is lowered further by 30?MeV. The exotic channels 0-- and 1-+ are found to have no states below 1.5?GeV in this model. [ABSTRACT FROM AUTHOR]

The production and decay of vector mesons (p, w) in pA and AA reactions is studied with particular emphasis on their in-medium spectral functions. It is explored within transport calculations if hadronic in-medium decays like Π+π- or π°γ might provide complementary information to their dilepton (e+e-) decays. Whereas the π+&pi,- signal from the p-meson is found to be strongly distorted by pion rescattering, the w-meson Dalitz decay to π°γ appears promising even for more heavy nuclei in 7A and pA reactions. Furthermore, the influence of nucleon and kaon/antikaon potentials on the K± yields and spectra in pA collisions is calculated and compared to the recent data from the ANKE Collaboration. [ABSTRACT FROM AUTHOR]

The lifetime of the Λ-hyperon in heavy hypernuclei measured in proton-Au, -Bi and -U collisions by the COSY-13 Collaboration at COSY-Jülich has been analyzed to yield τΛ = (145±11) ps. This value for τΛ is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, albeit much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological Δ I = 1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2-3 standard deviations). Such large differences indicate that at least one of the assumptions in these models is not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the Δ I = 1/2 rule is discarded in the nonmesonic Λ decay. [ABSTRACT FROM AUTHOR]

The predictions for the production of nuclides and particles in proton-induced reactions are important e.g. for the detailed design of spallation neutron sources or accelerator-driven-systems. Computational tools are required that are able to describe quantitatively the two-stage process i.e. intra-nuclear cascade followed by evaporation-fission. The first stage is a highly non-equilibrated process in which incoming proton deposits in hot residual nucleus both excitation energy and angular momentum. The CBUU transport model calculation for few targets, for the proton energy range 0.4-2.0 GeV are presented, with the idea to find global parametrizations for the distributions of charge, mass, excitation energy, angular momentum of hot residual nuclei. [ABSTRACT FROM AUTHOR]

Presents a correction to the article "Transport Analysis of K+ Production in Proton-Nucleus Reactions," that appeared in a previous issue of the "European Physics Journal."

Using the Quark-Gluon Strings Model --combined with Regge phenomenology-- we perform a comparative analysis of Λ, Σ0, Λ(1520) and Θ+ production in binary reactions induced by photon, pion and proton beams on the nucleon. We find that the existing experimental data on the γ p↦ K+Λ differential and total cross-sections can be described very well by the model for photon energies 1-16 GeV and - t < 2 GeV2 assuming a dominant contribution of the K* Regge trajectory. Moreover, using the same parameters we also reproduce the total γ p↦ K+Σ0 and γ p↦ K+Λ(1520) cross-sections suggesting a “universality” of the Regge model. In order to check the consistency of the approach we evaluate the differential and total cross-sections for the reaction π- p↦ K0Λ which is also found to be dominated by the K* Regge trajectory. Using the apparent “universality” of the Regge model we extend our scheme to the analysis of the binary reactions γ p↦¯0Θ+, π- p↦ K-Θ+ and pp↦Σ+Θ+ as well as the exclusive and inclusive Θ+ production in the reactions pp↦ p¯0Θ+ and pp↦Θ+ X. Our detailed studies demonstrate that Θ+ production does not follow the “universality” principle, thus suggesting an essentially different internal structure of the exotic baryon relative to conventional hyperons or hyperon resonances. [ABSTRACT FROM AUTHOR]

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. It is found that the forward-backward angle asymmetry predicted by the model is confirmed by the recent data at different photon energies from JLab. New calculations for polarization observables, the cross-section asymmetry Σ and the polarization transfer Cz', for photon energies (1.2-6) GeV are presented and compared with the data available up to 2 GeV. [ABSTRACT FROM AUTHOR]

: We study the perspectives of resonant charmonium production in p + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(2S) and Ψ(3770) on various nuclei, their propagation and decay to dileptons and D + D in the medium and vacuum, respectively, employing parametrizations for the D,D self-energies taken from QCD sum rule studies. The elastic and inelastic interactions of the charmonia and open-charm mesons in the medium are taken into account, too. It is found that the D,D invariant-mass spectra from light and heavy nuclei are not sufficiently sensitive to the in-medium properties of the Ψ(2S) and Ψ(3770). However, a “suppression” of low-mass dileptons from the Ψ(3770) might be seen experimentally as well as a small broadening of the Ψ(2S) dilepton spectra. [ABSTRACT FROM AUTHOR]

