We report the measurements of proton-deuteron ($p$-$d$) and deuteron-deuteron ($d$-$d$) correlation functions in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 3 GeV using fixed-target mode with the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). For the first time, the source size ($R_{G}$), scattering length ($f_{0}$), and effective range ($d_{0}$) are extracted from the measured correlation functions with a simultaneous fit. The spin-averaged $f_0$ for $p$-$d$ and $d$-$d$ interactions are determined to be -5.28 $\pm$ 0.11(stat.) $\pm$ 0.82(syst.) fm and -2.62 $\pm$ 0.02(stat.) $\pm$ 0.24(syst.) fm, respectively. The measured $p$-$d$ interaction is consistent with theoretical calculations and low-energy scattering experiment results, demonstrating the feasibility of extracting interaction parameters using the femtoscopy technique. The reasonable agreement between the experimental data and the calculations from the transport model indicates that deuteron production in these collisions is primarily governed by nucleon coalescence.
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.
In this paper we present the measurement of charged pion two-particle femtoscopic correlation functions in 200 GeV Au+Au collisions, in 31 average transverse mass bins, separately for positive and negative pion pairs. Lévy-shaped source distributions yield a statistically acceptable description of the measured correlation functions, with three physical parameters: correlation strength parameter lambda, Lévy index alpha and Lévy scale parameter R. The transverse mass dependence of these Lévy parameters is then investigated and their physical interpretation is also discussed, and the appearance …
Charged pion two-particle correlation functions were measured in 0-30% centrality 200 GeV Au+Au collisions with the PHENIX experiment at RHIC. The measured correlation functions can be statistically well described based on the assumption of Levy-shaped source distributions. In this proceedings paper we present the Levy parameters of the measured correlation functions: correlation strength parameter lambda, Levy index alpha and Levy scale parameter R as a function of pair transverse mass mT, in 31 bins from 228 to 871 MeV, separately for positive and negative pion pairs. We discuss the physical…
Femtoscopic measurements at a variety of facilities have established a clear dependence of spatial scales with event multiplicity and particle transverse mass ($m_T$) in heavy ion collisions from $\sqrt(s_{NN}) \sim 2-200 GeV$. The $m_T$-dependence is thought to arise from collective, explosive flow of the system, as probed by independent measurements, while the multiplicity dependence reflects the increased spatial extent of the final state with decreasing impact parameter. Qualitatively similar dependences have been reported from high energy hadron and lepton collisions, where the conceptual…
Azimuthally-sensitive femtoscopy for heavy-ion collisions at RHIC and LHC is explored within the approach consisting of the hydrodynamics of perfect fluid followed by statistical hadronization. It is found that for the RHIC initial conditions the very same framework that reproduces the standard soft observables (including the transverse-momentum spectra, the elliptic flow, and the azimuthally-averaged HBT radii) leads to a proper description of the azimuthally-sensitive femtoscopic observables - we find that the azimuthal variation of the side and out HBT radii is very well reproduced for all …
The $m_T$-dependencies of the femto-scales, the so-called interferometry and source radii, are investigated within the hydrokinetic model for different types of particle pairs - pion-pion, kaon-kaon, proton-proton and proton-lambda, - produced in Pb+Pb and $p+p$ collisions at the LHC. In particular, such property of the femto-scales momentum behavior as $m_T$-scaling is studied for the systems with (w) and without (w/o) intensive transverse flow, and also w and w/o re-scattering at the final afterburner stage of the matter evolution. The detail spatiotemporal description obtained within hydrok…
We present femtoscopic results for proton and Lambda correlation functions measured by ALICE in sqrt(sNN) = 2.76 TeV Pb-Pb collisions. Femtoscopic radii are extracted from pp, pbarpbar, and ppbar pairs. Comparisons of these radii with those from pion and kaon analyses reveal an approximate transverse mass scaling that is consistent with explanations of radial flow. Inelastic final state interactions are explored in baryon-antibaryon correlations functions to investigate their relationship with reduced proton yields at LHC energies.
In this report, femtoscopic measurements with proton-proton, antiproton-antiproton, proton-antiproton, proton-antilambda, antiproton-lambda and lambda-antilambda pairs in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV registered by ALICE at the LHC are presented. Emission source sizes extracted from the correlation analysis with (anti)protons grow with the event multiplicity, as expected. A method to extract the interaction potentials (e.g. for proton-antilambda and antiproton-lambda pairs) based on femtoscopy analysis is discussed. The importance of taking into account the so-called residual correla…
The longitudinal proton-proton femtoscopy (HBT) correlation function, based on the idea that in a heavy ion collision at $\sqrt{s} \lesssim 20$ GeV stopped protons are likely to be separated in configuration space, is evaluated. It shows a characteristic oscillation which appears sufficiently pronounced to be accessible in experiment. The proposed measurement is essential for estimating the baryon density in the central rapidity region, and can be also viewed as an (almost) direct verification of the Lorentz contraction of the fast-moving nucleus.
