Refine
Year of publication
Document Type
- Article (200)
- Preprint (155)
- Conference Proceeding (4)
- Report (1)
- Working Paper (1)
Has Fulltext
- yes (361)
Is part of the Bibliography
- no (361)
Keywords
- Kollisionen schwerer Ionen (40)
- heavy ion collisions (33)
- equation of state (11)
- Quark-Gluon-Plasma (10)
- Zustandsgleichung (9)
- quark-gluon plasma (9)
- Hadron (8)
- Quark Gluon Plasma (8)
- heavy ion collision (8)
- QGP (7)
- Quanten-Chromodynamik (7)
- UrQMD (7)
- quark (7)
- Energie (6)
- Meson (6)
- Quark (6)
- heavy-ion collisions (6)
- meson (6)
- quark gluon plasma (6)
- relativistic (6)
- QCD (5)
- Quantum Chromodynamic (5)
- collision (5)
- energy (5)
- nucleon (5)
- Dirac (4)
- Drell-Yan (4)
- Kollision (4)
- LHC (4)
- QMD (4)
- Quark Materie (4)
- RQMD (4)
- SPS (4)
- gluon (4)
- hadronic (4)
- hydrodynamisches Modell (4)
- nuclear reactions (4)
- quark matter (4)
- relativistic quantum molecular dynamics (4)
- schwere Ion Kollision (4)
- Bremsstrahlung (3)
- EOS (3)
- Materie (3)
- Molekulare Dynamik (3)
- Neutronenstern (3)
- Nukleon (3)
- Strahl (3)
- Ultrarelativistic Quantum Molecular Dynamics (3)
- Zustandsgleichungen (3)
- baryon (3)
- bremsstrahlung (3)
- hadronic matter (3)
- heavy ion colliders (3)
- hydrodynamical model (3)
- jet (3)
- neutron star (3)
- nuclei (3)
- relativistisch (3)
- schwere Ion-Kollision (3)
- Dilepton (2)
- Dirac-Brueckner theory (2)
- Dirac-Brückner Theorie (2)
- Gluon (2)
- Heavy ion collisions (2)
- Kaon (2)
- Kerne (2)
- Lagrangian (2)
- Nambu Jona-Lasinio Modell (2)
- Nambu Jona-Lasinio model (2)
- Nucleon (2)
- Partikelspektren (2)
- Pion (2)
- Plasma (2)
- Quanten Chromodynamik (2)
- Quantenchromodynamik (2)
- Quantum Chromodynamics (2)
- Quantum Molecular Dynamics (2)
- Quark gluon Plasma (2)
- Quark-Gluon Plasma (2)
- Teilchen (2)
- Temperatur (2)
- UrQMD Modell (2)
- Walecka model (2)
- antibaryon (2)
- bound state (2)
- degrees of freedom (2)
- dense matter (2)
- dichte Materie (2)
- dilepton (2)
- freeze out (2)
- hadron (2)
- hadronische Materie (2)
- hydrodynamic description (2)
- kaon (2)
- kinetic equation (2)
- kinetische Gleichung (2)
- matter (2)
- nuclear matter (2)
- nucleus-nucleus collisions (2)
- particle spectra (2)
- pion (2)
- plasma (2)
- quark-gluon-plasma (2)
- relativistische (2)
- schwere Ione (2)
- statistical coalescence model (2)
- statistisches Fusionsmodell (2)
- strange hadronic matter (2)
- temperature (2)
- ultrarelativistisch (2)
- ultrarelativistische (2)
- (QGP) (1)
- 13C(16O (1)
- 17O) (1)
- 20Ne + 238U (1)
- 232Th (1)
- 234-238U calculated B (E2) values (1)
- AGS (1)
- Abhängigkeit von der Dichte (1)
- Absorption (1)
- Anti-Kaon (1)
- Antikaon (1)
- Antinukleonen (1)
- Ar + Pb (800 MeV/nucleon) relativistic heavy-ion reactions (1)
- Ar+Ca (1)
- Ausfrieren (1)
- BEVALAC (1)
- Baryon Resonance (1)
- Baryon-Resonanz (1)
- Bjorken Modell (1)
- Bjorken model (1)
- Boltzmann-Uehling-Uhlenbeck (1)
- Boltzmann-Uehling-Uhlenbeck Gleichung (1)
- Boltzmann-Uehling-Uhlenbeck equation (1)
- Bose (1)
- Bose-simulated pion production (1)
- Charmonium Produktion (1)
- Charmonium production (1)
- Cluster distribution (1)
- Cluster integrals (1)
- Conservation Laws (1)
- Deuteron (1)
- Dichte (1)
- Dielectron (1)
- Dielektron (1)
- Distributed software development (1)
- Drell-Yan production (1)
- Drell-Yan ratio (1)
- Drell-Yan-Prozess (1)
- Dynamik (1)
- Dyson-Schwinger equation (1)
- E1ab=400 MeV/nucleon fluid dynamics (1)
- Elab=393 MeV/nucleon (1)
- Elementarteilchen (1)
- Elementary particle (1)
- Equation of state (1)
- Ereignisschwankungen (1)
- Erhaltungsgesetz (1)
- Event-by-event fluctuations (1)
