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We study the cross section of ϕ meson production in proton-nucleus collisions. The decay width of the ϕ meson is affected by the change of the masses of the ϕ, K + and K − mesons in the medium. A strong attractive K − potential leads to a broadening of the ϕ meson, which results in a measurable change of the behavior of the cross section as a function of the target mass.

Small-angle correlations of pairs of nonidentical light charged particles produced in central collisions of heavy ions in the A= 100 mass region at a beam energy of 400 A· MeV are investigated with the FOPI detector system at GSI Darmstadt. The difference of longitudinal correlation functions with the relative velocity parallel and anti-parallel to the center-of-mass velocity of the pair in the central source frame is studied. This method allows extracting the apparent space-time differences of the emission of the charged particles. Comparing the correlations with results of a final-state interaction model delivers quantitative estimates of these asymmetries. Time delays as short as 1~fm/c or – alternatively – source radius differences of a few tenth fm are resolved. The strong collective expansion of the participant zone introduces not only an apparent reduction of the source radius but also a modification of the emission times. After correcting for both effects a complete sequence of the space-time emission of p, d, t, 3He, α particles is presented for the first time.

The mean multiplicity of intermediate mass fragments (IMF) {l angle}{ital M}{sub IMF}{r angle} produced by fragmentation of Au projectiles interacting with targets of C, Al, Cu, and Pb at an incident energy of {ital E}/{ital A}=600 MeV is compared to predictions of statistical multifragmentation and sequential evaporation models. The initial conditions for the calculations were provided by Boltzmann-Uehling-Uhlenbeck simulations. In the high excitation energy regime where the IMF multiplicity reaches its maximum the observed universal correlation between {l angle}{ital M}{sub IMF}{r angle} and the total charge {ital Z}{sub bound} of projectile fragments with charges {ital Z}{ge}2 cannot be reproduced by a sequential evaporation code. In this regime the data are better described by statistical decay calculations which assume the formation of an expanded nuclear system and a rather fast breakup.

In a transport model calculation we study some of the basic assumptions of thermal models, We find that at SIS energies the particles are mainly produced in a highly non-equilibrium situation, At freeze-out only nucleons are thermalized.

A generalized hydrodynamics is presented, which takes into account the anisotropy of the nucleon momentum distribution. The dynamics of the nuclear stopping process is studied in this framework.

Differential production cross sections of ${K}^{\ifmmode\pm\else\textpm\fi{}}$ mesons have been measured in $p+\mathrm{C}$ and $p+\mathrm{Au}$ collisions at 1.6, 2.5, and 3.5 GeV proton beam energy. At beam energies close to the production threshold, the ${K}^{\ensuremath{-}}$ multiplicity is strongly enhanced with respect to proton-proton collisions. According to microscopic transport calculations, this enhancement is caused by two effects: the strangeness exchange reaction $NY\ensuremath{\rightarrow}{K}^{\ensuremath{-}}NN$ and an attractive in-medium ${K}^{\ensuremath{-}}N$ potential at saturation density.

We compare multiplicities as well as rapidity and transverse momentum distributions of protons, pions and kaons calculated within presently available transport approaches for heavy ion collisions around 1 AGeV. For this purpose, three reactions have been selected: Au+Au at 1 and 1.48 AGeV and Ni+Ni at 1.93 AGeV., 15 pages, 13 figures, proceedings of Strange Quark Matter 2004, Cape Town, South Africa

The cross section for production of Phi mesons in proton-nucleus reactions is calculated as a function of the target mass. The decay width of the Phi meson is affected by the change of the masses of the Phi, K+ and K- mesons in the medium. A strong attractive K- potential leads to a measurable change of the behavior of the cross section as a function of of the target mass. Comparison between the kaon and electron decay modes are made., 4 pages, 1figure, new figure, new references

The cross sections for producing ${K}^{\ensuremath{-}}$ mesons in nucleon-hyperon elementary processes are estimated assuming one-pion exchange and using the experimentally known pion-hyperon cross sections. The results are implemented in a transport model which is applied to calculation of proton-nucleus collisions. In significant difference to earlier estimates for heavy-ion collisions the inclusion of the nucleon-hyperon cross section roughly doubles the ${K}^{\ensuremath{-}}$ production in near-threshold proton-nucleus collisions.

