We determine the decoupling surfaces for the hydrodynamic description of heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic expansion rate with the microscopic pion-pion scattering rate. The pion $p_T$ spectra for nuclear collisions at RHIC and LHC are computed by applying the Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with those obtained from the constant-temperature freeze-out surfaces. Comparison with RHIC data shows that the system indeed decouples when the expansion rate becomes comparable with the pion scattering rate. The dynamical decoupling based on the rates comparison also suggests that the effective decoupling temperature in central heavy ion collisions remains practically unchanged from RHIC to LHC.
The influence of the nuclear Coulomb field on transverse spectra of $π^+$ and $π^-$ 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 $π^-/π^+$ 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.
We analyze the hadronic freeze-out in ultra-relativistic heavy ion collisions at RHIC in a transport approach which combines hydrodynamics for the early, dense, deconfined stage of the reaction with a microscopic non-equilibrium model for the later hadronic stage at which the hydrodynamic equilibrium assumptions are not valid. With this ansatz we are able to self-consistently calculate the freeze-out of the system and determine space-time hypersurfaces for individual hadron species. The space-time domains of the freeze-out for several hadron species are found to be actually four-dimensional, a…
Medium effects which include color screening and Landau-Pomeranchuk-Migdal suppression of induced radiation are discussed in connection with the equilibration of dense partonic system in ultrarelativistic heavy ion collisions. Taking into account of these medium effects, the equilibration rate for a gluonic gas are derived and the consequences are discussed.
We present the first comparisons of experimental data with phenomenological results from 3+1d quasiparticle anisotropic hydrodynamics (aHydroQP). We compare charged-hadron multiplicity, identified-particle spectra, identified-particle average transverse momentum, charged-particle elliptic flow, and identified-particle elliptic flow produced in LHC 2.76 TeV Pb+Pb collisions. The dynamical equations used for the hydrodynamic stage utilize non-conformal aHydroQP. The resulting aHydroQP framework naturally includes both shear and bulk viscous effects in addition to higher-order non-linear transpor…
The role of minijet production as initial conditions for QGP production at $τ\sim 0.1 fm/c$ in nuclear collisions at the LHC and RHIC energies is discussed.
We calculate the centrality dependence of inclusive cross section of large-pT charmed-meson ($D^{0}$, $D^{*}$, $D^{*+}$, and $D_{s}^{+}$) from heavy quark fragmentation by the hard photoproduction processes for the nucleus-nucleus collisions in ultrarelativistic heavy ion collisions. The numerical results indicate that the modification of the hard photoproduction processes cannot be negligible for the charmed-meson production in Au-Au collisions at Relativistic Heavy Ion Collider (RHIC) and Pb-Pb collisions at Large Hadron Collider (LHC).
In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation …
In recent works [Segev,Wells; Baltz, McLerran; Eichmann, Reinhardt, Schramm, Greiner] it was claimed that the Coulomb correction to the $e^+e^-$ production cross section in relativistic heavy-ion collisions is absent. We point out that this statement is in obvious contradiction to some well known results. We obtain large Coulomb corrections in the pair production cross section for the RHIC and LHC heavy-ion colliders.
We review the production of lepton pairs during high energy nuclear collisions. We highlight the information being carried out of the hot and dense strongly interacting medium. We describe the phenomenon of scalar-vector mixing that can take place in a dense medium and suggest possible measurable signatures of this effect in high energy heavy ion collisions.
If the bulk viscosity of QCD matter is large, the effective pressure of the hot and dense matter created in ultrarelativistic heavy ion collisions can become negative, leading to instabilities in the evolution of the plasma. In the context of heavy ion collisions, this effect is sometimes referred to as cavitation. In this contribution we discuss the onset of cavitation in event-by-event hydrodynamic simulations of ultrarelativistic heavy ion collisions at LHC energies. We estimate how large the bulk viscosity of the QGP has to be in the QCD (pseudo) phase transition region in order for the ef…
Dilepton production associated with minijets is calculated in ultrarelativistic heavy ion collisions using the first order approximation of the dilepton fragmentation functions of quarks and gluons. The full QCD evolution of the fragmentation functions is also studied. We find that the dilepton pairs from the fragmentation of minijets are comparable to direct Drell-Yan at $\sqrt{s}=200$ AGeV for small dilepton invariant mass $M\sim$ 1-2 GeV/c$^2$ while dominant over a large range of mass at $\sqrt{s}=6400$ AGeV.