- Freeze Out (1)
- Freeze out (1)
- Freiheitsgrad (1)
- Freiheitsgrade (1)
- Geometrical modelling (1)
- Geometrisches Modellieren (1)
- Gluon-Plasma (1)
- Hadron Gas Modell (1)
- Hadron Materie (1)
- Hadronenbeschleuniger (1)
- Hartree (1)
- Homogeneous nucleation (1)
- Hypermaterie (1)
- IQMD Modell (1)
- IQMD model (1)
- In-Medium Zerfall (1)
- J/psi Erhöhung (1)
- J/psi Unterdrückung (1)
- J/psi enhancement (1)
- J/psi mesons (1)
- J/psi suppression (1)
- J/psi yield (1)
- J/ϕ (1)
- K-Meson (1)
- Kaons (1)
- Kern-Kern Kollision (1)
- Kern-Kern Kollisionen (1)
- Kernkollision (1)
- Kernmaterie (1)
- Kollisionen des schweren Ions (1)
- Korrelation (1)
- Lagrangian . equation of state (1)
- Large Hadron Collider (1)
- Lepton (1)
- Local thermodynamical equilibrium (1)
- Lorentz (1)
- Lorentz contraction (1)
- MEMOs (1)
- Massenspektrum (1)
- Monte Carlo Modell (1)
- Monte Carlo model (1)
- Monte-Carlo model for relativistic heavy ion collisions (1)
- Nambu Jona Lasinio Modell (1)
- Nambu Jona Lasinio model (1)
- Nambu-Jona-Lasinio (1)
- Nambu-Jona-Lasinio Modell (1)
- Nambu-Jona-Lasinio model (1)
- Ne+U (1)
- Neutronensterne (1)
- Nichtgleichgewicht (1)
- Nichtumkehrbarkeit (1)
- Non-equilibrium effects (1)
- Nucleus–nucleus collisions (1)
- OMD (1)
- Objectoriented technology (1)
- Objektorientierte Technologie (1)
- Particle Spectra (1)
- Particle interactions (1)
- Partikel-Wechselwirkungen (1)
- Pb+Pb collisions (1)
- Phasenübergang (1)
- Photon (1)
- Pion Gas (1)
- Pion-Produktion (1)
- QCD medium (1)
- QCD plasma (1)
- QGP hadrons phase transition (1)
- QGP signals (1)
- QMC (1)
- QMD Modell (1)
- QMD model (1)
- QSM (1)
- Quanten Chromodynamic (1)
- Quanten-Molekular-Dynamic (1)
- Quanten-Molekular-Dynamik (1)
- Quanten-Molekulardynamik (1)
- Quantendynamik (1)
- Quantum (1)
- Quantum chromodynamics (1)
- Quark Antiquark (1)
- Quark-Sterne (1)
- Quarkonium (1)
- RHIC (1)
- Raum Zeit (1)
- Relativistic Heavy Ion Collider (1)
- Relativistic heavy-ion reactions (1)
- Relativistisch (1)
- Rho-Meson (1)
- SHM (1)
- SU (3) - Modell (1)
- SU (3) - Symmetrie (1)
- SU (3) Modell (1)
- SU(3) model (1)
- SU(3)-model (1)
- SU(3)-symmetry (1)
- Schwankung (1)
- Simulation (1)
- Skalarpotential (1)
- Software engineering (1)
- Softwaretechnik (1)
- Statistical model (1)
- Strangelets (1)
- Strangeness production (1)
- Super Proton Synchrotron (1)
- Teilchenbeschleuniger (1)
- Teilchenspektren (1)
- Teilchenverteilung (1)
- Transportmodell (1)
- URQMD (1)
- Ultra-relativistic Quantum Molecular Dynamic (1)
- Ultra-relativistic Quantum Molecular Dynamics model (1)
- Ultrarelativisitic Quantum Molecular Dynamics model (1)
- Ultrarelativisitisches (1)
- Ultrarelativistic Quantum Molecular Model (1)
- Ultrarelativistisches Quant Molekular Dynamik (1)
- Ultrarelativistisches Quant Molekulares Modell (1)
- UrQMD model (1)
- Van der Waals (1)
- Van der Waals model (1)
- Vektorpotential (1)
- Verbreitung (1)
- Vielkörperkorrelationen (1)
- Walecka Modell (1)
- Walecka-Modell (1)
- Walecka-model (1)
- Zeitabhängig (1)
- Zusammenstoß (1)
- absorption (1)
- angular distribution (1)
- anti-kaon (1)
- anti-nucleons (1)
- antikaon (1)
- asymmetric two-center shell model (1)
- begrenzte Kerne (1)
- bestimmte Zustände (1)
- binaryfission (1)
- bound states (1)
- broadening (1)
- calculated level diagrams (1)
- charm and bottom Produktion (1)
- charm and bottom production (1)
- chemical (1)
- chemical freezeout (1)
- chemisches Ausfrieren (1)
- chiral SU (3) (1)
- chiral SU(3) (1)
- chiral SU(3) model (1)
- cold baryon rich matter (1)
- cold quark matter (1)
- collective model (1)
- color current (1)
