Event anisotropy in 4.2A GeV/c C+C collisions

The directed and elliptic flow of protons and negative pions in 4.2A GeV/c C+C collisions is studied using the Fourier analysis of azimuthal distributions. It is found that the protons exhibit pronounced directed flow, while the flow of pions is either non existent or too weak to be detected experimentally. Also, it is found that in the entire rapidity interval the elliptic flow is very small if not zero. These results are confirmed by the Quark-Gluon-String Model (QGSM) and the relativistic transport model (ART 1.0), except that these models predict very weak antiflow of pions. The more detailed comparison with the QGSM suggests that the decay of resonances and rescattering of secondaries dominantly determine the proton and negative pion flow at this energy.Comment: 7 pages, 3 figures, TeX file changed from double to single-spacin

How many of the scaling trends in pppp collisions will be violated at sqrt{s_NN} = 14 TeV ? - Predictions from Monte Carlo quark-gluon string model

Multiplicity, rapidity and transverse momentum distributions of hadrons produced both in inelastic and nondiffractive $pp$ collisions at energies from $\sqrt{s} = 200$\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon string model (QGSM). Good agreement with the available experimental data up to $\sqrt{s} = 13$\,TeV is obtained, and predictions are made for the collisions at top LHC energy $\sqrt{s} = 14$\,TeV. The model indicates that Feynman scaling and extended longitudinal scaling remain valid in the fragmentation regions, whereas strong violation of Feynman scaling is observed at midrapidity. The Koba-Nielsen-Olesen (KNO) scaling in multiplicity distributions is violated at LHC also. The origin of both maintenance and violation of the scaling trends is traced to short range correlations of particles in the strings and interplay between the multistring processes at ultrarelativistic energies

Monte Carlo model for nuclear collisions from SPS to LHC energies

A Monte Carlo model to simulate nuclear collisions in the energy range going from SPS to LHC, is presented. The model includes in its initial stage both soft and semihard components, which lead to the formation of color strings. Collectivity is taken into account considering the possibility of strings in color representations higher than triplet or antitriplet, by means of string fusion. String breaking leads to the production of secondaries. At this point, the model can be used as initial condition for further evolution by a transport model. In order to tune the parameters and see the results in nucleus-nucleus collisions, a naif model for rescattering of secondaries is introduced. Results of the model are compared with experimental data, and predictions for RHIC and LHC are shown.Comment: LaTeX, 48 pages, 6 tables, 15 postscript figures included using epsfi

Cross-sections for nuclide production in 56Fe target irradiated by 300, 500,750, 1000, 1500, and 2600 MeV protons compared with data on hydrogen target irradiation by 300, 500, 750, 1000, and 1500 MeV/nucleon 56Fe ions

Cross-sections for radioactive nuclide production in 56Fe(p,x) reactions at 300, 500, 750, 1000, 1500, and 2600 MeV were measured using the ITEP U-10 proton accelerator. In total, 221 independent and cumulative yields of products of half-lives from 6.6 min to 312 days have been obtained via the direct-spectrometry method. The measured data have been compared with the experimental data obtained elsewhere by the direct and inverse kinematics methods and with calculations by 15 codes, namely: MCNPX (INCL, CEM2k, BERTINI, ISABEL), LAHET (BERTINI, ISABEL), CEM03 (.01, .G1, .S1), LAQGSM03 (.01, .G1, >.S1), CASCADE-2004, LAHETO, and BRIEFF. Most of our data are in a good agreement with the inverse kinematics results and disprove the results of some earlier activation measurements that were quite different from the inverse kinematics measurements. The most significant calculation-to-experiment differences are observed in the yields of the A<30 light nuclei, indicating that further improvements in nuclear reaction models are needed, and pointing out as well to a necessity of more complete measurements of such reactions.Comment: 53 pages, 9 figures, 6 tables, only pdf file, submitted to Phys. Rev.

The initial state of ultra-relativistic heavy ion collision

A model for energy, pressure and flow velocity distributions at the beginning of ultra-relativistic heavy ion collisions is presented, which can be used as an initial condition for hydrodynamic calculations. Our model takes into account baryon recoil for both target and projectile, arising from the acceleration of partons in an effective field, produced in the collision. The typical field strength (string tension) for RHIC energies is about 5-12 GeV/fm, what allows us to talk about "string ropes". The results show that a QGP forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. Such initial conditions may lead to the creation of "antiflow" or "third flow component".Comment: 28 pages, 9 figures. The presentation has been changed considerably. Some parts of the model have been reformulated, what led to modifications in several equations: (20-38), Apps. A, B. All the figures have been changed from 100 GeV/nucl initial energy to the achieved RHIC energy of 65 GeV/nucl. The last subplots in the Figs. 3, 4, 5, 6 present E=T^{00} in the laboratory frame now, instead of the energy density in the local rest frame, e, shown in the initial version. We also added the App. C to clarify the transformation from space-time to lightcone coordinates and bac

Production of spectator hypermatter in relativistic heavy-ion collisions

We study the formation of large hyper-fragments in relativistic heavy-ion collisions within two transport models, DCM and UrQMD. Our goal is to explore a new mechanism for the formation of strange nuclear systems via capture of hyperons by relatively cold spectator matter produced in semi-peripheral collisions. We investigate basic characteristics of the produced hyper-spectators and evaluate the production probabilities of multi-strange systems. Advantages of the proposed mechanisms over an alternative coalescence mechanism are analysed. We also discuss how such systems can be detected taking into account the background of free hyperons. This investigation is important for the development of new experimental methods for producing hyper-nuclei in peripheral relativistic nucleus-nucleus collisions, which are now underway at GSI and are planned for the future FAIR and NICA facilities.Comment: 28 pages, including 10 figures. Submitted to Phys. Rev.

Study of ππ\pi\pi correlations at LHC and RHIC energies in pppp collisions within the quark-gluon string model

The Quark Gluon String Model (QGSM) reproduces well the global characteristics of the $pp$ collisions at RHIC and LHC, e.g., the pseudorapidity and transverse momenta distributions at different centralities. The main goal of this work is to employ the Monte Carlo QGSM for description of femtoscopic characteristics in $pp$ collisions at RHIC and LHC. The study is concentrated on the low multiplicity and multiplicity averaged events, where no collective effects are expected. The different procedures for fitting the one-dimensional correlation functions of pions are studied and compared with the space-time distributions extracted directly from the model. Particularly, it is shown that the double Gaussian fit reveals the contributions coming separately from resonances and from directly produced particles. The comparison of model results with the experimental data favors decrease of particle formation time with rising collision energy.Comment: 9 pages, 14 figures, 2 table