The effect of shadowing on the early state of ultrarelativistic heavy ion collisions is investigated along with transverse energy and hard process production, specifically Drell-Yan, $J/ψ$, and $Υ$ production. We choose several parton distributions and parameterizations of nuclear shadowing, as well as the spatial dependence of shadowing, to study the influence of shadowing on relevant observables. Results are presented for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and Pb+Pb collisions at $\sqrt{s_{NN}} = 5.5$ TeV.
Recent results on minijet production in nuclear collisions at the RHIC and LHC energies are reviewed. Initial conditions of the QGP at $τ=0.1$ fm$/c$, especially parton chemistry, thermalization and net baryon number-to-entropy ratio are discussed. Also, contribution of minijets from a hard BFKL-pomeron ladder will be estimated.
We show how anisotropy in momentum of the gluon distribution in ultrarelativistic heavy ion collisions gives rise to polarization of direct photons produced via gluon-quark Compton scattering, as well as by quark-antiquark annihilation into a gluon-photon pair. We estimate the polarization asymmetry from the Compton process within a toy model where the polarized photons are produced from thermal gluons scattered by heavy-quark scattering centers moving with Bjorken boost-invariant flow, and find that it could be as large as 10%. We conclude that polarization measurements of directly produced p…
Screening of initial parton production due to the presence of on-shell partons in high-energy heavy-ion collisions is discussed. It is shown that the divergent cross sections in the calculation of parton production can be regulated self-consistently without an {\it ad hoc} cut-off, and that the resultant parton production and transverse energy production rate are finite. Consequences on the energy density estimates are discussed.
Using the quasiclassical Green's function in the Coulomb field, we analyze the probabilities of single and multiple $e^+e^-$-pair production at fixed impact parameter $b$ between colliding ultrarelativistic heavy nuclei. We perform calculations in the Born approximation with respect to the parameter $Z_Bα$, and exactly in $Z_Aα$, $Z_{A}$ and $Z_{B}$ are the charge numbers of the corresponding nuclei. We also obtain the approximate formulas for the probabilities valid for $Z_Aα, Z_Bα\lesssim 1$.
One of the striking features of particle production at high beam energies is the near equal abundance of matter and antimatter in the central rapidity region. In this paper we study how this symmetry is reached as the beam energy is increased. In particular, we quantify explicitly the energy dependence of the approach to matter/antimatter symmetry in proton-proton and in heavy-ion collisions. Expectations are presented also for the production of more complex forms of antimatter like antihypernuclei.
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS energies, employing the hybrid version of the Ultrarelativistic Quantum Molecular Dynamics model, which describes the transition from a hydrodynamic stage to hadrons by the Cooper-Frye mechanism, and matches to a final hadron-resonance cascade. We fit the results both before and after the cascade stage using the Statistical Model, to assess the effect of the cascade phase. We observe a strong effect on antibaryon yields except anti-Omega, resulting in a shift in T and mu_B of the freeze-out curve. We discuss indication…
Using next-to-leading order perturbative QCD and a conjecture of saturation to suppress the production of low-energy partons, we calculate the initial energy densities and formation times for the dissipative fluid dynamical evolution of the quark-gluon plasma produced in ultrarelativistic heavy-ion collisions. We identify the framework uncertainties and demonstrate the predictive power of the approach by a good global agreement with the measured centrality dependence of charged particle multiplicities, transverse momentum spectra and elliptic flow simultaneously for the Pb+Pb collisions at the…
Coulomb corrections to perturbation theory for producing electron-positron pairs in ultrarelativistic heavy ion collisions are considered in a part-analytical, part-numerical approach. Production probabilities are reduced from perturbation theory with increasing charge of the colliding heavy ions, as has been previously argued in the literature. It is shown here that the reduction from perturbation theory comes from the appropriate physical spatial cutoff of the electromagnetic potentials arising from the colliding ultrarelativistic heavy ions.