- coloured quark dynamic (1)
- compressible flow (1)
- conservation law (1)
- conservation laws (1)
- cross sections (1)
- deconfinement phase transition (1)
- dense (1)
- density and momentum dependence (1)
- deuteron (1)
- dileptons (1)
- directed flow (1)
- double differential cross sections (1)
- energie (1)
- finite nuclei (1)
- flow (1)
- flow of nucleons (1)
- fluid dynamics (1)
- fluid dynamics with thermal breakup (1)
- freezeout (1)
- gluon plasma (1)
- hadron hadron Kollision (1)
- hadron hadron collision (1)
- hadron matter (1)
- hadron yield (1)
- hadronic fluctuation (1)
- hadronic freeze-out (1)
- hard-core (1)
- heat conduction (1)
- heavy ion scattering (1)
- heavy ions (1)
- heiße Kernmaterie (1)
- heiße Pion Materie (1)
- heiße und dichte Kernmaterie (1)
- heiße und dichte Materie (1)
- high energie (1)
- hitze (1)
- hohe Energie (1)
- homogene Nukleation (1)
- hot (1)
- hot and dense matter (1)
- hot and dense nuclear matter (1)
- hot hypernuclear matter (1)
- hot pion matter (1)
- hydrodynami (1)
- hydrodynamic model (1)
- hypermatter (1)
- hyperon (1)
- hyperonic Materie (1)
- hyperonic matter (1)
- ideal gas (1)
- ideales Gas (1)
- in-medium decay (1)
- in-medium properties (1)
- integro-differential equation (1)
- irreversibility state (1)
- kalte dunkle Materie (1)
- kaons (1)
- kinetic energy (1)
- kinetisches Ausfrieren (1)
- kinetisches Modell (1)
- kollidieren (1)
- lange hadron collider (1)
- lepton (1)
- lokales thermodynamisches Gleichgewicht (1)
- many-body correlations (1)
- mass spectra (1)
- meson mass (1)
- microscopic model (1)
- microscopic transport theory (1)
- mikroskopische Transporttheorie (1)
- mikroskopisches Modell (1)
- molecular theory of nucleon transfer (1)
- multicluster fission (1)
- neutron stars (1)
- niobium (1)
- non-equilibrium quantum field dynamics (1)
- nuclear (1)
- nuclear cold fission (1)
- nuclear collisions (1)
- nuclear hydrodynamics (1)
- nuclear shadowing (1)
- nuclear system (1)
- nucleon and nuclear cross sections (1)
- nucleon spectra (1)
- nuclera reactions (1)
- offene charm Produktion (1)
- open and hidden charm (1)
- open and hidden charm production (1)
- open charm production (1)
- open charm yield (1)
- pQCD (1)
- particle collisions (1)
- particle distribution (1)
- particle ratios (1)
- particles (1)
- partonic (1)
- perturbative Quantum Chromodynamic (1)
- photon (1)
- pion gas (1)
- quantum chromodynamic (1)
- quantum molecular dynamic (1)
- quantum molecular dynamics model (1)
- quantum statistical model (1)
- quark antiquark (1)
- quark gluon Plasma (1)
- quark shadowing (1)
- quark-meson coupling model (1)
- quarkonium (1)
- reich (1)
- relativistic heavy ion collider (1)
- relativistic heavy ion collision (1)
- relativistic heavy ion reactions (1)
- relativistic heavy-ion reactions (1)
- relativistic transport model (1)
- relativistische schwere Ion Kollision (1)
- relativistischer Schwerionen-Zusammenstoßer (1)
- rho meson (1)
- rich (1)
- saddle point shapes (1)
- scalar potential (1)
- schwere Ion-Kollisionen (1)
- schwere Ionen Kollision (1)
- second cluster integral (1)
- space-momentum correlation (1)
- space-time (1)
- statistical model (1)
- statistisches Modell (1)
- strange (1)
- strange quark star (1)
- strangelets (1)
- strangeness (1)
- superheavy (1)
- superheavy nuclei (1)
- superschwer (1)
- superschwere Kerne (1)
- system (1)
- thermal (1)
- thermalization (1)
- time dependent (1)
- true ternary fission (1)
- two-proton correlations (1)
- ultra-relativistic heavy ion collision (1)
- ultrarelativistic (1)
- ultrarelativistic energie (1)
- ultrarelativistic heavy-ion collision (1)
