Collective flow observables are known to be a sensitive tool to gain insights on the equation of state of nuclear matter from heavy-ion collision observations. Towards more quantitative constraints one has to carefully assess other influences on the collective behaviour. In this work a hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) is applied to study the first four anisotropic flow coefficients in Au+Au collisions at $E_{\rm lab}=1.23A$ GeV in the context of the recently measured data by the HADES collaboration. In particular, the formation of light nuclei is important in this energy regime. Two different approaches are contrasted to each other: A clustering algorithm inspired by coalescence as well as microscopic formation of deuterons via explicit cross-sections. The sensitivity of directed and elliptic flow observables to the strength of the Skyrme mean field is explored. In addition, it is demonstrated that the rapidity-odd $v_3$ coefficient is practically zero in this energy regime and the ratio of $v_4/v_2^2$ is close to the value of 0.5 expected from hydrodynamic behaviour. This study establishes the current understanding of collective behaviour within the SMASH approach and lays the ground for future more quantitative constraints on the equation of state of nuclear matter within improved mean field calculations.
We study systematically the production of strangeness in nuclear reactions from SIS to SPS energies within the covariant hadronic transport approach HSD. Whereas the proton and pion rapidity distributions as well as pion transverse momentum spectra are well described in the hadronic transport model from 2-200 AGeV, the $K^+$ and $K^-$ spectra are noticeably underestimated at AGS energies while the $K^+$ spectra match well at SIS and SPS energies with the experimental data. We conclude that the failure of the hadronic model at AGS energies points towards a nonhadronic phase during the collision…
The properties of strange pseudoscalar and vectors mesons as well as strange baryon resonances in dense matter are reviewed. Some open questions on the properties of strange hadrons in medium are addressed, such as the experimental signatures of in-medium effects coming from the hadronic phase on the final observables in heavy-ion collisions for the experimental conditions at SIS, RHIC and LHC energies.
We calculate $p, π^\pm, K^\pm$ and $Λ$(+$Σ^0$) rapidity distributions and compare to experimental data from SIS to SPS energies within the UrQMD and HSD transport approaches that are both based on string, quark, diquark ($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom. The two transport models do not include any explicit phase transition to a quark-gluon plasma (QGP). It is found that both approaches agree rather well with each other and with the experimental rapidity distributions for protons, $Λ$'s, $π^\pm$ and $K^\pm$. Inspite of this apparent agreement both transport mode…
Production of strange hadrons in elementary and heavy-ion reactions is studied with the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). The poorly known branching ratios of the relevant hadronic resonances are constrained from the known elementary hadronic cross sections and from invariant mass spectra of dileptons. The constrained model is employed as a baseline to compare to heavy-ion-collision experiments at low energies ($E_\text{kin} = 1-2A\,\text{GeV}$) and to predict some of the upcoming pion-beam results by HADES, which are expected to be s…
We calculate excitation functions for various dynamical quantities as well as experimental observables from SIS to RHIC energies within the HSD transport approach which is based on string, quark, diquark ($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom without including any explicit phase transition to a quark-gluon plasma (QGP). It is argued that the failure of this more 'conventional' approach in comparison to experimental data should indicate the presence of a different phase which might be either attributed to space-time regions of vanishing scalar quark condensate ($<q\b…
The properties of $K^+$ and $K^-$ mesons are studied in nuclear reactions from SIS to RHIC energies within the covariant transport approach HSD in comparison to the experimental data whenever available. Whereas kaon abundancies and spectra indicate little repulsive or vanishing selfenergies in the medium, antikaons are found to experience strong attractive potentials in nucleus-nucleus collisions at SIS energies. However, even when including these potentials the $K^+$ and $K^-$ spectra at AGS energies are noticeably underestimated showing an experimental excess of strangeness that points towar…
We analyze the baryon sideward and elliptic flow from SIS (0.25 $\sim$ 2 A GeV) to AGS (2 $\sim 11.0A$GeV) energies for Au + Au collisions in the relativistic transport model RBUU that includes all baryon resonances up to a mass of 2 GeV as well as string degrees of freedom for the higher mass continuum. There are two factors which dominantly determine the baryon flow at these energies: the momentum dependence of the scalar and vector potentials and the resonance-string degrees of freedom. We fix the explicit momentum dependence of the nucleon-meson couplings within the NL3 parameter set by th…
We study the propagation of non-strange and strange meson modes in hadronic matter considering both isospin and strangeness mixings induced by quantum fluctuations in the medium. Baryons are described using the Quark Meson Coupling model extended to include interactions of strange quarks. In particular we evaluate the dependence of the meson masses on the baryonic density, the strangeness fraction and the isospin asymmetry of the medium. We have found a considerable admixture of strangeness and isospin in the sigma-mode in the high density regime.
