We investigate stopping and baryon transport in central relativistic Pb + Pb and Au + Au collisions. At energies reached at the CERN Super Proton Synchrotron [sqrt(s_NN) = 6.3-17.3 GeV] and at RHIC (62.4 GeV), we determine the fragmentation-peak positions from the data. The resulting linear growth of the peak positions with beam rapidity is in agreement with our results from a QCD-based approach that accounts for gluon saturation. No discontinuities in the net-proton fragmentation peak positions occur in the expected transition region from partons to hadrons at 6-10 GeV.
We study the production of proton, antiproton and net-proton at \AGS, \SPS and \RHIC within the framework non-uniform flow model(NUFM) in this paper. It is found that the system of RHIC has stronger longitudinally non-uniform feature than AGS and SPS, which means that nuclei at RHIC energy region is much more transparent. The NUFM model provides a very good description of all proton rapidity at whole AGS, SPS and RHIC. It is shown that our analysis relates closely to the study of nuclear stopping and longitudinally non-uniform flow distribution of experiment. This comparison with AGS and SPS h…
We investigate the energy dependence of hadron production and of stopping power based on HIJING/BBbar v2.0 model calculations. Pseudorapidity spectra and transverse momentum distributions for produced charged particles as well as net baryons (per pair of partcipants) and their rapidity loss are compared to data at RHIC and predictions for LHC energies are discussed.
A new geometrical scaling method with gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate the net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distribution…
This paper reviews our recent findings on the dynamics of transport of baryon number in proton-induced reactions at the CERN SPS. These are put in a more general context of the present understanding of baryon stopping phenomena up to LHC and cosmic ray energies. The implications of our studies, advantages to be provided by modern and high quality experimental data, and perspectives of new measurements are shortly discussed.
We propose a non-equilibrium hadronic model to interpret the observed excitation function of kaon-to-pion ratios in nuclear collisions at AGS and SPS energies. The crucial assumption of our model is that due to stronger stopping at lower energies the lifetime of the fireball is prolonged because the system has to build up the longitudinal expansion from internal pressure.
We study the dimuon yield from open charm decays in the intermediate mass region(IMR) in heavy-ion collisions at the CERN-SPS energy. We find that final state rescatterings which broaden the $m_T$ spectrum of charmed mesons can enrich the part of the phase space covered by the NA50 experiment, thus leading to an apparent enhancement of IMR dileptons within the acceptance of the experiment. Such an enhancement increases with the dimuon invariant mass and the single muon energy cut-off.
Inclusive cross sections for pion production in $pp$ collisions are calculated for the first time fully based on unintegrated gluon, quark and antiquark distributions (uPDF). We use recently developed Kwieciński uPDF's and different phenomenological fragmentation functions (FF) from the literature. In addition to the $gg \to g$ diagram we include also $g q \to q$ and $q g \to q$ diagrams for inclusive parton production. The cross section for pions is obtained then by convoluting the inclusive parton distributions and FFs. Applications for SPS and RHIC are shown.
We investigate consequences of local energy-momentum conservation for initial eccentricity coefficients in heavy ion collisions at not too high energies relevant for CERN SPS and RHIC BES. Different models of energy density available for pion production are considered. We study dependence of eccentricity coefficients on space-time rapidity for different impact parameters. The naive formula how to define eccentricities breaks with our initial conditions and must be corrected. We predict considerable eccentricities for $ε_{1,2,3,4}$ and specific dependence on space-time rapidity as well as on im…
Collective transverse flow in heavy-ion collisions at incident energies E_{lab} = (1 -160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). Simulations are performed with purely hadronic equation of state (EoS). At the AGS energies the flow turns out to be sensitive to the stopping power of nuclear matter rather than only to the stiffness of the EoS. When the stopping power is fixed to reproduce other observables, the flow data favor more and more soft EoS with the incident energy rise, which can be associated with ``a transition from hadronic to string matter'' reported in the Had…
The UrQMD transport model, version 3.4, is used to study the new experimental data on transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, $p$ and $\bar p$ produced in inelastic $p+p$ interactions at SPS energies, recently published by the NA61/SHINE Collaboration. The comparison of model predictions to these new measurements is presented as a function of collision energy for central and forward particle rapidity intervals. In addition, the inverse slope parameters characterizing the transverse momentum distributions are extracted from the predicted spectra and compared to the corresponding va…
Chiral Lagrangians are used to compute the production rate of photons from the hadronic phase of relativistic nuclear collisions. Special attention is paid to the role of the pseudovector a_1 meson. Calculations that include reactions with strange mesons, hadronic form factors and vector spectral densities consistent with dilepton production, as well as the emission from a quark-gluon plasma and primordial nucleon-nucleon collisions, reproduce the photon spectra measured at the Super Proton Synchrotron (SPS). Predictions for the Relativistic Heavy Ion Collider (RHIC) are made.
