A comprehensive and detailed analysis of hadronic abundances measured in Au-Au collisions at RHIC at sqrt(s)_NN = 130 and 200 GeV is presented. The rapidity densities measured in the central rapidity region have been fitted to the statistical hadronization model and the chemical freeze-out parameters determined as a function of centrality, using data from experiments BRAHMS, PHENIX and STAR. The chemical freeze-out temperature turns out to be independent of centrality to a few percent accuracy, whereas the strangeness under-saturation parameter gamma_S decreases from almost unity in central collisions to a significantly lower value in peripheral collisions. Our results are in essential agreement with previous analyses, with the exception that fit quality at sqrt(s)_NN = 200 GeV is not as good as previously found. From the comparison of the two different energies, we conclude that the difference in fit quality, as described by chi2 values, is owing to the improved resolution of measurements which has probably exceeded the intrinsic accuracy of the simplified theoretical formula used in the fits.
The single-freeze-out model with parametrized hypersurface and flow geometry is employed to analyze the transverse-momentum spectra of hadrons produced in the Pb+Pb collisions at the collision energy of {$\sqrt{s_{\rm NN}}=2.76$ TeV} at the CERN Large Hadron Collider (LHC). With the notable exception for protons and antiprotons, we find a very good agreement between the model results and the data for the measured hadron species. The additional analysis of the HBT radii of pions helps us to select, from several different types of freeze-out studied in this work, the most realistic form of the f…
I discuss the effects and quantities that influence the decoupling of particles from the fireball. The crucial role is played by the scattering rate. I show the results for the scattering rate at SPS and RHIC and discuss their implications.
I discuss the quantities and effects important for the freeze-out and outline a formalism for the description of continuous decoupling of particles from the fireball. Then I present a calculation of the scattering rates of pions at various temperatures and argue that it is important to take continuous particle decoupling into account when modelling the collision dynamics.
In hydrodynamical modeling of ultrarelativistic heavy-ion collisions, the freeze-out is typically assumed to take place at a surface of constant temperature or energy density. A more physical approach is to assume that freeze-out takes place at a surface of constant Knudsen number. We evaluate the Knudsen number as a ratio of the expansion rate of the system to the pion scattering rate, and apply the constant Knudsen number freeze-out criterion to ideal hydrodynamical description of heavy-ion collisions at RHIC ($\sqrt{s_\mathrm{NN}}=200$ GeV) and the LHC ($\sqrt{s_\mathrm{NN}}=2760$ GeV) ener…
We explore the consequences of a freeze-out criterion for heavy-ion collisions, based on pion escape probabilities from the hot and dense but rapidly expanding collision region. The influence of the expansion and the scattering rate on the escape probability is studied. The temperature dependence of this scattering rate favors a low freeze-out temperature of ~100 MeV. In general, our results support freeze-out along finite four-volumes rather than sharp three-dimensional hypersurfaces, with high-pt particles decoupling earlier from smaller volumes. We compare our approach to the proposed unive…
An alternative, to the commonly used blast-wave, model describing the freeze-out hypersurface is applied to fit the $p_{T}$-spectra of identified hadrons measured at relativistic heavy-ion collisions at $\sqrt{s_{NN}}=62.4, 130$ and 200 GeV. Decays of resonances are taken into account completely. It has turned out that the fitted freeze-out temperature and baryon number chemical potential depend weakly on the centrality of the collision and their values are close to the chemical freeze-out values determined from fits to particle yield ratios.