In hydrodynamical modeling of the ultrarelativistic heavy-ion collisions the freeze-out is typically performed at a constant temperature or density. In this work we apply a dynamical freeze-out criterion, which compares the hydrodynamical expansion rate with the pion scattering rate. Recently many calculations have been done using event-by-event hydrodynamics where the initial density profile fluctuates from event to event. In these event-by-event calculations the expansion rate fluctuates strongly as well, and thus it is interesting to check how the dynamical freeze-out changes hadron distrib…
An exact solution of the two center time-dependent Dirac equation for pair production induced by ultrarelativistic heavy ion collisions is presented. Cross sections to specific final states approach those of perturbation theory. Multiplicity rates are reduced from perturbation theory.
An exact solution of the time-dependent Dirac equation for ionization and pair production induced by ultrarelativistic heavy ion collisions is presented. Exact transition probabilities, equivalent to those that would be obtained in an untruncated basis coupled channels calculation, are presented. Exact bound-electron positron pair production probabilities are calculated to be mostly smaller than those calculated with the same potential in perturbation theory at impact parameters small enough for differences to occur.
We investigate the consequences of a nonzero bulk viscosity coefficient on the transverse momentum spectra, azimuthal momentum anisotropy, and multiplicity of charged hadrons produced in heavy ion collisions at LHC energies. The agreement between a realistic 3D hybrid simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. This paves the way for an eventual quantitative determination of several QCD transport coefficients from the experimental heavy ion and hadron-nucleus collision programs.
The $γγ\toππ$ reactions are discussed. To describe those processes, we include dipion continuum, resonances, high-energy pion-pion rescatterings, $ρ$ meson exchange and pQCD Brodsky-Lepage mechanisms. The cross section for the production of pion pairs in photon-photon collisions in peripheral heavy ion collisions is calculated with the help of Equivalent Photon Approximaption (EPA) in the impact parameter space. We show predictions at $\sqrt{s_{NN}}=3.5$ TeV which could be measured e.g. by the ALICE collaboration at the LHC.
In this proceedings contribution, we will review the basics of quasiparticle anisotropic hydrodynamics. Then, we will present some recent phenomenological results of 3+1d quasiparticle anisotropic hydrodynamics and Pb-Pb $2.76$ TeV collisions from the ALICE collaboration. We show that 3+1d quasiparticle anisotropic hydrodynamics model is able to describe the experimental results for Pb-Pb collisions at $2.76$ TeV quite well for many observables such as the spectra, the elliptic flow, and HBT radii in many centrality classes.
Anisotropy in heavy-ion collisions leads to polarization of both direct and virtual photons, the latter detected via internal conversion to dileptons pairs. Thus measurement of photon polarization probes the anisotropy at all stages of collisions. In order to characterize the polarization of virtual photons, we derive here the general structure of the photon polarization operator, rho^(mu nu), in an anisotropic medium, in terms of the four spectral functions, two transverse and one longitudinal, as usual, plus a new spectral function that reflects anisotropy in asymmetric collisions; and deriv…
The space and time evolution of initial parton production in ultrarelativistic heavy ion collisions is investigated within the framework of perturbative QCD which includes both initial and final state radiations. Uncertainty principle is used to relate the life time of a radiating parton to its virtuality and momentum. The interaction time of each hard or semihard parton scattering is also taken into account. For central $Au+Au$ collisions at $\sqrt{s}=200$ GeV, most of the partons are found to be produced within 0.5 fm/c after the total overlap of the two colliding nuclei. The local momentum …
We discuss the transverse momentum distribution of thermal and prompt photons in ultrarelativistic heavy ion collisions. The prompt photons are mostly produced by fragmentation of quark jets (bremsstrahlung). If these quark jets suffer a large energy loss in heavy-ion reactions, prompt photons are significantly suppressed. Thermal electromagnetic radiation from the quark-gluon plasma and the hadron gas might then dominate the intermediate k_T-range. In central Au+Au collisions at \sqrt{s}=200A GeV, and in the range 2 GeV < k_T < 4 GeV, the inverse slope of the thermal radiation is 360-460 MeV,…
Important goals of RHIC and LHC experiments with ion beams include the creation and study of new forms of matter, such as the Quark Gluon Plasma. Heavy quark production and attenuation will provide unique tomographic probes of that matter. We predict the suppression pattern of open charm and beauty in $Au+Au$ collisions at RHIC and LHC energies based on the DGLV formalism of radiative energy loss. A cancelation between effects due to the $\sqrt{s}$ energy dependence of the high $p_T$ slope and heavy quark energy loss is predicted to lead to surprising similarity of heavy quark suppression at R…
Ratios of hadronic abundances are analyzed for pp and nucleus-nucleus collisions at sqrt(s)=20 GeV using the microscopic transport model UrQMD. Secondary interactions significantly change the primordial hadronic cocktail of the system. A comparison to data shows a strong dependence on rapidity. Without assuming thermal and chemical equilibrium, predicted hadron yields and ratios agree with many of the data, the few observed discrepancies are discussed.
