The BRAHMS measurement of proton-to-pion ratios in Au+Au and p+p collisions at 62.4 and 200 GeV is presented as a function of transverse momentum and collision centrality within the pseudorapidity range 0 < eta < 3.2. The p/pi ratio measured for Au+Au system at 62.4 GeV, eta = 3.2 reaches astounding value of 8-10 at pT >= 1.5 GeV/c. For these energy and pseudorapidity interval no centrality dependency of p/pi ratio is observed. The baryon-to-meson ratio of nucleus-nucleus data are consistent with results obtained for p+p interactions.
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.
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 will present a review of selected results on strange baryon production from nucleus-nucleus collisions at the AGS, SPS and RHIC. From the AGS and SPS heavy ion physics program several intriguing aspects: centrality dependence of strangeness production, anti-hyperon yield, hyperon production enhancement and baryon number transport will be highlighted. Our discussion on RHIC results will focus on experimental probes of partonic degree of freedom. Measurements of the elliptic flow v2 and the nuclear modification factor and their distinctive particle dependence are presented as a function of tr…
We study the rapidity losses in central heavy-ion collisions from AGS to RHIC energies with the mean rapidity determined from the projectile net-baryon distribution after collisions. The projectile net-baryon distribution in the full rapidity range was obtained by removing the target contribution phenomenologically at forward rapidity region from the experimental net-baryon measurements and taking into account the projectile contribution at backward rapidity region. Based on the full projectile net-baryon distributions, calculation results show that the rapidity loss stops increasing from the …
Particle correlations at small relative velocities can be used to study the space-time evolution of hot and expanding system created in heavy ion collisions. Baryon and antibaryon source sizes extracted from baryon-baryon correlations complement the information deduced from the correlation studies of identical pions. Correlations of non-identical particles are sensitive also to the space-time asymmetry of their emission. High statistics data set of STAR experiment allows us to present the results of baryon-baryon correlation measurements at various centralities and energies, as well as to take…
The baryon production mechanism at the intermediate $p_T$ (2 - 5 GeV/$c$) at RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au systems at RHIC may provide us a further insight on the origin of the baryon anomaly and its evolution as a function of $\sqrt{s_{NN}}$. In 2005 RHIC physics program, the PHENIX experiment accumulated the first intensive low beam energy data in Cu+Cu collisions. We present the preliminary results of identified charged hadron spectra in Cu+Cu at $\sqrt{s_{NN}}$ = 22.5 and 62.4 GeV using the PHENIX detector. The centrality and beam energy de…
We report STAR preliminary results on multi-strange baryon production in Au+Au collisions at sqrt(s_NN)=200 GeV at RHIC. Its implication for the formation of a new state of matter is discussed. The system size dependence on the production of strange baryons is investigated to study the onset of strange quark equilibration in the medium. The nuclear modification factor of Lambda, Xi and Omega is also presented. Its suppression at p_T>3 GeV/c supports the formation of a dense interacting medium at RHIC. The spectra of multi-strange baryons reveal that within a hydro-inspired model, they may deco…
An update on femtoscopic pi-Xi correlations in Au+Au collisions as measured by the STAR experiment at RHIC is presented. Centrality dependence of Gaussian radii and relative emission asymmetry is extracted for the first time.
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…
Experimental results for identified hadron spectra in AA collisions at RHIC are reviewed. Jet suppression in central AuAu collisions at 200 GeV is seen in leading meson and baryon spectra at high p_t. Enhanced baryon production at intermediate p_T (2<p_t<5 GeV/c) is related to quark content but not its mass.In d+Au collisions Cronin enhancement is observed with larger magnitude for baryons than for mesons, but this difference can not explain the baryon-to-meson ratio in Au+Au collisions. In Au+Au the observations at 62.4 GeV and 200 GeV are very similar, but smaller suppresion of the leading p…
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…
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.
Large proton and antiproton enhancement with respect to pions has been observed at intermediate transverse momentum $p_T \approx$ 2-5 GeV/$c$ in Au+Au collisions at RHIC. To investigate the possible source of this anomaly, the production of $ϕ$ mesons and two particle angular correlations triggered by mid-$p_T$ baryons or mesons are studied. We also present the first measurement of proton and antiproton production at $\sqrt{s_{NN}} = 62.4$ GeV in Au+Au collisions, which aims to study the energy dependence of the observed baryon enhancement.
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.