Anisotropic transverse flow is studied in Pb+Pb and Au+Au collisions at SPS and RHIC energies. The centrality and transverse momentum dependence at midrapidity of the elliptic flow coefficient v_2 is calculated in the hydrodynamic and low density limits. Hydrodynamics is found to agree well with the RHIC data for semicentral collisions up to transverse momenta of 1-1.5 GeV/c, but it considerably overestimates the measured elliptic flow at SPS energies. The low density limit LDL is inconsistent with the measured magnitude of v_2 at RHIC energies and with the shape of its p_t-dependence at both …
By colliding ultrarelativistic ions, one achieves presently energy densities close to the critical value, concerning the formation of a quark-gluon-plasma. This indicates the importance of fluctuations and the necessity to go beyond the investigation of average events. Therefore, we introduce a percolation approach to model the final stage ($τ> 1$ fm/c) of ion-ion collisions, the initial stage being treated by well-established methods, based on strings and Pomerons. The percolation approach amounts to finding high density domains, and treating them as quark-matter droplets. In this way, we hav…
The centrality dependence of rapidity distributions of pions in Pb+Pb reactions can be understood by imposing local energy-momentum conservation in the longitudinal "fire-streaks" of excited matter. With no tuning nor adjustment to the experimental data, the rapidity distribution of pions produced by the fire-streak which we obtained from Pb+Pb collisions reproduces the shape of the experimental pion rapidity distribution in p+p interactions, measured by the NA49 Collaboration at the same energy. The observed difference in the absolute normalization of this distribution can be explained by the…
The features of net baryon productions and collective flow in relativistic heavy-ion collisions at energies reached at the CERN Large Hadron Collider (LHC), BNL Relativistic Heavy Ion Collider (RHIC), CERN Super Proton Synchrotron (SPS) and BNL Alternating Gradient Synchrotron (AGS) with the model of Non-Uniform Flow Model(NUFM) are systematically studied in this paper. Especially we predict the feature of net baryon productions and collective flow at LHC $\sqrt{s_{NN}}$=5500 GeV basing on the detailed study of that at RHIC $\sqrt{s_{NN}}$=62.4 and 200GeV. The dependencies of the features of b…
Physics of charmonium suppression in nuclear collisions drastically changes between the energies of SPS and RHIC. Mechanisms suppressing charmonia at SPS are reviewed, neither of which is important at RHIC. On the other hand, coherence, or shadowing of c-quarks and gluons barely seen at SPS, become a dominant effect at RHIC providing a much stronger suppression. A onset of coherence at Fermilab energies explains the observed cross section ratio steeply falling at large Feynman x_F. In nuclear collisions variation of charmonium suppression with x_F suggests a sensitive probe for QGP.
We study the production of charmonia and charmed hadrons in nucleus-nucleus collisions at SPS, RHIC, and LHC energies within the framework of the statistical hadronization model. Results from this model are compared to the measured yields and centrality dependence of J/psi production at SPS and RHIC energies. We explore and contrast the centrality dependence of the production of mesons with open and hidden charm at SPS, RHIC, and LHC. The sensitivity of the results to various input parameters is analyzed in detail for RHIC energy.