The cross section for exclusive production of $π^+ π^-$ and $π^0 π^0$ meson pairs in ultrarelativistic heavy ion collisions is calculated for LHC energy $\sqrt{s_{NN}} =$ 3.5 TeV taking into account photon-photon mechanism. We concentrate on the production of large two-pion invariant masses where the mechanism of the elementary $γγ\to ππ$ process is not fully understood. In order to include a size of nuclei we perform calculation in the impact-parameter equivalent photon approximation (EPA). Realistic charge densities are used to calculate charged form factor of $^{208}$Pb nucleus and to gener…
We discuss the use of the hydrodynamic model for the description of the evolution of dense matter formed in ultrarelativistic heavy-ion collisions. The collective flow observed in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider is consistent with the assumption that a fireball of strongly interacting matter is formed. Experimental results from p-Pb and d-Au collisions show similar phenomena, which suggests that collective expansion appears in small systems as well. We review the recent application of the hydrodynamic model to small systems …
We present a realistic treatment of the hydrodynamic evolution of ultrarelativistic heavy ion collisions, based on the following features: initial conditions obtained from a flux tube approach, compatible with the string model and the color glass condensate picture; event-by-event procedure, taking into the account the highly irregular space structure of single events, being experimentally visible via so-called ridge structures in two-particle correlations; use of an efficient code for solving the hydrodynamic equations in 3+1 dimensions, including the conservation of baryon number, strangenes…
We estimate the electromagnetic effect of the spectator charge on the momentum spectra of $π^+$ and $π^-$ produced in peripheral Pb+Pb collisions at SPS energies. We find that the effect is large and results in strongly varying structures in the $x_F$ dependence of the $π^+/π^-$ ratio, especially at low transverse momenta where a deep valley in the above ratio is predicted at $x_F \sim$ 0.15 -- 0.20. It appears that the effect depends on initial conditions. Thus, it provides new information on the space and time evolution of the non-perturbative pion creation process.
The method for simulation of medium-induced rescattering and energy loss of hard partons in ultrarelativistic heavy ion collisions is developed. The model is realized as fast Monte-Carlo tool implemented to modify standard PYTHIA jet event.
We investigate the applicability of fluid dynamics in ultrarelativistic heavy ion (AA) collisions and high multiplicity proton nucleus (pA) collisions. In order for fluid dynamics to be applicable the microscopic and macroscopic distance/time scales of the system have to be sufficiently separated. The degree of separation is quantified by the ratio between these scales, usually referred to as the Knudsen number. In this work, we calculate the Knudsen numbers reached in fluid dynamical simulations of AA and pA collisions at RHIC and LHC energies. For this purpose, we consider different choices …
Global transverse-momentum conservation induces correlations between any number of particles, which contribute in particular to the two- and three-particle correlations measured in heavy-ion collisions. These correlations are examined in detail, and their importance for studies of jets and their interaction with the medium is discussed.
