System size dependence of freeze-out properties at RHIC
A. Iordanova, O. Barannikova, R. S. Hollis
备注：
6 pages, 6 figures, poster proceedings for the Quark Matter 2006 Conference, Shanghai, China, 14th-20th Novermber 2006, submitted to the International Journal of Modern Physics E
The STAR experiment at RHIC has measured identified pi(+/-), K(+/-) and p(pbar) spectra and ratios from sqrt(s_NN) = 62.4 and 200 GeV Cu+Cu collisions. The new Cu+Cu results are studied with hydro-motivated blast-wave and statistical model frameworks in order to characterize the freeze-out properties of this system. Along with measurements from Au+Au and p+p collisions, the obtained freeze-out parameters are discussed as a function of collision energy, system size, centrality and inferred energy density. This multi-dimensional systematic study reveals the importance of the collision geometry and furthers our understanding of the QCD phases.
Investigation of the final hadronic state properties of ultra-relativistics pp and Au+Au collisions supplies information on freeze-out conditions at RHIC and possible insights into early stages of these collisions. A variety of particle spectra measured by STAR are studied within the framework of chemical and local kinetic equlibrium models. Here we present the extracted chemical and final kinetic freeze-out temperatures, strangeness saturation factor, final collective flow velocity, and the inferred flow velocity at chemical freeze-out. In light of those measurements we disscuss dynamical evo…
The intermediate $p_T$ region (2 - 5 GeV/$c$) in central Au+Au collisions at RHIC has a rich physics content. The (anti)proton to pion ratio at the intermediate $p_T$ gives us a powerful tool to investigate the bulk properties of the hot and dense matter created at RHIC and their hadronization processes. We present the preliminary results of identified charged hadron spectra at the lower beam energies at RHIC. The excitation function of (anti)proton to pion ratios from SPS to RHIC are shown. We also discuss the onset of the baryon enhancement at the high energy heavy ion collisions.
We present the results of a systematic test applying statistical thermal model fits in a consistent way for different particle ratios, and different system sizes using the various particle yields measured in the STAR experiment. Comparison between central and peripheral Au+Au and Cu+Cu collisions with data from p+p collisions provides an interesting tool to verify the dependence with the system size. We also present a study of the rapidity dependence of the thermal fit parameters using available data from RHIC in the forward rapidity regions and also using different parameterization for the ra…
The STAR Collaboration has measured two-pion correlation functions versus emission angle with respect to the event plane in non-central Au+Au collisions at \sqrt{s_{NN}}=130, 200 GeV. In the context of a parameterized freezeout scenario, the data suggest an out-of-plane freezeout geometry, and a rapid system evolution to freezeout.
Identified charged kaon, pion, and proton spectra and ratios from sqrt(s_NN) = 200 and 62.4 GeV Cu+Cu collisions are studied with a hydro-motivated blast-wave and a statistical model framework in order to explore the strangeness production at RHIC and characterize the bulk freeze-out properties of the created system. The spectra are measured at mid-rapidity |y|<0.1 over the transverse momentum range of 0.25 < p_T < 1.2 GeV/c with particle identification derived from the ionization energy loss in the STAR Time Projection Chamber. The multi-dimensional systematic study of pi(+/-), K(+/-), p and …
Measurements of a variety of hadron species in pp and Au+Au collisions at 200 GeV are presented and studied within the framework of chemical and local kinetic equilibrium models. The extracted chemical and final kinetic freeze-out temperatures and collective flow velocities are discussed as function of centrality. The results suggest that Au+Au collisions of various centralities at RHIC always evolve toward the same temperature at chemical freeze-out, followed by cooling and expansion toward kinetic freeze-out.
We discuss details of our thermal model applied to extract chemical freeze-out conditions from fluctuations in the net-electric charge and net-proton number measured at RHIC. A parametrization for these conditions as a function of the beam energy is given.
Resonance yields and spectra from elementary p+p and Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 200 GeV from the STAR experiment at RHIC are presented and discussed in terms of chemical and thermal freeze-out conditions. Thermal models do not adequately describe the yields of the resonance production in central Au+Au collisions. The approach to include elastic hadronic interactions between chemical freeze-out and thermal freeze-out suggests a time of $Δτ>$5 fm/c.