We present an analysis of hadronic multiplicities measured in Pb-Pb collisions at \sqrt s_{NN} = 2.76 TeV as a function of the collision centrality within the statistical hadronization model. Evidence is found of a dependence of the chemical freeze-out temperature as a function of centrality, with a slow rise from central to peripheral collisions, which we interpret as an effect of post-hadronization inelastic scatterings. Using correction factors calculated by means of a simulation based on the UrQMD model, we are able to obtain a significant improvement in the statitical model fit quality an…
In this article, we will present a systematic analysis of transverse momentum spectra of the strange hadron in different multiplicity events produced in pp collision at $\sqrt{s}$ = 7 TeV, pPb collision at $\sqrt{s_{NN}}$ = 5.02 TeV and PbPb collision at $\sqrt{s_{NN}}$ = 2.76 TeV. The differential freeze out scenario of strange hadron $K^{0}_{s}$ assumed while analyzing the data using a Tsallis distribution which is modified to include transverse flow. The $p_{T}$ distributions of strange hadron in different systems are characterized in terms of the parameters namely, Tsallis temperature ($T$…
We estimate chemical freeze-out parameters in HRG and EVHRG model by fitting the experimental information of net-proton and net-charge fluctuations measured in Au + Au collisions by the STAR collaboration at RHIC. We observe that chemical freeze-out parameters obtained from lower and higher order fluctuations are though almost same for $\sqrt{s_{NN}} > 27$ GeV, tend to deviate from each other at lower $\sqrt{s_{NN}}$. Moreover, these separations increase with decrease of $\sqrt{s_{NN}}$ and for a fixed $\sqrt{s_{NN}}$ increase towards central collisions. Furthermore, we observe an approximate …
In this paper we use methods developed in Part 1 of The Dipion Cocktail, to fit the $p_t$ dependence of dipions for mid-central Au-Au collisions at $\sqrt{s_{NN}}$=200 GeV. For the minijet fragmentation part we use PYTHIA fragmentation as described in Part 1. For the thermal resonance production we use an exponential growth behavior. The interference between the direct production of dipion pairs from non-resonance minijet fragmentation and re-scattering through resonance states gives a measure of the size of the re-scattering region. This size is contain in the $α$ parameter of Part1. We assum…
We will report centrality dependence of chemical freeze-out temperature ($T_{ch}$), light quark chemical potential ($μ_{q}$), strange quark chemical potential ($μ_{s}$), and strangeness saturation factor ($γ_{s}$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 and 200 GeV. A systematic study for combination of ratios for chemical freeze-out fit is studied and we have found small ombination dependences. The results show $γ_{s}$ increasing with centrality but the other parameters have less sensitivity to the centralities.
We perform a systematic analysis of several HBT parameters in heavy ion collisions from $E_{\rm beam}=2$ AGeV to $\sqrt {s_{\rm NN}}=200$ GeV within the UrQMD transport approach and compare the results to experimental data where available. We find that the 'lifetime' of the emission source as calculated from $τ\sim \sqrt{R_O^{2}-R_S^{2}}$, is larger than the experimentally observed values at all investigated energies. The calculated volume of the pion source ($V_f$) is found to increase monotonously with increasing beam energy and the experimentally observed decrease of the measured $V_f$ at A…
We confront the hypothesis of chemical freeze-out in ultra-relativistic heavy-ion collisions with the hypothesis of large modifications of hadron masses in nuclear medium. We find that the thermal-model predictions for the ratios of particle multiplicities are sensitive to the values of in-medium hadronic masses. In particular, the $π^+/p$ ratio decreases by 35% when the masses of all hadrons (except for pseudo-Goldstone bosons) are scaled down by 30%.
We study the effect of separate chemical and kinetic freeze-outs to the ideal hydrodynamical flow in Au+Au collisions at RHIC (sqrt(s_NN) = 200 GeV energy). Unlike in earlier studies we explore how these effects can be counteracted by changes in the initial state of the hydrodynamical evolution. We conclude that the reproduction of pion, proton and antiproton yields necessitates a chemical freeze-out temperature of T = 150 MeV instead of T = 160 - 170 MeV motivated by thermal models. Unlike previously reported, this lower temperature makes it possible to reproduce the p_T-spectra of hadrons if…
We argue that known systematics of hadron cross sections may cause different particles to freeze out of the fireball produced in heavy-ion collisions at different times. We find that a simple model with two freezeout points is a better description of data than that with a single freezeout, while still remaining predictive. The resulting fits seem to present constraints on the late stage evolution of the fireball, including the tantalizing possibility that the QCD chiral transition influences the yields at sqrt(S)=2700 GeV and the QCD critical point those at sqrt(S)=17.3 GeV.