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…
Using the forward time projection chambers of STAR we measure the centrality dependent Lambda and Anti-Lambda yields in d+Au collisions at \sqrt{s_{NN} = 200 GeV at forward and backward rapidities. The contributions of different processes to particle production and baryon transport are probed exploiting the inherent asymmetry of the d+Au system. While the d side appears to be dominated by multiple independent nucleon-nucleon collisions, nuclear effects contribute significantly on the Au side. Using the constraint of baryon number conservation, the rapidity loss of baryons in the incoming deute…
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.
We present a fully three-dimensional initial state model for relativistic heavy-ion collisions at RHIC Beam Energy Scan (BES) collision energies. The initial energy and net baryon density profiles are produced based on a classical string deceleration model. The baryon stopping and fluctuations during this early stage of the collision are investigated by studying the net baryon rapidity distribution and longitudinal decorrelation of the transverse geometry.
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>$5 fm/c.
We measure the relative abundances of strange mesons, baryons, and anti-baryons correlated with high-$p_T$ trigger particles in $^{197}$Au + $^{197}$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Particle yields and ratios are extracted on the near-side and away-side of the trigger particle. The associate-particle ratios are studied as a function of the angle relative to the trigger particle azimuth $Δϕ$. Such studies should help elucidate the origin of the previously observed correlations and their strong modifications in Au+Au collisions relative to p+p collisions. We discuss how these measurem…
We present the recent results of strangeness production at the mid-rapidity in Au + Au collisions at RHIC, from $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV. The $v_2$ of multi-strange baryon $Ω$ and $ϕ$ mesons are similar to that of pions and protons in the intermediate $p_T$ range (2 - 5 GeV/$c$) in $\sqrt{s_{\rm NN}}$ = 200 GeV Au + Au collisions, indicating that the major part of collective flow has been built up at partonic stage. The breaking of mass ordering between $ϕ$ mesons and protons in the low $p_T$ range ($<$ 1 GeV/$c$) is consistent with a picture that $ϕ$ mesons are less sensitive to l…
We present STAR measurements of K^{0}_{S}, ϕ, Λ, Ξ, and Ωat mid-rapidity from Au+Au collisions at \sqrt{s_{NN}} = 7.7, 11.5, 19.6, 27, and 39 GeV from the Beam Energy Scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC). Nuclear modification factors and baryon-to-meson ratios are measured to understand recombination and parton energy loss mechanisms. Implications on partonic versus hadronic dynamics at low beam energies are discussed.
We present the first elliptic flow, $v_{2}$, measurement for the $ϕ$-meson in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. At low $p_{T}$ (<2 GeV/c), the $v_{2}$ is consistent with mass ordering expected from hydrodynamics, while at higher $p_{T}$ (>4 GeV/c), it follows the same trend as the $K^{0}_{S}$ $v_{2}$ and a parameterization for number of quarks = 2. The nuclear modification factor, $R_{CP}$, has also been measured and it follows the same trend as the $K^{0}_{S}$ rather than the $Λ$ which confirms the baryon/meson-type dependence of $R_{CP}$ at RHIC. A model based on the recombination…
Flow measurements of multi-strange baryons from Au + Au collisions at RHIC energies demonstrate that collectivity develops before hadronization, among partons. To pin down the partonic EOS of matter produced at RHIC, the status of thermalization in such collisions has to be addressed. We propose to measure collective flow of heavy-flavor quarks, e.g. charm quarks, as an indicator of thermalization of light flavors ($u,d,s$). The completion of the time of flight barrel and the proposed upgrade with a $μ$Vertex detector for heavy-flavor identification in STAR are well suited for achieving these …
Using a hybrid (viscous hydrodynamics + hadronic cascade) framework, we model the bulk dynamical evolution of relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan (BES) collision energies, including the effects from non-zero net baryon current and its dissipative diffusion. This framework is in full (3+1)D, which allows us to study the non-trivial longitudinal structure and dynamics of the collision systems, for example baryon stopping and transport, as well as longitudinal fluctuations. For the first time, the quantitative effect of net-baryon diffusion…
Due to its large acceptance, the STAR experiment has acquired a wealth of data on strangeness production for a variety of collisions systems and energies, from p+p to Au+Au. By using the yields and spectra, we address the evolution of the bulk system, including strangeness enhancement and the flavour dependence of radial and elliptic flow. Utilising the fact that we can identify strange baryons and mesons, we investigate different hadronization mechanisms in the intermediate and high p$_{T}$ regions. The ratios of the particle yields, measured to high p$_{T}$, are used to further investigate t…
The transverse momentum and rapidity distributions of net-baryons (baryons minus anti-baryons) produced in central gold-gold (Au-Au) collisions at 62.4 and 200 GeV are analyzed in the framework of a multisource thermal model. Each source in the model is described by the Tsallis statistics to extract the effective temperature and entropy index from the transverse momentum distribution. The two parameters are used as input to describe the rapidity distribution and to extract the rapidity shift and contribution ratio. Then, the four types of parameters are used to structure some scatter plots of …
We report the measurement of the directed flow ($v_{1}$) for charged kaons in Au+Au collisions at $\sqrt{s_{NN}}$ =7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV as a function of rapidity and compare these results for pions, protons and antiprotons. These new kaon results may help to constrain the medium properties and collision dynamics including the in-medium kaon potential and baryon number transport in these collisions.