Combining the hydrodynamic model (Hydro code) and the transport model (PACIAE model), we present the Hydro-PACIAE hybrid model. We use the Hydro-PACIAE hybrid model to calculate Au+Au collisions at $\sqrt{s_{NN}}$=130 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The obtained pseudo-rapidity and transverse momentum distributions well reproduce the experimental data. This shows that the Hydro-PACIAE hybrid model is useful to describe the ultrarelativistic Heavy Ion Collisions at RHIC and LHC Energies. We used the hybrid model to calculate the elliptical flow for the Pb+Pb collisions at …
We manifest the origin of the wrong conclusion made by several groups of authors on the absence of Coulomb corrections to the cross section of the e^+e^- pair production in ultrarelativistic heavy-ion collisions. The source of the mistake is connected with an incorrect passage to the limit in the expression for the cross section. When this error is eliminated, the Coulomb corrections do not vanish and agree with the results obtained within the Weizsäcker-Williams approximation.
We estimate the electromagnetic effect of the spectator charge on the momentum spectra of charged pions produced in peripheral Pb+Pb collisions at SPS energies. We find a large effect which results in strongly varying structures in the $x_F$ dependence of the $π^+/π^-$ ratio, especially at low transverse momenta where a deep valley in the above ratio is predicted at $x_F \sim$ 0.15 -- 0.20. The effect depends on initial conditions. Thus, it provides new information on the space and time evolution of the non-perturbative pion creation process.
In hydrodynamical modelling of ultrarelativistic heavy-ion collisions the freeze-out is typically assumed to take place on a surface of constant temperature or energy density. In this work we apply a dynamical freeze-out criterion, which compares the hydrodynamical expansion rate with the pion scattering rate, to an event-by-event ideal hydrodynamics at the full RHIC collision energy. We present hadron spectra and elliptic flow calculated using (2+1)-dimensional ideal hydrodynamics, and show the differences between constant temperature and dynamical freeze-out criteria. We find that when the f…
We train a deep convolutional neural network to predict hydrodynamic results for flow coefficients, average transverse momenta and charged particle multiplicities in ultrarelativistic heavy-ion collisions from the initial energy density profiles. We show that the neural network can be trained accurately enough so that it can reliably predict the hydrodynamic results for the flow coefficients and, remarkably, also their correlations like normalized symmetric cumulants, mixed harmonic cumulants and flow-transverse-momentum correlations. At the same time the required computational time decreases …
Hadrons emitted by the pre-surface layer of quark-gluon plasma (QGP) before phase transition into hadronic gas are considered as possible source of direct information about QGP. It is shown that these hadrons dominate at soft p_t if QGP is created in ultrarelativistic heavy ion collisions.
We present a model for radiative energy loss of heavy quarks in quark gluon plasma which incorporates coherence effects. We then study its consequences on the radiation spectra as well as on the nuclear modification factor of open heavy mesons produced in ultrarelativistic heavy ion collisions.
It is possible that isospin violating dynamical effects are amplified due to coherence if a disoriented chiral condensate (or other source of a coherent pion state) is formed in a heavy ion collison. It is shown explicitly that altering the isospin of the coherent state by order of one unit can change the number of $π^0$'s in the condensate by some finite fraction of the total number. A possible signature of such amplified isospin violating effects is that the ratio of neutral to total low $p_T$ pions averaged over many events may differ markedly from 1/3. Such a signal would not be washed out…
The cross sections for exclusive $D^+D^-$ and $D^0 \bar {D^0}$ meson pair production in peripheral nucleus - nucleus collisions are calculated and several differential distributions are presented. The calculation of the elementary $γγ\to D \bar D$ cross section is done within the heavy-quark approximation and in the Brodsky- Lapage formalism with distribution amplitudes describing recent CLEO data on leptonic $D^+$ decay. Realistic (Fourier transform of charge density) charge form factors of nuclei are used to generate photon flux factors. Absorption effects are discussed and quantified. The c…
In this contribution, we present some predictions for the production of D and B mesons in ultrarelativistic heavy ion collisions at RHIC and LHC energies and confront them with experimental results obtained so far by the STAR, PHENIX, ALICE and CMS collaborations. We next discuss some preliminary results obtained with an improved description of the medium based on EPOS initial conditions, and its possible implications on the nuclear modification factor and on the elliptic flow of heavy quarks.