We discuss the production of light nuclei in heavy ion collisions within a multiple freezeout scenario. Thermal parameters extracted from the fits to the observed hadron yields are used to predict the multiplicities of light nuclei. Ratios of strange to non strange nuclei are found to be most sensitive to the details of the chemical freezeout. The well known disagreement between data of $^3_Λ\text{H/}^3\text{He}$ and $\overline{^3_Λ\text{H/}^3\text{He}}$ at $\sqrt{s_{NN}}=200$ GeV and models based on thermal as well as simple coalescence using a single chemical freezeout surface goes away when…
Measurements of three-dimensional correlation functions of like-sign low transverse momentum kaon pairs from Au+Au collisions at top RHIC energy $\sqrt s_{NN}$=200 GeV are presented. The extracted kaon source function is narrower than the pion one and does not have the long tail along the pair transverse momentum direction. This indicates a much smaller role of long-lived resonance decays and/or of the emission duration on kaon emission. Three-dimensional Gaussian shape of the kaon source function can be adequately reproduced by Therminator simulations with resonance contributions taken into a…
The particle production and their ratios for $π$, $K$, $p$, and $Λ$ are studied in Pb + Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV based on a blast-wave model with thermal equilibrium mechanism. The transverse momentum spectra of the above mentioned particles at the kinetic freeze-out stage are discussed. The modification of the inverse slope of pion transverse momentum spectrum due to resonance decay has also been investigated. In addition, we found that the anti-particles to particles ratio as well as kaons to pions ratio agree with the data by the LHC-ALICE Collaboration reasonably well, w…
Many data in the high energy physics are, in fact, sample means. It is shown that when this exact meaning of the data is taken into account and the most weakly bound states are removed from the hadron resonance gas, the acceptable fit to the whole spectra of pions, kaons and protons measured at midrapidity in central Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV [Phys.Rev.Lett.109,252301(2012)] is obtained. The invariant distributions are predicted with the help of the single-freeze-out model in the chemical equilibrium framework. Low $p_{T}$ pions and protons are reproduced simultaneously as…
Using a covariant quark coalescence model combined with a blast-wave-like analytical parametrization for (anti-)strange quark phase-space freeze-out configuration, we extract information on strange quark freeze-out dynamics in Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV by fitting the measured transverse momentum spectra and elliptic flows ($v_2$) of $ϕ$ mesons and $Ω$ baryons. We find that although both the measured and calculated $v_2$ of $ϕ$ and $Ω$ satisfy the number-of-constituent-quark (NCQ) scaling, the NCQ-scaled $v_2$ is significantly smaller than the $v_2$ of strange quarks, implyin…
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…
The collision system and multiplicity dependence of chemical freeze-out temperature ($T_{\rm ch}$) and strangeness saturation factor ($γ_{s}$) are obtained by studying the particle ratios at the Large Hadron Collider (LHC) energies. Here, we consider the new results in pp at 13 TeV, p+Pb at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, Xe+Xe at $\sqrt{s_{\rm NN}}$ = 5.44 TeV and Pb+Pb at $\sqrt{s_{\rm NN}}$ = 5.02 TeV along with the earlier results in pp at $\sqrt{s}$ = 7 TeV and Pb+Pb at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. A statistical thermal model is used to extract the chemical freeze-out parameters in dif…
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.