We report the measurements of the transverse momentum spectra and invariant mass distributions of $Δ$(1232)$\to πp$, $K^*$(892)$^{0,\pm} \to πK$ and $ρ$(770)$^{0} \to π^{+} π^{-}$ in Au+Au and p+p collisions at $\sqrt{s_{NN}}$=200 GeV using the STAR TPC at RHIC. These resonances provide sensitive probes to examine the evolution dynamics in the hadronic medium through their decay and regeneration processes. The particle ratios of $K^*/K$, $K^*/ϕ$, $Δ$/p and $ρ/π$, the $K^*$, $ρ$ and $Δ$ apparent masses and the dependence of these quantities on centrality provide evidence of dynamical interactio…
Strange particle ratios and pT-spectra are calculated in a thermal model with single freeze-out, previously used successfully to describe non-strange particle production at RHIC. The model and the recently released data for phi, Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing that the thermal approach can be used to describe the strangeness production at RHIC.
We extract chemical freeze-out conditions via a thermal model approach from fluctuation observables measured at RHIC and compare with results from lattice QCD and statistical hadronization model fits. The possible influence of additional critical and non-critical fluctuation sources not accounted for in our analysis is discussed.
Light antinuclei may be formed in relativistic heavy ion collisions via final state coalescence of antinucleons. The yields of antinuclei are sensitive to primordial antinucleon production, the volume of the system at kinetic freeze-out, and space-momentum correlations among antinucleons at freeze-out. We report here preliminary STAR results on antideuteron and antihelion production in 130A GeV Au+Au collisions. These results are examined in a coalescence framework to elucidate the space-time structure of the antinucleon source.
The production and freeze-out conditions of strange particles, produced in Au+Au collisions at RHIC energies, are studied within microscopic transport model. The system of final particles can be represented as a core, containing the particles which are still interacting with each other, and a halo, in which the particles have already decoupled from the system. In microscopic calculations hadrons are continuously emitted from the whole reaction volume. At RHIC, however, significant fractions of both mesons and baryons are emitted from the surface region within the first two fm/c. Different spec…
(Abstract is abridged for arXiv.) Identified mid-rapidity particle spectra and freeze-out properties are presented for 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions, measured in the STAR-TPC. Evolution of the identified particle spectra ($π^{\pm}$, $K^{\pm}$, p and $\overline{p}$) with charged particle multiplicity and event centrality is investigated in detail. Thermal model fits to the measured particle ratios yield a chemical freeze-out temperature $\sim$ 155 MeV in 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions. The extracted chemical freeze-out temperature is close to the c…
Recent results of $Λ$(1520) resonance production in d+Au collisions at $\sqrt{s_{\rm NN}} = $ 200 GeV are presented and discussed in terms of the evolution and freeze-out conditions of a hot and dense fireball medium. Yields and spectra are compared to results from p+p and Au+Au collisions. The $Λ$(1520)/$Λ$ ratio in d+Au collisions ratio is consistent with the ratio in p+p collisions. This suggests a short time for elastic interactions between chemical and thermal freeze-out. One can conclude that the interaction volume in d+Au collisions is small.
The single-freeze-out model of hadron production is used to describe the particle ratios and the transverse-momentum spectra from RHIC. The emphasis is put on the new measurements done at the highest beam energy of 200 GeV. An overall very good agreement is found between the data and the model predictions. The data for different centrality windows are analyzed separately. A simple scaling of the two expansion parameters of the model with the centrality is found. Interestingly, this scaling turns out to be equivalent to the scaling of hadron production with the number of wounded nucleons.