- ultrarelativistische Kollision des schweren Ionen (1)
- ultrarelativistische energie (1)
- van der Waals (1)
- vector mesons (1)
- vector potential (1)
- viscosity (1)
- zweite Gruppenintegral (1)
Institute
The extension of the Periodic System into hitherto unexplored domains - anti- matter and hypermatter - is discussed. Starting from an analysis of hyperon and single hypernuclear properties we investigate the structure of multi-hyperon objects (MEMOs) using an extended relativistic meson field theory. These are contrasted with multi-strange quark states (strangelets). Their production mechanism is stud- ied for relativistic collisions of heavy ions from present day experiments at AGS and SPS to future opportunities at RHIC and LHC. It is pointed out that abso- lutely stable hypermatter is unlikely to be produced in heavy ion collisions. New attention should be focused on short lived metastable hyperclusters ( / 10 10s) and on intensity interferometry of multi-strange-baryon correlations.
Abstract: The e ect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The e ect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This e ect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation (RHA), where the baryon self energy is modified due to interactions with both the non-strange ( ) and the strange ( ) scalar fields.
The wave function of a spheroidal harmonic oscillator without spin-orbit interaction is expressed in terms of associated Laguerre and Hermite polynomials. The pairing gap and Fermi energy are found by solving the BCS system of two equations. Analytical relationships for the matrix elements of inertia are obtained function of the main quantum numbers and potential derivative. They may be used to test complex computer codes one should develop in a realistic approach of the fission dynamics. The results given for the 240 Pu nucleus are compared with a hydrodynamical model. The importance of taking into account the correction term due to the variation of the occupation number is stressed.
Potential energy surfaces are calculated by using the most advanced asymmetric two-center shell model allowing to obtain shell and pairing corrections which are added to the Yukawa-plus-exponential model deformation energy. Shell effects are of crucial importance for experimental observation of spontaneous disintegration by heavy ion emission. Results for 222Ra, 232U, 236Pu and 242Cm illustrate the main ideas and show for the first time for a cluster emitter a potential barrier obtained by using the macroscopic-microscopic method.
Complex fission phenomena
(2004)
Complex fission phenomena are studied in a unified way. Very general reflection asymmetrical equilibrium (saddle point) nuclear shapes are obtained by solving an integro-differential equation without being necessary to specify a certain parametrization. The mass asymmetry in binary cold fission of Th and U isotopes is explained as the result of adding a phenomenological shell correction to the liquid drop model deformation energy. Applications to binary, ternary, and quaternary fission are outlined.
We developed a three-center phenomenological model,able to explain qualitatively the recently obtained experimental results concerning the quasimolecular stage of a light-particle accompanied fission process. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way,a new minimum of a short-lived molecular state appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments.The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the $^{10}$Be and $^{12}$C accompanied fission of $^{252}$Cf are roughly estimated to be the order of 1 ns, and 1 ms, respectively.