Collective Flow, Kinetic Freeze-Out, and a Data-Driven Baryon Chemical Potential in Au+Au Collisions at $\sqrt{s_{NN}} = 7.7$--$39$ GeV
Department of Physics, Aligarh Muslim University（阿利加尔穆斯林大学物理系）；School of Physical Sciences, National Institute of Science Education and Research（国家科学教育与研究学院物理科学学院）；Homi Bhabha National Institute（霍米·巴巴国立研究所）
Comment on "Evaluation of kinetic freeze-out properties in different relativistic heavy-ion collision systems at \sqrtsNN = 200 GeV'' (Eur. Phys. J. Plus (2025) 140:179) https://doi.org/10.1140/epjp/s13360-025-06119-0
We present a summary of the recent results obtained with the novel hadron resonance gas model with the multicomponent hard-core repulsion which is extended to describe the mixtures of hadrons and light (anti-, hyper-)nuclei. A very accurate description is obtained for the hadronic and the light nuclei data measured by STAR at the collision energy $\sqrt{s_{NN}} =200$ GeV and by ALICE at $\sqrt{s_{NN}} =2.76$ TeV. The most striking result discussed here is that for the most probable chemical freeze-out scenario for the STAR energy the found parameters allow us to reproduce the values of the exp…
The event-shape and multiplicity dependence of the chemical freeze-out temperature ($T_{\text{ch}}$), freeze-out radius ($R$), and strangeness saturation factor ($γ_{s}$) are obtained by studying the particle yields from the PYTHIA8 Monte Carlo event generator in proton-proton (pp) collisions at the centre-of-mass $\sqrt{s}$ = 13 TeV. Spherocity is one of the transverse event-shape techniques to distinguish jetty and isotropic events in high-energy collisions and helps in looking into various observables in a more differential manner. In this study, spherocity~classes are divided into three ca…
We formulate a freeze-out criterion for ultra-relativistic heavy ion collisions in terms of the pion escape probability from the collision region. We find that the increase in pion phase-space density from SPS to RHIC reported at this conference has a small influence on particle freeze-out because of the small pi-pi cross-section. Our treatment takes into account dynamical expansion, chemical composition and momentum of the escaping particle for particle freeze-out. It supports a freeze-out at rather low temperature - below 100 MeV - and earlier decoupling of high p_t particles.
Global evolution of the matter in relativistic collisions of heavy nuclei and the resulting global freeze-out parameters are analyzed in a wide range of incident energies 2.7 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The analysis is performed within the three-fluid model employing three different equations of state (EoS): a purely hadronic EoS, an EoS with the first-order phase transition and that with a smooth crossover transition. Global freeze-out parameters deduced from experimental data within the statistical model are well reproduced within the crossover scenario. The 1st-order-transition scena…
We study the rapidity spectra in ultra-relativistic heavy ion collisions in the framework of the Landau hydrodynamical model. We find that thermal smearing effects improve the agreement with experimental results on pion rapidity spectra. We describe a simple model of the hadronization and discuss its consequences regarding the pion multiplicity and the increasing entropy condition.
The thermodynamic parameters like energy density, pressure, entropy density, temperature and particle density are determined from the transverse momentum distributions of charged particles in Pb-Pb collisions at the LHC. The results show a clear increase with the centrality and the beam energy in all parameters. It is determined that in the final freeze-out stage the energy density reaches a value of about 0.039 GeV/fm$^3$ for the most central collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. This is less than that at chemical freeze-out where the energy density is about 0.36 GeV/fm$^3$. This decrease…
We discuss the $\sqrt{s}$-dependence of the $K^+/π^+$ ratio in heavy-ion collisions (the "horn" effect) within a Mott-Anderson localization model for chemical freeze-out. The different response of pion and kaon radii to the hot and dense hadronic medium results in different freeze-out conditions. We demonstrate within a simple model that this circumstance enhances the "horn" effect relative to statistical models with universal chemical freeze-out.
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 dec…
The freezeout conditions in proton-proton collisions at $\sqrt{s_{\textrm{NN}}}= 200$, $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields at mid-rapidity within the framework of the statistical model of an ideal gas of hadrons and resonances in the grand canonical ensemble. The variation of the extracted freezeout thermal parameters and the goodness of the fits with $\sqrt{s_{\textrm{NN}}}$ are discussed. We find the extracted temperature and baryon chemical potential of the freezeout surface to be similar in p+p and heavy ion collisions. On the other hand, the thermal …
We investigate the rapidity dependence of the elliptical flow in heavy ion collisions at 200 GeV (cms), by employing a three-dimensional hydrodynamic evolution, based on different initial conditions, and different freeze-out scenarios. It will be shown that the form of pseudo-rapidity ($η$) dependence of the elliptical flow is almost identical to space-time-rapidity ($η_{s}$) dependence of the initial energy distribution, independent of the freeze-out prescriptions.