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…
The significance of thermal dilepton radiation at intermediate invariant masses (1GeV<M<3GeV) in ultrarelativistic heavy-ion collisions is investigated. At CERN-SpS energies, a consistent explanation of the excess observed by NA50 can be given. At RHIC energies the thermal signal is dominated by early emission indicative for QGP formation. Chemical under-saturation effects and the competition with open-charm contributions are addressed.
Higher-order pQCD corrections play an important role in the reproduction of data at high transverse momenta in the energy range 20 GeV $ \leq \sqrt{s} \leq 200$ GeV. Recent calculations of photon and pion production in $pp$ collisions yield detailed information on the next-to-leading order contributions. However, the application of these results in proton-nucleus and nucleus-nucleus collisions is not straightforward. The study of nuclear effects requires a simplified understanding of the output of these computations. Here we summarize our analysis of recent calculations, aimed at handling the …
Entropy, dimensions and other multifractal characteristics of multiplicity distributions of relativistic charged hadrons produced in ion-ion collisions at SPS energies are investigated. The analysis of the experimental data is carried out in terms of phase space bin-size dependence of multiplicity distributions following the Takagi's approach. Yet another method is also followed to study the multifractality which, is not related to the bin-width and (or) the detector resolution, rather involves multiplicity distribution of charged particles in full phase space in terms of information entropy a…
In the past the analyses of inelastic p+p collision for example in terms of the hadron gas model have assumed that always both protons participate in the interaction. In this article we show that (at sqrt(s) = 17.3 GeV ) on average only 1,89 protons are interacting. Measurements of the mean multiplicities of protons, neutrons, charged pions, charged kaons and Λ hyperons allow to compute the number of initial state nucleons using conservation of baryon number, strangeness, and isospin. We further argue that once the number of initial state nucleons is given and the mean multiplicities of proton…
The strong suppression of the $J/ψ$ is studied in the framework of hadronic and quark gluon plasma models. Predictions for RHIC energies are presented.
A mean-field potential version of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to investigate the production of strange baryons, especially the $Λ$s and $\overlineΛ$s, from heavy ion collisions at SPS energies. It is found that, with the consideration of both formed and pre-formed hadron potentials in UrQMD, the transverse mass and longitudinal rapidity distributions of experimental data of both $Λ$s and $\overlineΛ$s can be quantitatively explained fairly well. Our investigation also shows that both the production mechanism and the rescattering process of hadrons pl…
Charmonium production and suppression in In+In and Pb+Pb reactions at SPS energies is investigated with the HSD transport approach within the 'hadronic comover model' as well as the 'QGP threshold scenario'. The results of the transport calculations for J/Psi suppression and the Psi prime to J/Psi ratio are compared with the recent data of the NA50 and NA60 Collaborations. We find that the comover absorption model - with a single parameter |M_0|^2 for the matrix element squared for charmonium-meson dissociation - performs best with respect to all data sets. The 'threshold scenario' - within di…
We present our calculation of electromagnetic effects, induced by the spectator charge on Feynman-$x_F$ distributions of charged pions in peripheral $Pb+Pb$ collisions at CERN SPS energies, including realistic initial space-time-momentum conditions for pion emission. The calculation is performed in the framework of a specific implementation of the fire-streak model, adopted to the production of both $π^-$ and $π^+$ mesons. Isospin effects are included to take into account the asymmetry in production of $π^+$ and $π^-$ at high rapidity. A comparison to a simplified model from the literature is …