Production of the doubly strange $Ξ$ baryon in heavy-ion collisions at \textrm{SIS} energies is studied in a relativistic transport model that includes perturbatively the strangeness-exchange reactions $\bar{K}Λ\to πΞ$ and $\bar{K}Σ\to πΞ$. Taking the cross sections for these reactions from the predictions of a hadronic model, we find that the $Ξ$ yield is about $10^{-4}$ in central collisions of $% ^{58}$Ni + $^{58}$Ni at $E/A=1.93$ \textrm{GeV}. The $Ξ$ yield is further found to be more sensitive to the magnitude of the cross sections for strangeness-exchange reactions than to the medium eff…
Utilizing a coarse-graining method to convert hadronic transport simulations of Au+Au collisions at SIS energies into local temperature, baryon and pion densities, we compute the pertinent radiation of thermal dileptons based on an in-medium $ρ$ spectral function that describes available spectra at ultrarelativistic collision energies. In particular, we analyze how far the resulting yields and slopes of the invariant-mass spectra can probe the lifetime and temperatures of the fireball. We find that dilepton radiation sets in after the initial overlap phase of the colliding nuclei of about 7 fm…
The behavior of hadronic matter at high baryon densities is studied within Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is observed for Au+Au collisions from SIS up to SPS energies. The excitation function of flow shows strong sensitivities to the underlying equation of state (EOS), allowing for systematic studies of the EOS. Dilepton spectra are calculated with and without shifting the $ρ$ pole. Except for S+Au collisions our calculations reproduce the CERES data.
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…
Attention is drawn to the role played by the size of the system in the thermodynamic analysis of particle yields in relativistic heavy ion collisions at SIS energies. This manifests itself in the non-linear dependence of K+ and K- yields in $AA$ collisions at 1 -- 2 A.GeV on the number of participants. It is shown that this dependence can be quantitatively well described in terms of a thermal model with a canonical strangeness conservation. The measured particle multiplicity ratios (pi+/p, pi-/pi+, d/p, K+/pi+ and K+/K- but not eta/pi0) in central Au-Au and Ni-Ni collisions at 0.8 -- 2.0 A.GeV…
We consider a spherical volume of hot and dense hadronic matter (fireball) expanding into a vacuum. It is assumed that initially the fireball matter is in local thermal and chemical equilibrium with vanishing collective velocity. The time evolution of the fireball is studied in parallel within the GiBUU transport model and an ideal hydrodynamic model. The equation of state of an ideal hadronic gas is used in the hydrodynamic calculation. The same set of hadronic species is used in transport and fluid-dynamical simulations. Initial coordinates and momenta of hadrons in transport simulations hav…
The regeneration of hadronic resonances is discussed for heavy ion collisions at SPS and SIS-300 energies. The time evolutions of Delta, rho and phi resonances are investigated. Special emphasize is put on resonance regeneration after chemical freeze-out. The emission time spectra of experimentally detectable resonances are explored.