The particle production of Kaon and $Λ$ are studied in nucleus-nucleus collisions at relativistic energy based on a chemical equilibrium blast-wave model. The transverse momentum spectra of Kaon and $Λ$ at the kinetic freeze-out stage from our model are in good agreement with the experimental results. The kinetic freeze-out parameters of temperature ($T_{kin}$) and radial flow parameter $ρ_{0}$ are presented for the FOPI, RHIC and LHC energies. And the resonance decay effect is also discussed. The systematic study for beam energy dependence of the strangeness particle production will help us t…
We consider hadron production in high energy collisions as an Unruh radiation phenomenon. This mechanism describes the production pattern of newly formed hadrons and is directly applicable at vanishing baryochemical potential, mu = 0. It had already been found to correctly yield the hadronisation temperature, T_h = sqrt(sigma / 2 pi) = 165 MeV in terms of the string tension sigma. Here we show that the Unruh mechanism also predicts hadronic freeze-out conditions, giving s/T_h^3 = 3 pi^2 / 4 = 7.4 in terms of the entropy density s and E/N = \sqrt(2 pi sigma) = 1.09 for the average energy per ha…
Ratio of the yield of strange hadrons to pions is considered as an important observable in studying the properties of the system produced in relativistic heavy ion collisions. Production of strange hadrons $K, \bar{K}, Λ, Σ, Ξ$ and $Ω$ have been evaluated microscopically using rate equations by considering their hadronic interaction cross sections in an expanding medium. The yields obtained from rate equations are normalized with thermal pions and compared with the measurements from Pb-Pb collisions at various multiplicities at LHC energy. The calculation has been done for various initial and …
We analyse the transverse momentum ($p_{\rm T}$)-spectra as a function of charged-particle multiplicity at midrapidity ($|y| < 0.5$) for various identified particles such as $π^{\pm}$, $K^{\pm}$, $K_S^0$, $p+\overline{p}$, $ϕ$, $K^{*0} + \overline {K^{*0}}$, and $Λ$ + $\barΛ$ in proton-proton collisions at $\sqrt{s}$ = 7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity dependent kinetic freeze-out temperature ($T_{\rm kin}$) and radial flow ($β$) of various particles after fitting the $p_{\rm T}$-distri…
The modified model emission function S(x,p), with a uniform radial expansion mode and mass reduction, is used to study the single particle spectra and two particle correlation of pions. The calculated HBT radii and one particle spectra are compared with the data from $\sqrt(S_NN)$=130 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). We see the main features of the data are reproduced, Ro/Rs decreases with increasing Kt and we have a kinetic freeze out temperature T=150 MeV.