Charmonium production in p+A collisions at SPS and FAIR energies
GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI亥姆霍兹重离子研究中心）；Institute for Theoretical Physics, Johann Wolfgang Goethe Universität（约翰·沃尔夫冈·歌德大学理论物理研究所）；Helmholtz Research Academy Hessen for FAIR (HFHF)（黑森FAIR亥姆霍兹研究学院）；SUBATECH UMR 6457 (IMT Atlantique, Université de Nantes, IN2P3/CNRS)（SUBATECH UMR 6457（大西洋高等矿业学院、南特大学、IN2P3/CNRS））；Frankfurt Institute for Advanced Studies（法兰克福高等研究院）
We construct a simple model of heavy ion collisions, local in the impact parameter plane, and appropriate for the SPS energy range. This model can be regarded as a new realization of the "fire-streak" approach, originally applied to studies of lower energy nucleus-nucleus reactions. Starting from local energy and momentum conservation, we nicely describe the broadening of the pion rapidity distribution when going from central to peripheral Pb+Pb collisions at $\sqrt{s_{NN}}$=17.3 GeV. The results of our calculations are compared with SPS experimental data. We discuss the resulting implications…
High energy photon emission rate from matter created in Pb + Pb collisions at CERN SPS energies is evaluated. The evolution of matter from the initial state up to freeze-out has been treated within the framework of (3+1) dimensional hydrodynamic expansion. We observe that the photon spectra measured by the WA98 experiment are well reproduced with hard QCD photons and photons from a thermal source with initial temperature ~ 200 MeV. The effects of the spectral changes of hadrons with temperature on the photon emission rate and on the equation of state are studied. Photon yield for Au + Au colli…
The production of charmonia is investigated for heavy-ion collisions from SPS to RHIC energies. Our approach incorporates two sources of $J/Ψ$ yield: (i) a direct contribution arising from early (hard) parton-parton collisions, subject to subsequent nuclear absorption, quark-gluon plasma and hadronic dissociation, and (ii) statistical production at the hadronization transition by coalescence of $c$ and $\bar{c}$ quarks. Within an expanding thermal fireball framework, the model reproduces $J/Ψ$ centrality dependencies observed at the SPS in Pb-Pb and S-U collisions reasonably well. The study of…
Studies of the ultrarelativistic collisions of hadrons and nuclei at different centrality and energy enable to explore the QCD phase diagram in a wide range of temperature and baryon density. Long-range correlation studies are considered as a tool, sensitive to the observation of phase transition and the critical point. In the present work, a Monte Carlo model of proton-proton, proton-nucleus, and nucleus-nucleus collisions is applied to heavy and light ion collisions at the cms energy range from a few up to several hundred GeV per nucleon. The model describes the nuclear collisions at the par…
Long range correlations are searched for by analyzing the experimental data on 16O-AgBr and 32S-AgBr collisions at 200A GeV/c and the results are compared with the predictions of a multi phase transport (AMPT) model. The findings reveal that the observed forward-backward (F-B) multiplicity correlations are mainly of short-range in nature. The range of F-B correlations are observed to extend with increasing projectile mass. The observed extended range of F-B correlations might be due to overall multiplicity fluctuations arising because of nuclear geometry. The findings are not sufficient for ma…