For nucleus-nucleus collisions at Relativistic-Heavy-Ion Collider (RHIC) energies we calculate observables in two conceptually transport theories, i.e. the n-body molecular dynamical model RSP and in the Parton-Hadron-String-Dynamics (PHSD), starting out from the same distribution of the initial energy density at the quark gluon plasma (QGP) formation time. The RSP is based on the Nambu Jona-Lasinio (NJL) Lagrangian whereas in PHSD the partons are described by the dynamical quasi-particle model (DQPM). Despite of the very different description of the parton properties, their interactions and o…
Basing on model concepts we research the monojet-to-dijet ratio as a function of the jet energy detection threshold in ultrarelativistic collisions of nuclei. We provide an comparative analysis of the contribution to monojet yield from gluon radiation before initial hard parton-parton scattering and from non-symmetric dijet energy losses in quark-gluon plasma, which expected to be created in ultrarelativistic heavy ion collisions.
Employing a perturbative QCD based parton cascade we calculate the elliptic flow $v_2$ and its transverse momentum dependence $v_2(p_T)$ for the gluon matter created in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. To make comparisons with the experimental data at the BNL Relativistic Heavy Ion Collider (RHIC), parton-hadron duality is assumed. We find that whereas the integrated $v_2$ matches the experimental data, the gluon (or pion) $v_2(p_T)$ is about 20-50% smaller than the experimental data. Hadronization via gluon fragmentation and quark recombination seems to be the key to explaining th…
We introduce an event-by-event perturbative-QCD + saturation + hydro ("EKRT") framework for ultrarelativistic heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading order perturbative QCD using a saturation conjecture to control soft particle production, and describe the space-time evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuth-angle asymmetries, aga…
In hydrodynamicalmodeling of heavy-ion collisions the initial state spatial anisotropies translate into momentum anisotropies of the final state particle distributions. Thus, understanding the origin of the initial anisotropies and quantifying their uncertainties is important for the extraction of specific QCD matter properties, such as viscosity, from the experimental data. In this work we study the wounded nucleon approach in the Monte Carlo Glauber model framework, focusing especially on the uncertainties which arise from the modeling of the nucleon-nucleon interactions between the collidin…
In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended collision term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab}< 100$ MeV/nucleon up to $E_{lab}> 200$ GeV/nucleon, allowing…
We discuss exclusive production of lepton-antilepton, quark-antiquark, $ππ$ and $ρ^0 ρ^0$ pairs in ultraperipheral, ultrarelativistic heavy-ion collisions. The cross sections for exclusive production of pairs of particles is calculated in Equivalent Photon Approximation (EPA). Realistic (Fourier transform of charge density) charge form factors of nuclei are used and the corresponding results are compared with the cross sections calculated with monopole form factor used in the literature. Absorption effects are discussed and quantified. The cross sections obtained with realistic form factors ar…
In ultrarelativistic heavy ion collisions, charm quark fragmentation is modified due to the melting of strings inside the high density partonic matter. D mesons produced in hadronization can further produce J/psi particles. Using a multiphase transport model, we investigate the effect on the rapidity distribution of the produced J/psi particles with two different charm quark fragmentation functions. It is shown that the J/psi rapidity distribution is sensitive to the nuclear modification of charm quark fragmentation and thus is a good indicator of the onset of string melting and the production…
We introduce a new prescription for obtaining the chemical freeze-out parameters in the heavy-ion collision experiments using the Hadron Resonance Gas model. The scheme is found to reliably estimate the freeze-out parameters and predict the hadron yield ratios, which themselves were never used in the parametrization procedure.
The method to simulate the rescattering and energy loss of hard partons in ultrarelativistic heavy ion collisions has been developed. The model is a fast Monte-Carlo tool introduced to modify a standard PYTHIA jet event. The full heavy ion event is obtained as a superposition of a soft hydro-type state and hard multi-jets. The model is applied to analysis of the jet quenching pattern at RHIC.
A significant fraction of the changes in momentum distributions induced by dissipative phenomena in the description of the fluid fireball created in ultrarelativistic heavy-ion collisions actually take place when the fluid turns into individual particles. We study these corrections in the limit of a low freeze-out temperature of the flowing medium, and we show that they mostly affect particles with a higher velocity than the fluid. For these, we derive relations between different flow harmonics, from which the functional form of the dissipative corrections could ultimately be reconstructed fro…