The recently developed hadron resonance gas model with multicomponent hard-core repulsion is used to address and resolve the long standing problem to describe the light nuclear cluster multiplicities including the hyper-triton measured by the STAR Collaboration, known as the hyper-triton chemical freeze-out puzzle. An unprecedentedly accurate description is obtained for the hadronic and other light nuclear cluster data measured by STAR at the collision energy $\sqrt{s_{NN}} =200$ GeV and by ALICE at $\sqrt{s_{NN}} =2.76$ TeV. This success is achieved by applying the new strategy of analyzing t…
The recently discovered sharp peak in the excitation function of the K+/pi+ ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model, the freeze-out of an ideal hadron gas changes from a situation where baryons dominate to one with mainly mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The calculated maximum in the K+/pi+ ratio is, however, much less pronounced than the one observed by the NA49 Collaboration. The smoo…
In this paper, we investigate the kinetic freeze-out properties in relativistic heavy ion collisions at different collision energies. We present a study of standard Boltzmann-Gibbs Blast-Wave (BGBW) fits and Tsallis Blast-Wave (TBW) fits performed on the transverse momentum spectra of identified hadrons produced in Au + Au collisions at collision energies of $\sqrt{s_{\rm{NN}}}=$ 7.7 - 200 GeV at the Relativistic Heavy Ion Collider (RHIC), and in Pb + Pb collisions at collision energies of $\sqrt{s_{\rm{NN}}}=$ 2.76 and 5.02 TeV at the Large Hadron Collider (LHC). The behavior of strange and m…
Centrality-dependent double-differential transverse momentum spectra of charged pions, kaons, and (anti)protons produced in mid-pseudorapidity interval in $\sqrt{s_{NN}}=200$ GeV gold-gold and deuteron-gold collisions with different centralities are analyzed by the blast-wave model with Boltzmann-Gibbs statistics. Meanwhile, the mentioned spectra in mid-rapidity interval in $\sqrt{s_{NN}}=2.76$ TeV lead-lead and $\sqrt{s_{NN}}=5.02$ TeV proton-lead collisions with different centralities are analyzed by the same model. The model results are approximately in agreement with the experimental data …
The status of thermal model descriptions of particle production in heavy ion collisions is presented. We discuss the formulation of statistical models with different implementation of the conservation laws and indicate their applicability in heavy ion and elementary particle collisions. We analyze experimental data on hadronic abundances obtained in ultrarelativistic heavy ion collisions, in a very broad energy range starting from RHIC/BNL ($\sqrt s=200$ A GeV), SPS/CERN ($\sqrt s\simeq 20$ A GeV) up to AGS/BNL ($\sqrt s\simeq 5$ A GeV) and SIS/GSI ($\sqrt s\simeq 2$ A GeV) to test equilibrati…
The transverse momentum ($p_{\rm T}$) spectra in proton-proton collisions at $\sqrt{s}$ = 7 TeV, measured by the ALICE experiment at the LHC are analyzed with a thermodynamically consistent Tsallis distribution. The information about the freeze-out surface in terms of freeze-out volume, temperature and the non-extenisivity parameter, $q$, for $K^{0}_{S}$, $Λ+\barΛ$, $Ξ^{-}+\barΞ^{+}$ and $Ω^{-}+\barΩ^{+}$ are extracted by fitting the $p_{\rm T}$ spectra with Tsallis distribution function. The freeze-out parameters of these particles are studied as a function of charged particle multiplicity de…
We fit the single-particle $p_t$ spectra of identified pions, kaons, and (anti)protons from central collisions of gold or lead nuclei at energies between 7.7 and 2760~GeV per nucleon pair. Blast wave model with included resonance production and with an assumption of partial chemical equilibrium is used and the fits are performed with the help of a Gaussian emulator process. A kinetic freeze-out temperature is found about 100~MeV for the lowest collision energies and 80~MeV at the LHC. The average transverse expansion velocity grows with increasing $\sqrt{s_{NN}}$ from 0.45 to 0.65. Due to part…
We show that the measured yield ratio $^3_Λ$H/$^3$He ($^3_{\overlineΛ}\overline{\text{H}}$/$^3\overline{\text{He}}$) in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV can be understood within a covariant coalescence model if (anti-)$Λ$ particles freeze out earlier than (anti-)nucleons but their relative freezeout time is closer at $\sqrt{s_{NN}}=2.76$ TeV than at $\sqrt{s_{NN}}=200$ GeV. The earlier (anti-)$Λ$ freezeout can significantly enhance the yield of (anti)hypernucleus $^4_Λ$H ($^4_{\overlineΛ}\overline{\text{H}}$), leading to that $^4_{…