The transverse momentum spectra at RHIC and LHC for A+A and p+p collisions are studied with Tsallis distributions in different approaches i.e. with and without radial flow. The information on the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocities for different particle species are obtained. These parameters are found to show a systematic behavior with mass dependence. It is observed that the heavier particles freeze-out early as compared to lighter particles and freeze-out surfaces are different for different particles, which is a direc…
Systematic trend of the hadron freeze-out conditions from AGS/SPS to RHIC is discussed. The most interesting results from collisions at RHIC are that the system is indeed approaching net-baryon free and the transverse expansion is much stronger than that from collisions at AGS/SPS energies. In order to understand the trend of the collective velocity, an energy scan between $\sqrt{s_{NN}} = 20 - 200 GeV, is important. In addition, systematic studies on the anisotropy parameter $v_2$ and the transverse momentum distributions of $ϕ, Ω,$ and $J / ψ$ are necessary as they will help in determining w…
The STAR detector at RHIC, due to its large uniform acceptance and excellent particle identification capabilities, has measured a variety of hadron species ($π^{\pm}$, $K^{\pm}$, $p$, $\bar{p}$, $K^{0}_{S}$, $Λ$, $\barΛ$, $Ξ^{-}$, $\barΞ^{+}$) produced in Au+Au collisions at $\sqrt {s_{NN}}= 7.7$, 11.5, 27 and 39 GeV. These data are part of the Beam Energy Scan (BES) program at RHIC and provide an opportunity to measure the yields and transverse momentum spectra ($p_{T}$) of the particles produced in the collisions. The corresponding measurements allow to study the freeze-out properties and dy…
We investigate the form of the viscous correction to the equilibrium distribution function in the context of a Cooper-Frye freeze out prescription for viscous hydrodynamic simulations of relativistic heavy ion collisions. The standard quadratic ansatz used by all groups for the case of shear viscosity is found to be disfavored by experimental data for v4/(v2)^2 at the Relativistic Heavy Ion Collider, and is unlikely to be correct for the hadron resonance gas present at freeze out. Instead, data for v2(pt) along with v4/(v2)^2 favor a momentum dependence between linear and quadratic.
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 …
The experimental data from the RHIC and LHC experiments of invariant pT spectra in A+A and p + p collisions are analysed with Tsallis distributions in different approaches. The information about the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocity for different particle species are obtained. Further, these parameters are studied as a function of the mass of the secondary particles. A mass-dependent differential freeze-out is observed which does not seem to distinguish between particles and their antiparticles. Further a mass-hierarchy i…
The STAR experiment at RHIC has completed its first phase of the Beam Energy Scan (BES-I) program to understand the phase structure of the quantum chromodynamics (QCD). The bulk properties of the system formed in Au+Au collisions at different center of mass energy $\sqrt{s_{NN}} = $ 7.7, 11.5, 19.6, 27, and 39 GeV have been studied from the data collected in the year 2010 and 2011. The centrality and energy dependence of mid-rapidity ($|y|$ < 0.1) particle yields, and ratios are presented here. The chemical freeze-out parameters are extracted using measured particle ratios within the framework…
The relaxation of hot nuclear matter to an equilibrated state in the central zone of heavy-ion collisions at energies from AGS to RHIC is studied within the microscopic UrQMD model. It is found that the system reaches the (quasi)equilibrium stage for the period of 10-15 fm/$c$. Within this time the matter in the cell expands nearly isentropically with the entropy to baryon ratio $S/A = 150 - 170$. Thermodynamic characteristics of the system at AGS and at SPS energies at the endpoints of this stage are very close to the parameters of chemical and thermal freeze-out extracted from the thermal fi…
We present calculations of the chemical freeze-out temperature (T_ch) based on particle yields from STAR and ALICE measured at collision energies ranging from sqrt{s_{NN}} = 11.5 GeV to 5.02 TeV. Employing the Grand Canonical Ensemble approach using the Thermal-FIST Hadron Resonance Gas model package, we show evidence for a flavour-dependent chemical freeze-out in the crossover region of the QCD phase diagram. At a vanishing baryochemical potential, we calculate light and strange flavour freeze-out temperatures T_L = 150.2 +- 2.6 MeV and T_S = 165.1 +- 2.7 MeV, respectively.
The first phase of Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) was started in the year 2010 with the aim to study the several aspects of the quantum chromodynamics (QCD) phase diagram. The Solenoidal Tracker At RHIC (STAR) detector has taken data at $\sqrt{s_{NN}} = $ 7.7, 11.5, 19.6, 27, and 39 GeV in Au+Au collisions in the years 2010 and 2011 as part of the BES programme. For these beam energies, we present the results on the particle yields, average transverse mass and particle ratios for identified particles in mid-rapidity ($|y|$ < 0.1). The measured part…
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 transverse momentum spectra of final-state light flavor particles produced in proton-proton (p-p), copper-copper (Cu-Cu), gold-gold (Au-Au), lead-lead (Pb-Pb), and proton-lead (p-Pb) collisions for different centralities at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) energies are studied in the framework of a multisource thermal model. The experimental data measured by the STAR, CMS, and ALICE Collaborations are consistent with the results calculated by the multi-component Erlang distribution and Tsallis Statistics. The effective temperature and real temperature …
We present an overview of the recent abundant measurements for charm production at RHIC. The significant information of charm cross sections in different collision system at 200 GeV and charmed hadron freeze-out and flow properties extracted from these measurements are presented. The heavy flavor energy loss in the medium and heavy flavor related azimuthal correlations in heavy ion collisions are also discussed.