We give a reminder on the major inputs of microscopic hadronic transport models and on the physics aims when describing various aspects of relativistic heavy ion collisions at SPS energies. We then first stress that the situation of particle ratios being reproduced by a statistical description does not necessarily mean a clear hint for the existence of a fully isotropic momentum distribution at hadrochemical freeze-out. Second, a short discussion on the status of strangeness production is given. Third we demonstrate the importance of a new collective mechanism for producing (strange) antibaryo…
Dilepton invariant-mass spectra for heavy-ion collisions at SIS 18 and BEVALAC energies are calculated using a coarse-grained time evolution from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. The coarse-graining of the microscopic simulations enables to calculate thermal dilepton emission rates by application of in-medium spectral functions from equilibrium quantum-field theoretical calculations. The results show that extremely high baryon chemical potentials dominate the evolution of the created hot and dense fireball. Consequently, a significant modification of the $ρ$ spe…
Collective flow of Lambda hyperons in heavy ion reactions at SIS energies is investigated. It is found that a $Λ$ mean field constructed on the basis of the quark model leads to a good description of the experimental data of the in-plane transverse flow of $Λ$'s. The attractive mean field can also give rise to an additional "virtual" $Λ$ radial flow directed inwards, which is reflected by a "concave" structure of the transverse mass spectrum of the $Λ$ hyperons emitted at midrapidity. The $Λ$ radial flow is found to exhibit a strong mass dependence: The flow is visible in the Ni+Ni system, but…
The properties of $π, η, K^+$ and $K^-$ mesons are studied in nuclear reactions from SIS to SPS energies within the covariant transport approach HSD in comparison to the experimental data. Whereas the pion, $η$ and kaon abundancies and spectra indicate little or vanishing selfe-nergies for these mesons in the medium, antikaons (as well as antiprotons) are found to experience strong attractive potentials in nucleus-nucleus collisions at SIS energies. However, even when including these potentials the $K^+$ and $K^-$ spectra at AGS energies are noticeably underestimated showing an experimental ex…
The Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, a microscopic transport model, is used to study the directed and elliptic collective flows and the nuclear stopping in Au+Au collisions at incident energies covered by INDRA and lower-energy FOPI experiments. It is seen clearly that these observables are sensitive to both, the potential terms (including iso-scalar and iso-vector parts as well as the momentum dependent term) in the equation of state (EoS) and the collision term (including the Pauli-blocking and the medium-modified nucleon-nucleon elastic cross section (NNECS)). The…
The phenomenon of collective flow in relativistic heavy ion collisions is studied using the hadronic cascade model ARC. Direct comparison is made to data gathered at the Bevalac, for Au+Au at $p=1-2$ GeV/c. In contrast to the standard lore about the cascade model, collective flow is well described quantitatively without the need for explicit mean field terms to simulate the nuclear equation of state. Pion collective flow is in the opposite direction to nucleon flow as is that of anti-nucleons and other produced particles. Pion and nucleon flow are predicted at AGS energies also, where, in ligh…
I give an overview of the latest development in understanding collective phenomena in high-multiplicity hadronic final state from relativistic nucleus-nucleus, proton-nucleus and proton-proton collisions. Upon reviewing the experimental data and confronting them with theoretical models, a unified paradigm in describing the observed collectivity across all hadronic collision systems is emerging. Potential future paths toward addressing key open questions, especially on collectivity in small systems (pp, pA), are discussed.
A critical discussion of the present status of the CERN experiments on charm dynamics and hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A$\cdot$GeV: here the hydrodynamic model has predicted the collapse of the $v_1$-flow and of the $v_2$-flow at $\sim 10$ A$\cdot$GeV; at 40 A$\cdot$GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as potential evidence for a first order phase transition at high baryon dens…
The proper description of hadronic decays of baryon resonances has been a long standing problem in soliton models for baryons. In this talk I present a solution to this problem in the three flavor Skyrme model that is consistent with large-Nc consistency conditions. As an application I discuss hadronic pentaquark decays and show that predictions based on axial current matrix elements are erroneous.