Single photon spectra in heavy-ion collisions at SPS energies are studied in the relativistic transport model that incorporates self-consistently the change of hadron masses in dense matter. We separate the total photon spectrum into `background' arising from the radiative decays of $π^0$ and $η$ mesons, and the `themal' one from other sources. For the latter we include contributions from radiative decays of $ρ$, $ω$, $η'$, and $a_1$, radiative decays of baryon resonances, as well as two-body processes such as $ππ\to ργ$ and $πρ\to πγ$. It is found that more than 95% of all photons come from t…
High-$p_T$ particle spectra in $p+p$ ($\bar p + p$), $p+A$ and $A+B$ collisions are calculated within a QCD parton model in which intrinsic transverse momentum, its broadening due to initial multiple parton scattering, and jet quenching due to parton energy loss inside a dense medium are included phenomenologically. The intrinsic $k_T$ and its broadening in $p+A$ and $A+B$ collisions due to initial multiple parton scattering are found to be very important at low energies ($\sqrt{s}<50$ GeV). Comparisons with $S+S$, $S+Au$ and $Pb+Pb$ data with different centrality cuts show that the differenti…
The particle ratios $k^+/π^+$, $π^-/K^-$, $\bar{p}/π^-$, $Λ/π^-$, $Ω/π^-$, $p/π^+$, $π^-/π^+$, $K^-/K^+$, $\bar{p}/p$, $\barΛ/Λ$, $\barΣ/Σ$, $ \barΩ/Ω$ measured at AGS, SPS and RHIC energies are compared with large statistical ensembles of $100,000$ events deduced from the CRMC EPOS $1.99$ and the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) hybrid model. In the UrQMD hybrid model two types of phase transitions are taken into account. All these are then confronted to the Hadron Resonance Gas Model. The two types of phase transitions are apparently indistinguishable. Apart from $k^+/π^…
We study e+e- pair production in proton-proton and in nucleus-nucleus collisions from SIS to LHC energies within the parton-hadron-string dynamics (PHSD) approach which incorporates explicit partonic degrees-of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We find a visible in-medium effect in the low mass dilepton sector from dynamical vector-meson spectral functions from SIS to SPS energies whereas at RHIC and LHC…
GSI Helmholtzzentrum für Schwerionenforschung GmbH（GSI亥姆霍兹重离子研究中心）；Institute for Theoretical Physics, Johann Wolfgang Goethe Universität, Frankfurt am Main, Germany（法兰克福歌德大学理论物理研究所）；Helmholtz Research Academy Hessen for FAIR (HFHF)（黑森亥姆霍兹FAIR研究院）；SUBATECH UMR 6457 (IMT Atlantique, Université de Nantes, IN2P3/CNRS)（南特大学/大西洋高等矿业学院/法国国家科学研究中心IN2P3 SUBATECH联合实验室）；Frankfurt Institute for Advanced Studies（法兰克福高级研究所）
We present results for final state charged particle (pseudo-)rapidity distributions in $\rm{p}$ + $\bar{\rm{p}}$ / $\rm{p}$ + $\rm{p}$ and Pb+Pb/Au+Au at ultra high energies (17.3 GeV $\leq$ $\sqrt{s_{\rm{NN}}}$ $\leq$ 14 TeV) from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD-v2.3) model. In addition, excitation functions of produced charged particle multiplicities ($N_{\rm{ch}}$) and pseudorapidity spectra are investigated up to LHC energies. Good agreement is observed between UrQMD and measured pseudorapidity distributions of charged particles up to the highest Tevatron and Sp$\b…
A unique parametrization of secondary (thermal) dilepton yields in heavy-ion experiments at CERN-SPS is proposed. This parametrization resembles a thermal $q \bar q$ annihilation rate. This is inspired by the observation that lepton pair production rates are quantitatively similar, whether expressed in a hadronic or partonic basis. Adding the thermal yield and the background contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 and HELIOS/3 data from experiments with lead and sulfur beams can be well describ…
Rho meson propagation in hot hadronic matter is studied in a model with coupling to $ππ$ states. Medium modifications are induced by a change of the pion dispersion relation through collisions with nucleons and $Δ's$ in the fireball. Maintaining gauge invariance dilepton production is calculated and compared to the recent data of the CERES collaboration in central S+Au collisions at 200 GeV/u. The observed enhancement of the rate below the rho meson mass can be largely accounted for.