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…
The experimental data for identified hadron spectra from pp,d+A and AA collisions are reviewed. Three regions with different dominant production mechanisms are considered: soft region (pt <2 GeV/c) - with large degree of collectivity and thermalization, hard particle production which exhibits jet-quenching in Au+Au collisions at RHIC and intermediate region (2 < pt <5 GeV/c) with distinct baryon dynamics. Cronin effect, nuclear modification factors and jet-like correlations are studied with the goal of understanding the baryon dynamics at RHIC.
Two particle azimuthal correlations with strange trigger particles ($K^0_S,Λ,Ξ$) are presented in Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR at RHIC. The near-side associated yield is investigated as a function of centrality, $p_T$, and strangeness content of the trigger to investigate possible flavour or meson/baryon differences. The system size dependence of both the jet-like correlations and the long range pseudorapidity correlations is studied to give insight into the origin of these two components.
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.
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…
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…
We report new results on $v_2(p_T)$ for Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV for charged hadrons, pions, kaons, (anti)protons, $K^0_s$, and $Λ$. The analysis is extended to $p_T=12$ GeV/c for charged hadrons and $p_T=4$ GeV/c for identified particles. A comparison of the azimuthal anisotropy of charged hadrons measured at \sqrtsNN=130 and 200 GeV is presented. The $p_T$-dependence of baryon versus meson elliptic flow is discussed.
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…
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…
Light nuclei have much smaller binding energy compared to the temperature of the system created in heavy-ion collisions. Consequently, the distributions of light nuclei can be used to probe the freeze-out properties, such as correlation volume and local baryon density of the medium created in high-energy nuclear collisions. In this paper, we report the results of deuteron and anti-deuteron production in Au+Au collision at $\sqrt{s_\mathrm{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by STAR at RHIC. The collision energy, centrality and transverse momentum dependence of th…
The hyperon-hyperon and hyperon-nucleon interactions are important in search for exotic hadrons such dibaryon as a bound state of two baryons. $Λ$-$Λ$ correlation has been measured in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 200 GeV at RHIC-STAR experiment using high statistics data recently taken, which has been found to clearly show the anti-correlation. The first measurements of p-$Ξ$ and $Ξ$-$Ξ$ correlations in Au+Au collisions have been shown. The p-$Ξ$ correlation function shows the strong attractive interaction, which is consistent with HAL QCD calculation. $Ξ$-$Ξ$ correlation has als…
We present the incident energy and system size dependence of the pT spectra for charged pions, protons, and anti-protons using Au+Au and Cu+Cu collisions at Sqrt(sNN) = 62.4 and 200 GeV in STAR experiment at RHIC. Through these measurements in the pT range of 0.2 < pT < 10 GeV/c we conduct a systematic study of the beam energy, system size and particle species dependence of nuclear modification factors and address specific predictions from the quark coalescence models regarding the beam energy dependence of baryon enhancement in the intermediate pT (2 < pT < 6 GeV/c) region.