This work investigates the collective motion of kaons in heavy ion reactions at SIS energies (about 1-2 GeV/nucleon). A radial collective flow of $K^+$ mesons is predicted to exist in central Au + Au collisions, which manifests in a characteristic "shoulder-arm" shape of the transverse mass spectrum of the midrapidity $K^+$ mesons. The $K^+$ radial flow arises from the repulsive $K^+$ mean field in nuclear matter. In spite of a strong reabsorption and rescattering the attractive $K^-$ mean field leads as well to a collective radial flow of $K^-$ mesons. The $K^-$ radial flow, however, is diffe…
Collective interactions in the preequilibrium quark matter and hadronic resonance gas stage of ultrarelativistic nucleus-nucleus collisions are studied in the framework of the the transport theoretical approach RQMD. The paper reviews string fusion into color ropes and hadronic rescattering which serve as models for these interactions. Hadron production in central Pb(160AGeV) on Pb collisions has been calculated. The changes of the final flavor composition are more pronounced than in previous RQMD studies of light ion induced reactions at 200AGeV. The ratio of created quark pairs $s\bar{s}$/($…
We study the collective flow of open charm mesons and charmonia in Au+Au collisions at $\sqrt{s}$ = 200 GeV within the hadron-string-dynamics (HSD) transport approach. The detailed studies show that the coupling of $D,\bar{D}$ mesons to the light hadrons leads to comparable directed and elliptic flow as for the light mesons. This also holds approximately for $J/Ψ$ mesons since more than 50% of the final charmonia for central and mid-central collisions stem from $D+\bar{D}$ induced reactions in the transport calculations. The transverse momentum spectra of $D,\bar{D}$ mesons and $J/Ψ$'s are onl…
The change of hadron properties in dense matter based on various theoretical approaches are reviewed. Incorporating these medium effects in the relativistic transport model, which treats consistently the change of hadron masses and energies in dense matter via the scalar and vector fields, heavy-ion collisions at energies available from SIS/GSI, AGS/BNL, and SPS/CERN are studied. This model is seen to provide satisfactory explanations for the observed enhancement of kaon, antikaon, and antiproton yields as well as soft pions in the transverse direction from the SIS experiments. In the AGS heav…
The behavior of hadronic matter at high baryon densities is studied within Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is observed for Au+Au collisions from SIS up to SPS energies. The excitation function of flow shows strong sensitivities to the underlying equation of state (EOS), allowing for systematic studies of the EOS. Effects of a density dependent pole of the $ρ$-meson propagator on dilepton spectra are studied for different systems and centralities at CERN energies.
Using the Ultra-relativistic Quantum Molecular Dynamics ({\tt UrQMD}) model, we investigate the azimuthal correlations in p--Pb collisions at $\sqrt{s_{_{\rm NN}}}=5.02$ TeV. It is shown that the simulated hadronic p--Pb system can not generate the collective flow signatures, but mainly behaves as a non-flow dominant system. However, the characteristic $v_{2}(p_{\rm T})$ mass-ordering of pions, kaons and protons is observed in {\tt UrQMD} simulations, which is the consequence of hadronic interactions and not necessarily associated with strong fluid-like expansions.