A three-center phenomenological model able to explain, at least from a qualitative point of view, the difference in the observed yield of a particle-accompanied fission and that of binary fission was developed. It is derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment is obtained by increasing continuously the separation distance, while the radii of the light fragment and of the light particle are kept constant. During the first stage of the deformation one has a two-center evolution until the neck radius becomes equal to the radius of the emitted particle. Then the three center starts developing by decreasing with the same amount the two tip distances. In such a way a second minimum, typical for a cluster molecule, appears in the deformation energy. Examples are presented for $^{240}$Pu parent nucleus emitting $\alpha$-particles and $^{14}$C in a ternary process.
A very general saddle point nuclear shape may be found as a solution of an integro-differential equation without giving apriori any shape parametrization. By introducing phenomenological shell corrections one obtains minima of deformation energy for binary fission of parent nuclei at a finite (non-zero) mass asymmetry. Results are presented for reflection asymmetric saddle point shapes of thorium and uranium even-mass isotopes with A=226-238 and A=230-238 respectively.
We study the effects of isovector-scalar meson delta on the equation of state (EOS) of neutron star matter in strong magnetic fields. The EOS of neutron-star matter and nucleon effective masses are calculated in the framework of Lagrangian field theory, which is solved within the mean-field approximation. From the numerical results one can find that the delta-field leads to a remarkable splitting of proton and neutron effective masses. The strength of delta-field decreases with the increasing of the magnetic field and is little at ultrastrong field. The proton effective mass is highly influenced by magnetic fields, while the effect of magnetic fields on the neutron effective mass is negligible. The EOS turns out to be stiffer at B < 10^15G but becomes softer at stronger magnetic field after including the delta-field. The AMM terms can affect the system merely at ultrastrong magnetic field(B > 10^19G). In the range of 10^15 G - 10^18 G the properties of neutron-star matter are found to be similar with those without magnetic fields.
Conventional cluster and virial expansions are generalized to momentum dependent interparticle potentials. The model with Lorentz contracted hard core potentials is considered, e.g. as hadron gas model. A Van der Waals-type model with a temperature dependent excluded volume is derived. Lorentz contraction effects at given temperature are stronger for light particles and make their effective excluded volume smaller than that of heavy ones.
We compare different models for hadronic and quark phases of cold baryon rich matter in an attempt to find a deconfinement phase transition between them. For the hadronic phase we consider Walecka type mean field models which describe well the nuclear saturation properties. We also use the variational chain model which takes into account correlation effects. For the quark phase we consider the MIT bag model, the Nambu Jona-Lasinio and the massive quasiparticle models. By comparing pressure as a function of baryon chemical potential we find that crossings of hadronic and quark branches are possible only in some exceptional cases while for most realistic parameter sets these branches do not cross at all. Moreover, the chiral phase transition, often discussed within the framework of QCD motivated models, lies in the region where the quark phases are unstable with respect to the hadronic phase. We discuss possible physical consequences of these findings.
We study properties of compact stars with the deconfinement phase transition in their interiors. The equation of state of cold baryon-rich matter is constructed by combining a relativistic mean-field model for the hadronic phase and the MIT Bag model for the deconfined phase. In a narrow parameter range two sequences of compact stars (twin stars), which differ by the size of the quark core, have been found. We demonstrate the possibility of a rapid transition between the twin stars with the energy release of about 10 ^52 ergs. This transition should be accompanied by the prompt neutrino burst and the delayed gamma-ray burst.
We discuss the possibility of producing a new kind of nuclear system by putting a few antibaryons inside ordinary nuclei. The structure of such systems is calculated within the relativistic mean field model assuming that the nucleon and antinucleon potentials are related by the G parity transformation. The presence of antinucleons leads to decreasing vector potential and increasing scalar potential for the nucleons. As a result, a strongly bound system of high density is formed. Due to the significant reduction of the available phase space the annihilation probability might be strongly suppressed in such systems.
Chemically non equilibrated quark antiquark matter is studied within the Nambu Jona-Lasinio model. The equations of state of non strange (q = u, d) and strange (q = s) qq systems are calculated in the mean field approximation. The existence of metastable bound states with zero pressure is predicted at finite densities and temperatures T 50 MeV. It is shown that the minimum energy per particle occurs for symmetric systems, with equal densities of quarks and antiquarks. At T = 0 these metastable states have quark number densities of about 0.5 fm 3 for q = u, d and of 1 fm 3 for q = s. A first order chiral phase transition is found at finite densities and temperatures. The critical temperature for this phase transition is approximately 75 MeV (90 MeV) for the non strange (strange) baryon free quark antiquark matter. For realistic choices of parameters, the model does not predict a phase transition in chemically equilibrated systems. Possible decay channels of the metastable qq droplets and their signatures in relativistic heavy ion collisions are discussed.