The study of the multi-strange production in the final state of ultra-relativistic Au+Au collisions at top RHIC energy gives information on the freeze-out conditions and probably on earlier stages of the collision. The chemical freeze-out temperature as well as the strangeness phase space occupancy factor gamma_s extracted from statistical models are studied as a function of the collision centrality. Within the framework of a hydrodynamically-inspired model the transverse collectivity of the collision is investigated. In this view, multi-strange particles seem to develop significant radial tra…
Based on an evaluation of data on pion interferometry and on particle yields at mid-rapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda_f reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from AGS to RHIC.
Predictions of the single-freeze-out model for the particle spectra at RHIC are presented. The model assumes that the chemical and thermal freeze-outs occur simultaneously, and incorporates in simple terms the longitudinal and transverse flow. All resonance decays are included. The model predictions and the data are in striking agreement in the whole available range of momenta.
Using an analytical parameterization of hadronic freeze-out in relativistic heavy ion collisions, we present a detailed study of the connections between features of the freeze-out configuration and physical observables. We focus especially on anisotropic freeze-out configurations (expected in general for collisions at finite impact parameter), azimuthally-sensitive HBT interferometry, and final-state interactions between non-identical particles. Model calculations are compared with data taken in the first year of running at RHIC; while not perfect, good agreement is found, raising the hope tha…
Measurements of a variety of hadron species in Au+Au collisions at 200 GeV by the STAR experiment are used to investigate properties of such collisions. We present a study of particle yields and transverse momentum spectra within the framework of chemical and local kinetic equilibrium models. The extracted freeze-out properties are studied as function of collision centrality. Those properties together with inferred initial conditions provide insights about collision dynamics at RHIC.
A current focus at RHIC is the Beam Energy Scan to study the QCD phase diagram -- temperature ($T$) vs. baryon chemical potential ($μ_{B}$). The STAR experiment has collected data for Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7 GeV, 11.5 GeV, and 39 GeV in the year 2010. We present midrapidity results on rapidity density, average transverse mass, and particle ratios for identified hadrons from the STAR experiment. Collision dynamics are studied in the framework of chemical and kinetic freeze-out conditions.
I present fits with the so-called blast-wave model to single-particle spectra and HBT correlations from Au+Au collisions at a CMS energy of 130 AGeV. There is only little choice of freeze-out temperature and transverse flow velocity for which the model fits both the identified spectra and the correlation radii just well enough not to be excluded. The observed steep M_t dependence of R_side leads to a temperature which it is problematic to interpret. The applicability of the model for the freeze-out description is thus questioned.
We present predictions for the formation of (anti)nuclear bound states in nucleus-nucleus reactions at RHIC energies. he phase space coalescence method is used in combination with RQMD-v2.4 transport calculations to demonstrate the relevance of particle production as well as the longitudinal and transverse flow components. The formation of deuterons follows an approximate scaling law proportional to the relative freeze-out densities of nucleons and produced secondaries. For antideuterons, an additional suppression appears that is proportional to the number of nucleons, pointing toward multiple…
The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) σ-ωapproach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three…
We analyze the transverse momentum distribution of $J/ψ$ mesons produced in Au + Au collisions at the top RHIC energy within a blast-wave model that accounts for a possible inhomogeneity of the charmonium distribution and/or flow fluctuations. The results imply that the transverse momentum spectra of$J/ψ$, $ϕ$ and $Ω$ hadrons measured at the RHIC can be described well if kinetic freeze-out takes place just after chemical freeze-out for these particles.
Pion interferometry ("HBT") measurements relative to the reaction plane provide an estimate of the transverse source anisotropy at freeze-out, which probes the system dynamics and evolution duration. Measurements by the STAR Collaboration indicate that the source is extended increasingly out-of-plane with increasing impact parameter, suggesting a short evolution duration roughly consistent with estimates based on azimuthally-integrated HBT measurements.
In this presentation, I discussed a) the charm total cross-section and its comparisons to measurements at other beam energies and pQCD calculations; b) the semileptonic decay of charmed hadrons and the sensitivity of non-photonic leptons to charm quark collective flow and freeze-out; c) semileptonic decayed electron spectrum at high transverse momentum, its comparison to FONLL in p+p and d+Au collisions, and heavy-quark energy loss in Au+Au collisions.