We present a systematic study of transverse mass spectra ($m_T$) of mesons and baryons at RHIC and LHC energies. In an earlier study, it was shown that all the mesons produced in p+p and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV follow $m_T$ scaling while in Au+Au collisions at same energy the mesons with strange and charm quark contents do not follow $m_T$ scaling which can be attributed to medium modifications. We extend this study for baryons produced in all above colliding systems at $\sqrt{s_{NN}}$ = 200 GeV. Although all available baryon spectra behave differently from mesons but are …
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 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…
In the RHIC Beam Energy Scan program, gold nuclei are collided with different collision energies in the range from few to 62.4 GeV. The goals of the program are to explore the onset of QGP creation, locate the critical point of QCD and study dense baryon matter. We report on the first application of Monte Carlo Glauber (GLISSANDO2) and T$_{\rm R}$ENTo $p=0$ initial states extended to 3D for event-by-event viscous fluid dynamic (vHLLE) with hadronic cascade modelling of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=27$ and 62.4 GeV, which is the upper region of RHIC BES energies. The initial states…
The power-law tail of high-pt pi^\pm spectra observed in forward d+Au collisions at RHIC can be attributed to the power-law decrease of the dipole forward scattering amplitude appearing in the color glass condensate (CGC) approach. Forward particle production probes the small-x gluon distribution of the target nucleus where its anomalous dimension is rather flat (gamma = 0.6 \sim 0.8) for moderately high pt (\lsim 5 GeV), and where the leading-twist DGLAP approximation is not valid. In the same framework, we examine p and \bar{p} production using baryon fragmentation functions parameterized in…
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…
The drag and diffusion coefficients of heavy baryons ($Λ_c$ and $Λ_b$) in the hadronic phase created in the latter stage of the heavy-ion collisions at RHIC and LHC energies have been evaluated recently. In this work we compute some experimental observables, such as the nuclear suppression factor $R_{AA}$ and the elliptic flow $v_2$ of heavy baryons at RHIC and LHC energies, highlighting the role of the hadronic phase contribution to these observables, which are going to be measured at Run 3 of LHC. For the time evolution of the heavy quarks in the QGP and heavy baryons in the hadronic phase w…
The transverse momentum spectra of $π^{-}$, $π^{+}$, $K^{-}$, $K^{+}$, $\bar{p}$, and $p$ produced in Au+Au collisions at center-of-mass energy $\sqrt{s_{NN}}=7.7$, 11.5, 19.6, 27, 39, 62.4, 130, and $200$ GeV are analyzed in the framework of a multisource thermal model. The experimental data measured at midrapidity by the STAR Collaboration are fitted by the (two-component) standard distribution. The effective temperature of emission source increases obviously with the increase of the particle mass and the collision energy. At different collision energies, the chemical potentials of up, down,…
Although strange quarks are produced in $s\bar{s}$ pairs, the ratio of $Ω^{-}$ to ${\barΩ}^{+}$ is greater than one in heavy-ion collisions at lower RHIC energies. Thus the produced $Ω$ hyperons must carry net baryon quantum numbers from the colliding nuclei. We present results of $K$-$Ω$ correlations from AMPT model simulations of Au+Au collisions at $\sqrt{s_{NN}}$ = 14.6 GeV, to probe dynamics for baryon number transport to mid-rapidities at this beam energy. We use both the default and string-melting versions to illustrate how hadronization schemes of quark coalescence and string fragmenta…
Baryon fluctuation signatures of the onset of deconfinement
Jan Kochanowski University（扬·科哈诺夫斯基大学）；Bogolyubov Institute for Theoretical Physics（博戈柳博夫理论物理研究所）；GSI Helmholtzzentrum für Schwerionenforschung（德国重离子研究中心）
We present the inclusive and identified particle (pion, proton and their antiparticle) production in Single Diffraction Dissociation and Central Diffraction processes with the STAR detector at RHIC. The forward-scattered proton(s) are tagged in the STAR Roman Pot system while the charged particle tracks are reconstructed in the STAR Time Projection Chamber. Ionization energy loss and time of flight of charged particles are used for particle identification. In addition, the proton-antiproton production asymmetry as a function of rapidity is measured and used to study the baryon number transfer …
The thermal model of particle production is used to analyze the particle ratios and the p_T spectra measured recently at RHIC. Our fit of the particle ratios yields the temperature at the chemical freeze-out T_chem = 165 +- 7 MeV with the corresponding baryon chemical potential mu^B_chem = 41 +- 5 MeV. The quality of the fit shows that the model works well for RHIC. The p_T spectra are evaluated in an approach which takes into account the modifications of the initial thermal distributions by the secondary decays of resonances. All two- and three-body decays are included. This leads to an effec…
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…
We present the first results using the STAR detector from the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC). In this program, Au ion collisions at center of mass energies (\sqrt{s_{NN}}) of 7.7, 11.5 and 39 GeV allowed RHIC to extend the study of the QCD phase diagram from baryonic chemical potential values of 20 MeV to about 400 MeV. For the high net-baryon density matter at midrapidity, formed in these collisions, we report several interesting measurements. These include the observation of difference between anti-particle and particle elliptic flow, disappearan…