Correlations of two like charged pions emitted from a hot and charged spherically expanding nuclear system are investigated. The motion of the pions is described quantum mechanically using the Klein-Gordon equation which includes Coulomb field and pion absorption. Flow modifies the radial distribution of the source function and rescales the pion wave functions. The radii extracted from the correlation functions are calculated in sideward and outward direction as a function of the pair momentum. Comparison with recent measurements at SIS and AGS energies is made., 13 pages and 4 figures

Analysis of hard two-photon correlations measured in heavy-ion reactions at intermediate energies H.W.Barz1,2, B.Kämpfer1,2, GY. Wolf3,4, W. Bauer5 1Institut für Kern- und Hadronenphysik, FZ Rossendorf, PF 510119, 01314 Dresden, Germany 1Institut für Theoretische Physik, TU Dresden, Momrnsenstr. 13, 01062 Dresden, Germany 3GSI Darmstadt, PF 110552, 64220 Darmstadt, Germany 4KFKI RMKI Budapest, POB. 49, H-1525 Budapest, Hungary MSU Michigan, East Lansing, MI 48824, USA Abstract Recently reported measurements of hard photon correlations in the reactions 36Ar On 27Al at 95 A*MeV, 86Kr on natNi at 60 A*MeV, and 181Ta on 197Au at 39.5 A*MeV are analyzed. A Boltzmann-Ühling-Uhlenbeck transport model is used to describe the photon production by individual nucleon-nucleon collisions. In the lighter systems we find the best agreement with data when taking into account only the photons from first chance collisions of nucleons or photons produced during the Passage of the nuclei, while the model predicts also a considerable late-time emission of photons which leads to a depletion of the calculated correlation function. The accuracy of the present data daas not allow firm conclusions on the reliability of this late time evolution. Our inveatigatiions do not support a recently reported interference pattern in the heavy Ta + Au system.

In ultrarelativistic collisions of heavy ions a hot central region is formed that subsequently decays mostly into π mesons. One of the main goals of the theory of collisions is to trace the evolution of the hot initial zone until the stage when the freezeout occurs. For this purpose one has to study the dynamics of the pionic gas. One of the problems to be solved is, to what extent the observed pion spectra and, in particular, the enhancement at low momenta have to be associated with the formation of a hot and dense pionic zone right after the hadronization. In other words, one has to find out, whether in the rapidly expanding pion cloud the ππ collisions arc effective and frequent enough to thermalize the distribution of the pions. If not, the experimentally observed distribution of the pions might be remainder of the hadronization process itself and could give us, for example, information on whether the pions originate from a hadronizing plasma blob or not.

The transition from nuclear matter to quark matter in shock fronts is discussed. The relativistic shock equations are considered and applied to quark-matter production in dependence on the bag constant. The problem of shock splitting is discussed as a possible signature of the phase transition. One-dimensional hydrodynamical calculations for a two-phase system of nuclear matter and quark plasma are presented and compared to results of the shock equations for stable and unstable shock fronts.

Cross sections for production of pions, kaons and antikaons in heavy ion reactions are calculated in the framework of the hadrochemical model. For the reaction Ne on NaF satisfactory agreement to the measured data is reached in a wide range of energies. The importance of consecutive hadron-hadron collisions for the mass dependence is shown.

Taking into account a finite conversion rate the transition of nuclear matter to quark-gluon matter and vice versa is treated in a hydrodynamical model for heavy ion collisions. For fast conversion pure quark matter is formed for laboratory energies between 4 and 10 GeV per nucleon while below 4 GeV per nucleon matter stays in a mixed phase. Due to the large amount of latent heat the temperature does not exceed k T = 160 MeV.

A two-fluid model is presented which describes the interpenetration of nuclei colliding at ultra-relativistic energies. The two fluids are coupled by friction resulting from hadron-hadron collisions. The model calculations predict the deconfinement transition in the baryon-rich fragmentation region. The degree of the conversion and the maximum temperature depend sensitively on the characteristic time for the rearrangement of nuclear matter into the quark-gluon plasma.

Proton and pion spectra from relativistic heavy ion collisions are calculated in the framework of a hydrochemical model. An explanation of the striking absence of the delta decay pion peak in the observed pion spectra is suggested.

It is shown that subthreshold pion production in a collision between two nuclei at intermediate energy has to be attributed to an early stage of the collision and cannot take place together with a multifragmentation break-up at a later stage of the collision.

Because of nuclear transparency at beam energies relevant to quark plasma formation, the extension of phase equilibrium conditions for interpenetrating pieces of matter is investigated. Applying this thermodynamical formalism to the deconfinement transition a non-trivial change is found on the phase diagram, due to the relative velocity of the interpenetrating matter elements.

Strange particle production in heavy ion collisions is calculated in the framework of a hadrochemical model. It is compared with the results of cascade and fireball model calculations and experimental data. The importance of πN and πΔ collisions in producing kaons and hyperons is pointed out.

A common question in parallel programming is How to implement a program efficiently for a particular synchronization problem? Here we pose a more general question: Is a certain synchronization mechanism capable of implementing efficiently a particular synchronization problem represented by a program using another synchronization mechanism? We give a definition of “implementing efficiently” which measures efficiency by the amount of parallelism of the parallel programs. If this measure is reduced by the implementation the efficiency of the implementation is inferior. It is shown that some synchronization mechanisms cannot implement programs based on another mechanism without some loss in parallelism, i.e., a reduced measure. These results imply a power hierarchy (or efficiency hierarchy) of synchronization mechanisms. A further outcome of this paper is that simple synchronization mechanisms, with only a few variables, are capable of implementing any synchronization problem implementable by more powerful me...