Recents experimental findings on the properties of the chemical and kinetic freeze-out are reviewed, including data from low energies (SPS) over RHIC, up to recent results from the LHC. We discuss whether chemical freeze-out coincides with hadronization or if there is evidence for a "life after hadronization" which might significantly change particle abundances.
In this report, we discuss the measurement of the hadronic decay modes of resonances in relativistic heavy-ion collisions, emphasizing on RHIC results. The study of resonances can provide: (1) the yield and spectra of more particles with different properties to study whether the system is in thermal equilibrium; (2) an independent probe of the time evolution of the source from chemical to kinetic freeze-out and detailed information on hadronic interaction at later stage; (3) the study of medium effects at late stages of the collisions; (4) a measurement of flavor and baryon/meson dependence of…
The first measurements of light antinucleus production in Au+Au collisions at RHIC are reported. The observed production rates for antideuterons and antihelions are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at SPS energy. These analyses also indicate that the antihelion freeze-out volume is smaller than the antideuteron freeze-out volume.
Identified hadron spectra and ratios provide a unique tool to study the bulk particle production in heavy-ion collisions and explore the QCD phase diagram. In these proceedings we present the analysis of charged pion, kaon and (anti)proton distributions from sqrt(s_NN)=200 and 62.4 GeV Cu+Cu collisions, collected by the STAR experiment. New measurements extend the systematic studies of bulk properties, addressing the energy and the system size dependence of freeze-out parameters at RHIC. The available centrality selection of Cu+Cu data bridge the gap between the smaller d+Au and larger Au+Au s…
The resonance production of $Δ$, K(892), $Σ$(1385), $Λ$(1520) and $ϕ$ from elementary p+p and Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 200 GeV from the STAR experiment at RHIC is presented. Yields and spectra are discussed in terms of chemical and thermal freeze-out conditions. Thermal models do not describe sufficiently the yields of the resonance production in central Au+Au collisions. The approach which includes pseudo-elastic and elastic hadronic interactions after chemical freeze-out until thermal freeze-out suggests a time span of $Δτ>$5 fm/c.
The rapidity and centrality dependence of baryon to meson ratios in Au$+$Au, Cu$+$Cu and p$+$p collisions at $\sqrt{s_{NN}}$ = 200 GeV at RHIC is presented. The $\bar{p}/π^{-}$ ratios are founded to be independent of collision system at a fixed $<N_{part}>$ at mid- and forward rapidities.
We study charge fluctuations within the statistical hadronization model. Considering both the particle yield ratios and the charge fluctuations we show that it is possible to differentiate between chemical equilibrium and non-equilibrium freeze-out conditions. As an example of the procedure we show quantitatively how the relative yield ratio $Λ/K^-$ together with the normalized net charge fluctuation $v(Q)=\ave{ΔQ^2}/\ave{\Nch}$ constrain the chemical conditions at freeze-out. We also discuss the influence of the limited detector acceptance on fluctuation measurements, and show how this can be…
A nontrivial space-time structure of the hot system created at RHIC is the defining aspect of the physics of relativistic heavy ion collisions. Femtoscopy through pion intensity interferometry provides direct access to the dynamic geometric substructure of the freeze-out stage, and appears to confirm source evolution via collective flow. Since flow is usually considered to be a bulk phenomenon, it is surpring to find a simple scaling in preliminary HBT radii from p+p, d+Au and Au+Au collisions. Investigating the light system data in detail, we discuss a new way to visualize the ``fine structur…
The transverse momentum distributions of the identified particles produced in small collision systems at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) have been analyzed by four models. The first two models utilize the blast-wave model with different statistics. The last two models employ certain linear correspondences based on different distributions. The four models describe the experimental data measured by the Pioneering High Energy Nuclear Interaction eXperiment (PHENIX), Solenoidal Tracker at RHIC (STAR), and A Large Ion Collider Experiment (ALICE) cCollabora…
We compute v4/(v2)^2 in ideal and viscous hydrodynamics. We investigate its sensitivity to details of the hydrodynamic model and compare the results to experimental data from RHIC. Whereas v2 has a significant sensitivity only to initial eccentricity and viscosity while being insensitive to freeze out temperature, we find that v4/(v2)^2 is quite insensitive to initial eccentricity. On the other hand, it can still be sensitive to shear viscosity in addition to freeze out temperature, although viscous effects do not universally increase v4/(v2)^2 as originally predicted. Consistent with data, we…