The properties of $K$ and $\bar K$ mesons in nuclear matter at finite temperature are obtained from a chiral unitary approach in coupled channels which incorporates the $s$- and p-waves of the kaon-nucleon interaction. The in-medium solution accounts for Pauli blocking effects, mean-field binding on all the baryons involved, and $π$ and kaon self-energies. The $\bar K$ spectral function spreads over a wide range of energies, reflecting the melting of the $Λ(1405)$ resonance and the contribution of hyperon-hole components at finite temperature. In the $KN$ sector, the quasi-particle peak is con…
Collective behaviour has been observed in hadronic measurements of high multiplicity proton+lead collisions at the Large Hadron Collider (LHC), as well as in (proton, deuteron, helium-3)+gold collisions at the Relativistic Heavy-Ion Collider (RHIC). To better understand the evolution dynamics and the properties of the matter created in these small systems, a systematic study of the soft hadronic observables together with electromagnetic radiation from these collisions is performed, using a hydrodynamic framework. Quantitative agreement is found between theoretical calculations and existing exp…
We review the results from the various hydrodynamical and transport models on the collective flow observables from AGS to RHIC energies. A critical discussion of the present status of the CERN experiments on hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A$\cdot$GeV: here the hydrodynamic model has predicted the collapse of the $v_1$-flow and of the $v_2$-flow at $\sim 10$ A$\cdot$GeV; at 40 A$\cdot$GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at …
We present a microscopic model for collective effects in high multiplicity proton--proton collisions, where multiple partonic subcollisions give rise to a dense system of strings. From lattice calculations we know that QCD strings are transversely extended, and we argue that this should result in a transverse pressure and expansion, similar to the flow in a deconfined plasma. The model is implemented in the PYTHIA8 Monte Carlo event generator, and we find that it can qualitatively reproduce the long range azimuthal correlations forming a near-side ridge in high multiplicity proton--proton even…
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…
We investigate the interplay between hydrodynamic fluctuations and initial longitudinal fluctuations for their effects on the rapidity decorrelation of collective flow in high-energy nuclear collisions. We use a (3+1)-dimensional integrated dynamical model in which we combine initial conditions with longitudinal fluctuations, fluctuating hydrodynamics and hadronic cascades. We analyse the factorisation ratio in the longitudinal direction to study the effect of these fluctuations on the rapidity decorrelation. We find an essential difference between the effects of the hydrodynamic fluctuations …
The influence of the chiral mean field on the collective motion of kaons in relativistic heavy ion reactions at SIS energies is investigated. We consider three types of collective motion, i.e. the transverse flow, the out-of-plane flow (squeeze-out) and the radial flow. The kaon dynamics is thereby described with a relativistic mean field as it originates form chiral lagrangiens. For the $K$ mesons inside the nuclear medium we adopt a covariant quasi-particle picture including scalar and vector fields and compare this to a treatment with a static potential like force. The comparison to the ava…
We investigated the strange hadrons transverse momentum ($p_T$) spectra in Au-Au collision at $\sqrt {s_{NN}}$ = 54.4 GeV in the framework of modified Hagedorn function with embedded flow. We extracted the kinetic freeze-out temperature $T_0$, transverse flow velocity $β_T$, kinetic freeze-out volume $V$, mean transverse momentum $<p_T>$, the entropy parameter $n$ and the multiplicity parameter $N_0$. We reported that all these parameters increase towards the central collisions. The larger kinetic freeze-out temperature , transverse flow velocity, kinetic freeze-out volume and the entropy para…
Using the EPOS3 model with UrQMD to describe the hadronic phase, we study the production of short-lived hadronic resonances and the modification of their yields and $p_{T}$ spectra in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. High-multiplicity p-Pb collisions exhibit similar behavior to mid-peripheral Pb-Pb collisions at LHC energies, and we find indications of a short-lived hadronic phase in p-Pb collisions that can modify resonance yields and $p_{T}$ spectra through scattering processes. The evolution of resonance production is investigated as a function of the system size, which is rel…