Properties of dense quark matter in and out of chemical equilibrium are studied within the SU(3) Nambu Jona-Lasinio model. In addition to the 4 fermion scalar and vector terms the model includes also the 6 fermion flavour mixing interaction. First we study a novel form of deconfined matter, meso-matter, which is composed of equal number of quarks and antiquarks. It can be thought of as a strongly compressed meson gas where mesons are melted into their elementary constituents, quarks and antiquarks. Strongly bound states in this quark antiquark matter are predicted for all flavour combinations of qq pairs. The maximum binding energy reaches up to 180 MeV per qq pair for mixtures with about 70% of strange (s¯s) pairs. Equilibrated baryon rich quark matter with various flavour compositions is also studied. In this case only shallow bound states appear in systems with a significant admixture(about 40%) of strange quarks (strangelets). Their binding energies are quite sensitive to the relative strengths of scalar and vector interactions. The common property of all these bound states is that they appear at high particle densities when the chiral symmetry is nearly restored. Thermal properties of meso-matter as well as chemically equilibrated strange quark matter are also investigated. Possible decay modes of these bound states are discussed.
We study the bremsstrahlung of virtual omega mesons due to the collective deceleration of nuclei at the initial stage of an ultrarelativistic heavy ion collision. It is shown that electromagnetic decays of these mesons may give an important contribution to the observed yields of dileptons. Mass spectra of e+e and µ+µ pairs produced in central Au+Au collisions are calculated under some simplifying assumptions on the space time variation of the baryonic current in a nuclear collision process. Comparison with the CERES data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a noticeable fraction of the observed e+e pairs in the intermediate region of invariant masses. Sensi tivity of the dilepton yield to the in medium modification of masses and widths of vector mesons is demonstrated.
According to the Walecka mean field theory of nuclear interaction the collective mutual deceleration of the colliding nuclei gives rise to the bremsstrahlung of real and virtual ! mesons. It is shown that decays of these mesons may give a noticeable contribution to the observed yields of the baryon antibaryon pairs, dileptons and pions. Excitation functions and rapidity distributions of particles produced by this mechanism are calculated under some simplifying assumptions about the space time variation of meson fields in nuclear collisions. The calculated multiplicities of coherently produced particles grow fast with the bombarding energy, reaching a saturation above the RHIC bombarding energy. In the case of central Au+Au collisions the bremsstrahlung mechanism becomes comparable with particle production in incoherent hadron hadron collisions above the AGS energies. The rapidity spectra of antibaryons and pions exhibit a characteristic two hump structure which is a consequence of incomplete projectile target stopping at the initial stage of the reaction. The predicted distribution of e+e pairs has a strong peak at invariant masses Me+e < 0.5 GeV.
Collective bremsstrahlung of vector meson fields in relativistic nuclear collisions is studied within the time dependent Walecka model. Mutual deceleration of the colliding nuclei is described by introducing the e ective stopping time and average rapidity loss of baryons. It is shown that electromagnetic decays of virtual ω mesons produced by bremsstrahlung mechanism can provide a substantial contribution to the soft dilepton yield at the SPS bombarding energies. In particular, it may be responsible for the dilepton enhancement observed in 160 AGev central Pb+Au collisions. Suggestions for future experiments to estimate the relative contribution of the collective mechanism are given.
Antibaryons bound in nuclei
(2004)
We study the possibility of producing a new kind of nuclear systems which in addition to ordinary nucleons contain a few antibaryons (B = p, , etc.). The properties of such systems are described within the relativistic mean field model by employing G parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from 4He to 208Pb. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus resulting in a significant increase of its binding energy and local compression. Noticeable e ects remain even after the antibaryon coupling constants are reduced by factor 3 4 compared to G parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that due to significant reduction of the reaction Q values, the in medium annihilation rates should be strongly suppressed leading to relatively long lived antibaryon nucleus systems. Multi nucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound B + A systems in pA reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing multi quark antiquark clusters is discussed. PACS numbers: 25.43.+t, 21.10.-k, 21.30.Fe, 21.80.+a