The elliptic flow excitation function calculated in a full (3+1)d hybrid Boltzmann approach with an intermediate hydrodynamic stage for heavy ion reactions from GSI-SIS to the highest CERN-SPS energies is discussed in the context of the experimental data. In this study, we employ a hadron gas equation of state to investigate the differences in the dynamics and viscosity effects. The specific event-by-event setup with initial conditions and freeze-out from a non-equilibrium transport model allows for a direct comparison between ideal fluid dynamics and transport simulations. At higher SPS energ…
We study the enhancement of $c \bar c$ pair production that takes place in central heavy ion collisions due to the formation of clusters of strings. These clusters produce heavy flavors more efficiently due to their higher color. We discuss the competition between this mechanism and the well-known screening of color charge, which, above a critical string density, reduces strongly the probability of binding these $c \bar c$ pairs to form $J/Ψ$ particles. The dependence of $J/Ψ$ suppression on the centrality shows a peak at both RHIC and LHC energies corresponding to the percolation critical den…
We present a nonperturbative dynamical study of $e^+e^-$ production in proton- nucleus and nucleus-nucleus collisions at SPS energies on the basis of a covariant transport approach. For p + A reactions the dilepton yield for invariant masses m $\leq $ 1.2 GeV is found to be dominated by the decays of the $η, ρ, ω$ and $Φ$ mesons in line with the findings of the CERES collaboration. For S + Au collisions at 200 GeV/A the dilepton yield is, however, dominated by $π^+π^-$ annihilation due to the high pion densities achieved. Whereas for `free' meson masses and form factors the experimental cross …
The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding systems of heavy nuclei at 160 AGeV/$c$ are analyzed within the microscopic Quark Gluon String Model (QGSM). We found that even for the most heavy systems particle emission takes place from the whole space-time domain available for the system evolution, but not from the thin ''freeze-out hypersurface", adopted in fluid dynamical models. Pions are continuously emitted from the whole volume of the reaction and reflect the main trends of the system evolution. Nucleons in Pb+Pb collisions initially come from the surface regio…
The results of numerical calculating the total Mott-Bloch correction to the Bethe stopping formula and the Lindhard-Sorensen correction in the point nucleus approximation, as well as the Mott correction and the difference between the Lindhard-Sorensen and Bloch corrections, which were obtained by some rigorous and approximate methods, are compared for the ranges of a gamma factor of approximately from 1 to 10 and the ion nuclear charge number Z from 6 to 114. It is shown that the accurate calculation of the Mott-Bloch corrections based on the Mott exact cross section using a method previously …
A new striking feature of hadron production in nuclear collisions is the large stopping of the participating nucleons in hadron-nucleus and nucleus-nucleus collisions. This enhanced baryon stopping can be understood introducing new diquark breaking mechanisms in multistring models of hadron production. Here we show, that similar diquark breaking mechanisms occur at high energy even in hadron-hadron collisions. This effect leads to significant changes in the extrapolation of these models to Cosmic Ray energies.
Strangeness and baryon enhancement in heavy ion collisions are discussed in the framework of the String Fusion Model. The Monte Carlo version of this model is shown to reasonably reproduce three of the features that have been pointed out as evidences of the finding of the Quark Gluon Plasma. Namely hyperon/antihyperon enhancement, dependence of the slope of the $p_{T}$ distributions on the mass of the produced particles and on the centrality of the collision, are described. Predictions for RHIC and LHC energies are presented.
After 15 years of heavy-ion collision experiments at the AGS and SPS, the recent turn-on of RHIC has initiated a new stage of quark-gluon plasma studies. I review the evidence for deconfined quark-gluon matter at SPS energies and the recent confirmation of some of the key ideas by the new RHIC data. Measurements of the elliptic flow at RHIC provide strong evidence for efficient thermalization during the very early partonic collision stage, resulting in a well-developed quark-gluon plasma with almost ideal fluid-dynamical collective behaviour and a lifetime of several fm/c.