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different 7-energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5-6 GeV are presented and compared with the available data. [ABSTRACT FROM AUTHOR]

Event-by-event fluctuations of the K/π, K/p, and p/π ratio in central AA collisions have been studied for SPS and RHIC energies. The Hadron-String-Dynamical transport approach (HSD) can qualitatively reproduce the measured excitation function for the K/π ratio fluctuations. The di-jet azimuthal correlations also have been investigated within the HSD model. We found that the suppression of the away-side jet in the hadronic mediumis not enough to explain the experimental data from RHIC. The additional suppression should be attributed to a quark-gluon plasma produced in heavy-ion collisions. [ABSTRACT FROM AUTHOR]

An investigation of color fields that arise in collisions of relativistic heavy ions reveals that, in the non-Abelian case, a change in the color charge leads to the appearance of an extra term that generates a sizable contribution of color-charge glow in chromoelectric and chromomagnetic fields. The possibility of the appearance of a color echo in the scattering of composite color particles belonging to the dipole type is discussed. Arguments are adduced in support of the statement that such effects are of importance in simulating the first stage of ultrarelativistic heavy-ion collisions,where the initial parton state is determined by a high nonequilibrium parton density and by strong local color fluctuations. [ABSTRACT FROM AUTHOR]

Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model, we analyze near-threshold production of a0(980)-mesons in the reaction NN → dK &Kmacr; as well as the background of non-resonant K &Kmacr;-pair production. We argue that the reaction pp → dK+ &Kmacr;0 at an energy release Q ≤ 100MeV is dominated by the intermediate production of the a0(980)-resonance. At larger energies the non-resonant K+ &Kmacr;0-pair production — where the kaons are produced in a relative P-wave — becomes important. The effects of final-state interactions are evaluated in a unitarized scattering length approach and found to be in the order of a 20% suppression close to threshold. Thus, in present experiments at the Cooler Synchrotron COSY-Jülich for Q ≤ 107 MeV the a0+ signal can reliably be separated from the non-resonant K+ &Kmacr;00 background. [ABSTRACT FROM AUTHOR]

We consider near-threshold a[sub 0](980)-meson production in πN and NN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN reactions are used to calculate the contribution of the a[sub 0] meson to the cross sections and invariant KK mass distributions of the reactions pp → pnK[sup +]K[sup 0] and pp → ppK[sup +]K[sup –]. It is found that the experimental observation of a[sub 0][sup +] mesons in the reaction pp → pnK[sup +]K[sup 0] is much more promising than the observation of a[sub 0][sup 0] mesons in the reaction pp → ppK[sup +]K[sup –]. Effects of isospin violation in the reactions pN → da[sub 0], pd → [sup 3]He([sup 3]H)a[sub 0], and dd → [sup 4]Hea[sub 0], which are induced by a[sub 0](980)–f[sub 0](980) mixing, are also analyzed.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We study the kinetic and chemical equilibration in 'infinite' parton matter within the Parton-Hadron-String Dynamics transport approach. The 'infinite' matter is simulated within a cubic box with periodic boundary conditions initialized at different energy densities. Particle abundances, kinetic energy distributions, and the detailed balance of the off-shell quarks and gluons in the strongly-interacting quarkgluon plasma are addressed and discussed. [ABSTRACT FROM AUTHOR]

Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions π-→ K0Λ and π-p→ D Λ+c which are dominated by the contributions of the K* and D* Regge trajectories, respectively. The spin structure of the amplitudes is described by introducing Reggeized Born terms. It is found that the existing data for the reaction π-p →K 0;Λ are in reasonable agreement with the model predictions. To describe the absolute values of the cross-sections it is necessary to introduce also suppression factors which can be related to absorption corrections. Furthermore, assuming the SU(4) symmetry to hold for Regge residues and the universality of absorption corrections we calculate the cross-section of the reaction π-p→D-Λ+C. Employing the latter results from π-p reactions we then estimate the contributions of the pion exchange mechanism to the cross-sections of the reactions NN → NKA and NN → NDACand compare them with the contributions of the K and D exchanges. We find that the NN reactions are dominated not by pion exchange but by K and D exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants gND&lambdac= gNKA we analyze also the production of leading Λc-hyperons in the reaction NN ↠ΛcX. It is shown that the non-perturbative mechanism should give an essential contribution to theΛc yield for x &Ge;0.5. [ABSTRACT FROM AUTHOR]