The azimuthal anisotropies of the collective transverse flow of charged hadrons are investigated in a wide range of heavy-ion collision energies within the microscopic Parton-Hadron-String Dynamics (PHSD) transport 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. The experimentally observed increase of the elliptic flow $v_2$ of charged hadrons with collision ene…
We introduce a combined macroscopic/microscopic transport approach employing relativistic hydrodynamics for the early, dense, deconfined stage of the reaction and a microscopic non-equilibrium model for the later hadronic stage where the equilibrium assumptions are not valid anymore. Within this approach we study the dynamics of hot, bulk QCD matter, which is expected to be created in ultra-relativistic heavy ion collisions at the SPS, the RHIC and the LHC. Our approach is capable of self-consistently calculating the freeze-out of the hadronic system, while accounting for the collective flow o…
We present the detail of a newly developed relativistic transport model (ART 1.0) for high energy heavy-ion collisions. Using this model, we first study the general collision dynamics between heavy ions at the AGS energies. We then show that in central collisions there exists a large volume of sufficiently long-lived superdense hadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition. The size and lifetime of this matter are found to depend strongly on the equation of state. We also investigate the degree and…
Collective effects in O-O and Ne-Ne collisions at $\sqrt{s_{\mathrm{NN}}}$=5.36 TeV from a hybrid approach
Goethe University Frankfurt（法兰克福歌德大学）；Frankfurt Institute for Advanced Studies（法兰克福高等研究院）；GSI Helmholtzzentrum für Schwerionenforschung（GSI亥姆霍兹重离子研究中心）；Helmholtz Research Academy Hesse for FAIR (HFHF)（黑森亥姆霍兹FAIR研究学院）
We update our calculations of thermal-photon production in nuclear collisions at the Relativistic Heavy-Ion Collider (RHIC). Specifically, we address the recent experimental observation of an elliptic flow of direct photons comparable in magnitude to that of pions, which is at variance with expectations based on quark-gluon plasma (QGP) dominated photon radiation. Our thermal emission rate is based on previous work, i.e., resummed leading-order QGP emission and in-medium hadronic rates in the confined phase. These rates are nearly degenerate at temperatures close to the expected QCD-phase chan…
Mini-jet production in ultra-relativistic nuclear collisions leads to initial conditions characterized by large fluctuations of the local energy density (hot spots) and of the collective flow field (turbulence). Assuming that local equilibrium is reached on a small time scale, $\sim 0.5$ fm/c, the transverse evolution of those initial conditions is computed using hydrodynamics. We find that a new class of collective flow phenomena (hadronic volcanoes) could arise under such conditions. This could be observable via enhanced azimuthal fluctuations of the transverse energy flow, $d^2E_\perp/dϕdy$…
Using the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, we investigate azimuthal correlations in p--Pb collisions at $\sqrt{s_{_{\rm NN}}}=5.02$ TeV. Comparison with the experimental data shows that UrQMD can not reproduce the multiplicity dependence of 2- and 4-particle cumulants, especially the transition from positive to negative values of $c_{2}\{4\}$ in high multiplicity events, which has been taken as experimental evidence of collectivity in p--Pb collisions. Meanwhile, UrQMD can not qualitatively describe the differential elliptic flow, $v_{2}(p_{\rm T})$, of all charged …
Probing the QCD Phase Structure with Dileptons from SIS to LHC Energies
Frankfurt Institute for Advanced Studies (FIAS)（法兰克福高等研究所）；Helmholtz Research Academy Hessen for FAIR (HFHF)（黑森亥姆霍兹FAIR研究院）；GSI Helmholtz Center for Heavy Ion Physics（重离子物理亥姆霍兹中心）；Institute for Theoretical Physics, Johann Wolfgang Goethe University（约翰·沃尔夫冈·歌德大学理论物理研究所）；GSI Helmholtzzentrum fur Schwerionenforschung GmbH（重离子研究亥姆霍兹中心有限公司）；State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）
We attempt to describe the rapidity and transverse momentum spectra of strange as well as non-strange hadrons e.g. cascade,cascadebar, lambda , lambdabar, proton, protonbar,(omega+omegabar, Kaon, anti-Kaon and their ratios in the ultra-relativistic collisions of gold nuclei at (Root sNN)=200 GeV. This is done by using a statistical thermal freeze-out model which incorporates the rapidity (collision) axis as well as transverse direction boosts developed within an expanding hot and dense hadronic fluid (fireball) till the final freeze-out. We determine the thermo-chemical freeze-out conditions p…