Probing Forward-Backward Multiplicity Correlations and Fluctuations Using the Strongly Intensive Observable $Σ$ in Pb-Pb Collisions at SPS Energies with UrQMD
Variable Energy Cyclotron Centre（可变能量回旋加速器中心）；GSI Helmholtzzentrum für Schwerionenforschung GmbH (GSI)（GSI亥姆霍兹重离子研究中心有限公司）
Coarse-grained output from transport calculations is used to determine thermal dilepton emission rates by applying medium-modified spectral functions from thermal quantum field theoretical models. By averaging over an ensemble of events generated with the UrQMD transport model, we extract the local thermodynamic properties at each time step of the calculation. With an equation of state the temperature $T$ and chemical potential $μ_{\mathrm{B}}$ can be determined. The approach goes beyond simplified fireball models of the bulk-medium evolution by treating the full (3+1)-dimensional expansion of…
We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the earlier developed and recently refined parton-cascade/cluster-hadronization model and its Monte Carlo implementation. This space-time model involves the dynamical interplay of perturbative QCD parton production and evolution, with non-perturbative parton-cluster formation and hadron production through cluster decays. Using computer simulations, we are able to follow the entwined time-evolution of parton and hadron degrees of freedom in both position and momentum space, from the instant of nuclear overlap to the final yi…
Event-by-event (ebe) fluctuations in mean pseudorapidity values of relativistic charged particles in full phase space is studied by analysing experimental data on $^{16}O-AgBr$ collisions at 14.5A, 60A, and 200A GeV/c and $^{32}S-AgBr$ collisions at 200A GeV/c. The findings are compared with the prediction of A Multi-Phase Transport(\amm) model and those obtained from the analysis of correlation free Monte-Carlo events. Fluctuations in mean pseudorapidity distributions are noticed to be in excess to that expected from the statistically independent particle emission. The observed dependence of …
We use quasiparticle description of deconfined matter in nuclear collisions at finite temperature and chemical potential. We assume that evolution of expanding system is isentropic. Using theoretical formulas and experimental meaning for the average multiplicity of charged and neutral particles and also of net nucleons ($N-\bar{N}$) per unit central rapidity, we calculate the initial temperature $T_0$, and the volume $V_0$ for the collisions of heavy nuclei ($Pb+Pb$ and $Au+Au$) at SPS and RHIC energies. At calculations we use the conservation of entropy and of number net nucleons in initial p…
We present a Monte-Carlo simulation of energy deposition process in relativistic heavy-ion collisions based on a new realization of the Interacting-Gluon-Model (IGM) for high energy $N-N$ collisions. In particular we show results for proton spectra from collisions of $E_{lab}=200 \ GeV/N$ $^{32}$S beam incident on $^{32}$S target and analyze the energy and mass dependence of nuclear stopping power predicted by our model. Theoretical predictions for proton rapidity distributions of both $^{208}$Pb + $^{208}$Pb collisions at $E_{lab}=160 \ GeV/N$ CERN SPS and $^{197}$Au + $^{197}$Au at $\sqrt{s_…
The quark combination mechanism of hadron production is applied to nucleus-nucleus collisions at the CERN Super Proton Synchrotron (SPS) and BNL Alternating Gradient Synchrotron (AGS). The rapidity spectra of identified hadrons and their spectrum widths are studied. The data of $π^{-}$, $K^{\pm}$, $ϕ$, $Λ$, $\barΛ$, $Ξ^{-}$, and $\barΞ^{+}$ at 80 and 40 AGeV, in particular at 30 and 20 AGeV where the onset of deconfinement is suggested to happen, are consistently described by the quark combination model. However at AGS 11.6 AGeV below the onset the spectra of $π^{\pm}$, $K^{\pm}$ and $Λ$ can n…
Experimental data on the onset of a so-called anomalous J/psi suppression in PbPb collisions at the SPS are considered in the framework of string percolation model. This onset is observed at a certain collision centrality, characterized by the number of nucleons-participants (Npart) related to the impact-parameter. Modified Bjorken formula calculations are performed for the local energy densities in AA collisions at different impact-parameters and with detailed account of the latest data available on the charged particles densities at midrapidity. Finally we compare variations of mean local en…
We suggest to use net-baryon rapidity distributions in central relativistic heavy-ion collisions at SPS, RHIC and LHC energies in order to probe saturation physics. Within the color glass condensate framework based on small-coupling QCD, net-baryon rapidity distributions are shown to exhibit geometric scaling. In a comparison with RHIC data in Au + Au collisions at sqrt(s_NN) = 62.4 GeV and 200 GeV the gradual approach to the gluon saturation regime is investigated. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb + Pb collisions at LHC energies of sqrt (s_N…