The advantage of the continuum shell-model in describing nuclear reactions producing hypernuclei is discussed. Numerical results obtained within this model for the (K−,π−) reaction on9Be,12C,16O and40Ca are presented.

It is shown that the differential cross section of (p,n) reactions with 1 GeV protons corresponding to a Fermi-type transition between mirror nuclei is sensitive to the isovector component of the nuclear quadrupole moment because of the nuclear spin-re-orientation effect.

It is shown that spatial correlations between the constituent particles of a gas lead to roughly excluded volume type corrections in the equation of state. These corrections will appreciably change the hadrochemical composition of fireballs formed in heavy ion reactions.

The composite particle production in a heavy ion collision is calculated in the framework of a hadrochemical model. A critical comparison is performed between the produced entropy and the observables. The entropy production during the hadrochemical processes is found to be negligible.NUCLEAR REACTIONS Ne + NaF heavy ion collision, $E=0, 4\ensuremath{-}2.1$, calculated spectra $p$, $d$, ${\ensuremath{\pi}}^{+}$, van der Waals model, entropy.

Spherical hydrodynamical expansion and linear compression and expansion are calculated in viscous relativistic hydrodynamics. The break-up process subsequent to the hydrodynamical collective flow is also taken into account. The results lay the foundation of the blast-wave model and the comparison of the linear and spherical models with the experiment provides further evidence for the soft nuclear matter equation of state.

Ausgehend vom Matrixelement der Distorted Wave Born Approximation (DWBA) wird der Einflus der Austauschterme auf die Winkelverteilung der Reaktionen C13 (d, n) N11 und O17 (d, p1) O18 abgeschatzt. Dabei werden die gestorten Wellen durch ebene Wellen mit modifizierten Wellenzahlen ersetzt. Fur die Deuteronwellenfunktion werden die beiden Ansatze ν (χ) ˜ δ (χ) und ν (χ) ˜ konst. untersucht. Am Knockout-Prozes der B11 (d, p1) B10-Reaktionen zeigt sich, das der zweite Ansatz gunstiger ist. Die Rechnungen werden auf Winkel ≤ 60° beschrankt. Bei der C13 (d, n) N11-Reaktion verschieben die Austauschterme das Maximum der Winkelverteilung etwas nach kleineren Winkeln, wahrend der Wirkungsquerschnitt der Reaktion O17 (d, p1) O18 bei kleinen Winkeln deutlich angehoben wird.

In a fluid-dynamical model, the extra entropy production which arises from a nonequilibrium phase transition from nuclear to quark-gluon matter is calculated.

Systematic deviations from the Lorentzian approximation to the E1-giant dipole resonance (GDR) shape has been observed at the low energy side of the GDR /1,2/. The strength involved amounts to a few percent of the E1 sum rule,so this phenomenon is called pygmy resonance. A remarkable regularity has been mentioned by Lane /3/: The anomaly appears in mass number regions where empty single-particle states with l=0,1 are near the threshold. Applying the 1p-1h description the 1p-1h states containing the mentioned s or p-neutron particle states (threshold states) have unperturbed energies close to the energy of the anomaly. So these states may be saved from being coupled to the GDR. Such calculations /3,4,5/ performed in the pure 1p-1h shell model provide different amounts of the strength of the pygmy resonance as a function of the used residual interaction and basis.

Coulomb effects on $\pi^\pm$ and $K^\pm$ spectra in relativistic nuclear collisions are investigated. At collision energies around 1 GeV the ratio of $\pi^-$ to $\pi^+$ is enhanced several times at low transverse momenta but less at ultrarelativistic energies. We describe the ratios at SIS, AGS and SPS energies with simple analytic models as well as more elaborate numerical models incorporating the expansion dynamics. The Coulomb effect depends on the properties of the source after the violent collision phase and provides information on source sizes, freeze-out times, and expansion velocities. Comparison with results from HBT analyses are made. Predictions for $\pi^\pm$ and $K^\pm$ at RHIC and LHC energies are given., Comment: 22 pages including 12 figures. Added figure and revisions

The influence of the nuclear Coulomb field on transverse spectra of $\pi^+$ and $\pi^-$ measured in $Pb+Pb$ reactions at 158 A GeV has been investigated. Pion trajectories are calculated in the field of an expanding fireball. The observed enhancement of the $\pi^-/\pi^+$ ratio at small momenta depends on the temperature and transverse expansion velocity of the source, the rapidity distribution of the net positive charge, and mainly the time of the freeze-out., Comment: 11 pages including 2 figures

Within a transport code of BUU type the production of phi-mesons in the reactions Ni+Ni at 1.93 AGeV and Ru+Ru at 1.69 AGeV is studied. New elementary reaction channels rho+N(Delta) to phi+N and pi+N(1520) to phi+N are included. In spite of a substantial increase of the \phi multiplicities by these channels the results stay below the tentative numbers extracted from experimental data., Comment: 17 pages(LaTeX), two new figures added

Describing the expanding fireballs in a relativistic gas dynamical approach the formation of deuterons is calculated under consideration of inmedium corrections. The theoretical results are in good agreement with experimental data.