QCD strings originate from high-energy scattering in the form of Reggeons and Pomerons, and have been studied in some detail in lattice numerical simulations. Production of multiple strings, with their subsequent breaking, is now a mainstream model of high energy $pp$ and $pA$ collisions. Recent LHC experiments revealed that high multiplicity end of such collisions show interesting collective effects. This ignited an interest in the interaction of QCD strings and multi-string dynamics. Holographic models, collectively known as AdS/QCD, developed in the last decade, describe both hadronic spect…
Collective flow in collisions between Lead nuclei at LHC are influenced by random initial state fluctuations, especially for odd harmonics. Here we extend fluctuation studies to longitudinal fluctuations, which may have significant effect on the rapidity distribution of odd harmonics. Furthermore center of mass rapidity fluctuations are measurable, but not yet analysed. Here in the PACIAE parton and hadron molecular dynamics model we make an analysis of initial state fluctuations. As previous analyses discussed mainly the effects of fluctuations on eccentricity and the elliptic flow we pay par…
We study the dilepton production in heavy-ion collisions at energies of 1-2 AGeV as well as in proton induced pp, pn, pd and p+A reactions from 1 GeV up to 3.5 GeV. For the analysis we employ three different transport models - the microscopic off-shell Hadron-String-Dynamics (HSD) transport approach, the Isospin Quantum Molecular Dynamics (IQMD) approach as well as the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) approach. We confirm the experimentally observed enhancement of the dilepton yield (normalized to the multiplicity of neutral pions $N_{π^0}$) in heavy-ion collisions with re…
We review the collectivity and the suppression pattern of charmed mesons - produced in proton-nucleus and nucleus-nucleus collisions at SPS (158 AGeV) and RHIC energies (21 ATeV) - in comparison to dynamical and thermal models. In particular, we examine the charmonium `melting' and the `comover dissociation' scenarios - implemented in a microscopic transport approach - in comparison to the available data from the SPS and RHIC. The analysis shows that the dynamics of c, c-bar quarks at RHIC are dominated by partonic or `pre-hadronic' interactions in the strongly coupled plasma stage. Both the `…
In the first part I discuss the sensitivity of collective matter expansion in ultrarelativistic heavy-ion collisions to the transition between quark and hadronic matter (physics of the softest point of the Equation of State). A kink in the centrality dependence of elliptic flow has been suggested as a signature for the phase transition in hot QCD matter. Indeed, preliminary data of NA49 presented at this conference show first indications for the predicted kink. In the second part I have a look at the present theories of heavy-ion reactions. These remarks may also be seen as a critical comment …
The mass ordering of $v_{2}^{hadron}$ is regarded as one of the key signatures of collective behaviour in ultra relativistic heavy ion collisions. This observation has been found to be in compliance with the hydrodynamical response of a strongly interacting system to the initial spatial anisotropy. Flow co-efficients measured with identified particles in p-Pb/d-Au collisions have shown similar mass-splitting of $v_{2}^{hadron}$ indicating towards the presence of collective dynamics in small collision systems. Arguably, small size in the overlap geometry of such colliding systems may not be sui…
A blast-wave parametrization, including a full set of hadronic resonances, is used to model a small system, with total particle multiplicity comparable to the one measured in the high-multiplicity pp collisions at the LHC. Calculations are preformed for three cases: with negligible, regular and strong radial flow on the blast-wave hypersurface. We investigate the effects of flow on inclusive p_T spectra as well as on 1D and 3D femtoscopic radii for pions. Special emphasis is put on the role of pions from resonance decays. In particular we show that they magnify the flow effects present in the …
Within an isospin- and momentum-dependent hadronic transport model it is shown that the recent FOPI data on the $π^-/π^+$ ratio in central heavy-ion collisions at SIS/GSI energies (Willy Reisdorf {\it et al.}, NPA {\bf 781}, 459 (2007)) provide circumstantial evidence suggesting a rather soft nuclear symmetry energy \esym at $ρ\geq 2ρ_0$ compared to the Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and the need for further experimental confirmations are discussed.
Strange particles such as the kaon and lambda are useful in probing the properties of dense matter formed in heavy ion collisions. We review in this talk the theoretical understandings of their properties in nuclear medium based on both the effective chiral Lagrangian and the phenomenological hadronic model. We further review the effects due to changes in their in-medium properties on their collective flow in heavy ion collisions.