Here we develop the hadron resonance gas model with the Gaussian width of hadron resonances. This model allows us to treat the usual hadrons and the quark gluon bags on the same footing and to study the stability of the results obtained within different formulations of the hadron resonance gas model. In this work we perform a successful fit of 111 independent hadronic multiplicity ratios measured for $\sqrt{s_{NN}} $= 2.7- 200 GeV. We demonstrate that in a narrow range of collision energy $\sqrt{s_{NN}} =$ 4.3-4.9 GeV there exist peculiar irregularities in various thermodynamic quantities foun…
Using the UrQMD/coarse graining approach we explore the kinetic freeze-out stage in central Au + Au collisions at various energies. These studies allow us to obtain detailed information on the thermodynamic properties (e.g. temperature and chemical potential) of the system during the kinetic decoupling stage. We explore five relevant collision energies in detail, ranging from $\sqrt{s_{NN}}=2.4\,\mathrm{GeV}$ (GSI-SIS) to $\sqrt{s_{NN}}=200\,\mathrm{GeV}$ (RHIC). By adopting a standard Hadron Resonance Gas equation of state, we determine the average temperature $\langle T \rangle$ and the aver…
Three possible scenarios of the statistical hadronization model are reexamined with the use of the $p_{T}$ spectra of the PHENIX and very low $p_{T}$ PHOBOS measurements at $\sqrt{s_{NN}}=200$ GeV. These scenarios are: (\textit{a}) full chemical non-equilibrium, (\textit{b}) strangeness chemical non-equilibrium and (\textit{c}) chemical equilibrium. Fits to the spectra are done within the Cracow single-freeze-out model, which takes into account both the expansion and resonance decays. Predictions for spectra of $ϕ$, $K(892)^{\ast 0}$ and $π^{0}$ are also given. The global variables like the tr…
Using the moments of the net-kaon distribution calculated within a state of-the-art hadron resonance gas model compared to experimental data from STAR's Beam Energy Scan, we find that the extracted strange freeze-out temperature is incompatible with the light one extracted from net-proton and net-charge fluctuations. Additionally predictions for net-$Lambda$ fluctuations are made that also appear to be consistent with a higher freeze-out temperature for strange particles. This strangeness freeze-out temperature is roughly $10-15$ MeV higher than the corresponding light freeze-out temperature. …
Driven by the Beam Energy Scan (BES) program at the RHIC, researches and discussions on the QCD phase diagram have flourished recently. In order to provide a reference from microscopic transport models, we performed a systematic analysis, using a multiphase transport (AMPT) model for the particle yields and a statistical model (THERMUS) for the thermal fit, for Au+Au collisions at $\sqrt{s_{\text{NN}}}$=7.7-200 GeV. It is found that at a fixed collision centrality the chemical freeze-out parameter, temperature $T_{\text{ch}}$, increases with collision energy and somehow saturates at certain va…
We fit the single-hadron transverse-momentum spectra measured in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV with the blast-wave model that includes production via resonance decays. Common fit to pions, kaons, (anti)protons, and lambdas yields centrality dependence of the freeze-out temperature and transverse expansion velocity. In the most central collisions we see $T=98$ MeV and $\langle v_t \rangle = 0.654$. The $K^*$ resonance fits into this picture but the $ϕ$ meson might freeze-out a little earlier. Multistrange baryons seem to decouple at higher temperature and weaker transverse flow…
We explain how event-by-event fluctuations of particle ratios can constrain and falsify the statistical model of particle production in heavy ion collisions, using $K/π$ fluctuations as an example. We define an observable capable of determining which statistical model, if any, governs freeze-out in ultrarelativistic heavy ion collisions. We calculate this observable for $K/π$ fluctuations, and show that it should be the same for RHIC and LHC energies, as well as independent of centrality, if the Grand-Canonical statistical model is an appropriate description and chemical equilibrium applies. W…
We present lattice QCD results along the freezeout curve of heavy-ion collisions for the ongoing RHIC energy scan as well as the LHC heavy-ion runs planned for this year. The skew and kurtosis of the event distribution of baryon number are positive at all energies studied, We predict three ratios of non-linear susceptibilities along the freezeout curve as functions of the colliding energy, Sqrt[S_{NN}]. They have smooth behaviour except in the vicinity of a critical point; this can have multiple benefits.