We study the chemical freeze-out dynamics of strange particles ($K,\, Λ,\, Σ$) from a homogeneous and isotropically expanding hadronic system of $π, K, ρ, N, Λ$ and $Σ$ with zero net baryon density. We use the momentum integrated Boltzmann equation and study their evolution over the bulk hadronic matter, a condition being similar to the one created at top RHIC and LHC energies. The cross-sections, which are input to the equations, are taken either from phenomenological models or parameterized by comparing against experimental data. From this microscopic calculation we find that these strange p…
The pseudorapidity densities of transverse energy, the charged particle multiplicity and their ratios, $E_T/N_{ch}$, are estimated at mid-rapidity, in a statistical-thermal model based on chemical freeze-out criteria, for a wide range of energies from GSI-AGS-SPS to RHIC. It has been observed that in nucleus-nucleus collisions, $E_T/N_{ch}$ increases rapidly with beam energy and remains approximately constant at about a value of 800 MeV for beam energies from SPS to RHIC. $E_T/N_{ch}$ has been observed to be almost independent of centrality at all measured energies. The statistical-thermal mod…
A QCD phase transition may reflect in a inhomogeneous decoupling surface of hadrons produced in relativistic heavy-ion collisions. We show that due to the non-linear dependence of the particle densities on the temperature and baryon-chemical potential such inhomogeneities should be visible even in the integrated, inclusive abundances. We analyze experimental data from Pb+Pb collisions at CERN-SPS and Au+Au collisions at BNL-RHIC to determine the amplitude of inhomogeneities.
I will describe the latest results from lattice QCD pertaining to a potential flavour hierarchy in the hadronic freeze-out from the QCD crossover region. I will compare these results to a variety of improved hadronic resonance gas calculations and to experimental data of fluctuations of net-charge, net-proton and net-kaon multiplicity distributions, which serve as a proxy for the susceptibilities of conserved quantum numbers on the lattice. I will conclude that there is intriguing evidence for a flavour dependent freeze-out, and I will suggest expansions to the experimental program at RHIC and…
Transverse momentum spectra of negative and positive pions produced at mid-(pseudo)rapidity in inelastic or non-single-diffractive proton-proton collisions and in central nucleus-nucleus collisions over an energy range from a few GeV to above 10 TeV are analyzed by a (two-component) blast-wave model with Boltzmann-Gibbs statistics and with Tsallis statistics respectively. The model results are in similarly well agreement with the experimental data measured by a few productive collaborations who work at the Heavy Ion Synchrotron (SIS), Super Proton Synchrotron (SPS), Relativistic Heavy Ion Coll…
The STAR experiment at RHIC has a unique capability of measuring identified hadrons over a wide range of pseudorapidity ($η$), transverse momentum ($p_{T}$), and azimuthal angle ($ϕ$) acceptance. The data collected ($\sqrt{s_{NN}}$ = 7.7, 11.5, and 39 GeV) in its beam energy scan (BES) program provide a chance to investigate the final hadronic state freeze-out conditions of ultrarelativistic Au+Au collisions. The particle ratios are used to compare to a statistical model calculation using both grand canonical and strangeness canonical ensembles to extract the chemical freeze-out parameters. Th…
High-energy collisions of heavy ions provide a means to study QCD in a regime of high parton density, and may provide insight into its phase structure. Results from the four experiments at RHIC (BRAHMS, PHENIX, PHOBOS and STAR) are presented, and placed in context with the lower energy data from the AGS and SPS accelerators. The focus is on the insights these measurements provide into the time history of the collision process. Taken together, the data point to the creation of a deconfined state of matter that forms quickly, expands rapidly and freezes out suddenly.
We present the first measurements of the transverse momentum spectra and azimuthal anisotropy of the identified hadrons ($π^{+}$, $π^{-}$, $K^{+}$, $K^{-}$, $p(\bar{p})$, $K^{0}_{s}$, $Λ(\barΛ)$ and $ϕ$) at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5 GeV for various collision centralities. These measurements are compared to corresponding results from other BES energies. The bulk properties of the system, like the chemical and kinetic freeze-out conditions and the collectivity extracted from the measured yields of the produced particles are presented. The difference between baryo…