Femtoscopy is a technique enabling measurements of the space-time characteristics of particle-emitting sources. However, the femtoscopic analysis is also sensitive to the interaction cross-section. In this paper we show the first preliminary measurements of $\rm K^0_SK^{\pm}$ correlation functions in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. These correlations originate from the final-state interactions which proceed through the $a_0(980)$ resonance only and can be employed to constrain its parameters. A similar approach can be applied to baryon pairs to extract the unknown interaction…
We present results of femtoscopic analysis with K0s-K0s, Kch-Kch, p-p, pbar-pbar, p-pbar and lambda-antilambda in Pb-Pb collisions at sqrt{s_NN}=2.76 TeV and K0s-K0s in pp collisions at sqrt{s}=7 TeV registered by ALICE at the LHC. The femtoscopic radius is extracted from the one-dimensional correlation functions. The analysis reveals that the emission source sizes of pions, kaons and protons measured in heavy-ion collisions exhibit approximate transverse mass scaling which is consistent with hydrodynamic collectivity prediction. Furthermore, baryon-antibaryon correlations are investigated to …
Analyses of two-particle correlations have provided the chief means for determining spatio-temporal characteristics of relativistic heavy ion collisions. We discuss the theoretical formalism behind these studies and the experimental methods used in carrying them out. Recent results from RHIC are put into context in a systematic review of correlation measurements performed over the past two decades. The current understanding of these results is discussed in terms of model comparisons and overall trends.
In these proceedings, we present the measurements of proton, light nuclei, and strange particle with neutral kaons correlation functions in Au+Au collisions at the BES program and top RHIC energy. The experimental results will be compared with model calculations to extract the size of emitting source and the properties of final state interactions. The collision energy and centrality dependence of the source size will be studied. Further, the implications for the production mechanism of light nuclei will be discussed.
We report on the results of femtoscopic analysis of Pb-Pb collisions at sqrt(s_NN)=2.76 TeV and pp collisions at sqrt(s)=0.9, 2.76 and 7 TeV with identical pions and kaons. Detailed femtoscopy studies in heavy-ion collisions at SPS and RHIC have shown that emission region sizes ("HBT radii") decrease with increasing pair transverse momentum k_T, which is understood as a manifestation of the collective behavior of matter. The trend was predicted to persist at the LHC. The data from Pb-Pb collisions confirm the existence of a flowing medium and provide strict constraints on the dynamical models.…
Femtoscopy of non-central heavy ion collisions provides access to information on the geometry of the effective pion-emitting source. In particular, the source shape can be studied by measuring femtoscopic radii as a function of the pion emission angle relative to the collision symmetry planes. We present the results of azimuthally differential femtoscopy of Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV at the LHC relative to the second harmonic event plane. We observe a clear oscillation of the extracted radii as a function of the emission angle. We find that $R_{side}$ and $R_{out}$ oscillate …
We present a new event generator based on the three-fluid hydrodynamics (3FH) approach, followed by a particlization at the hydrodynamic decoupling surface and a subsequent UrQMD afterburner stage based on the microscopic UrQMD transport model that accounts for hadronic final state interactions. First results for Au+Au collisions are presented. The following topics are addressed: the directed flow, transverse-mass spectra, as well as rapidity distributions of protons, pions and kaons for two model equations of state, one with a first-order phase transition, the other with a crossover transitio…
The results on the main bulk observables obtained in the simulations within the integrated hydrokinetic model (iHKM) of Au+Au collisions at the RHIC energy $\sqrt{s_{NN}}=200$ GeV are presented along with the corresponding experimental data from the STAR and the PHENIX collaborations. The simulations include all the stages of the collision process: formation of the initial state, its gradual thermalization and hydrodynamization, viscous relativistic hydro-evolution, system's hadronization and particlization, and, finally, an expansion of the interacting hadron-resonance gas. The model gives a …
Ultra-relativistic gold-gold and proton-proton collisions are investigated in the experiments of the Relativistic Heavy Ion Collider (RHIC). In the last several years large amount of results were revealed about the matter created in these collisions. The latest PHENIX results for femtoscopy and correlations are reviewed in this paper. Bose-Einstein correlations of charged kaons in 200 GeV Au+Au collisions and of charged pions in 200 GeV p+p collisions are shown. They are both compatible with previous measurements of charged pions in gold-gold collisions, with respect to transverse mass or numb…
We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-$Λ$ and $Λ$-$Λ$, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at $\sqrt{s}$ = 7 TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented.…
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 present the first azimuthally differential measurements of the pion source size relative to the second harmonic event plane in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of $\sqrt{s_{\rm NN}}=2.76$ TeV. The measurements have been performed in the centrality range 0-50% and for pion pair transverse momenta $0.2 < k_{\rm T} < 0.7$ GeV/$c$. We find that the $R_{\rm side}$ and $R_{\rm out}$ radii, which characterize the pion source size in the directions perpendicular and parallel to the pion transverse momentum, oscillate out of phase, similar to what was observed at …
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.
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…
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…
Exploration of the rich structure of the QCD phase diagram is an important topic in the RHIC heavy ion program. One of the ultimate goals of this program is to search for the critical endpoint. Investigation of the space-time structure of hadron emissions at various phase transition points using Bose-Einstein correlations of identical bosons may provide insight on the location of the critical endpoint. PHENIX has performed comprehensive measurements of the Bose-Einstein correlation in Au+Au collisions at sqrt(sNN) = 15, 19, 27, 39, 62.4, and 200 GeV, where we incorporated Levy-type source func…
Two-particle femtoscopy reveals the space-time substructure of the freeze-out configuration from heavy ion collisions. Detailed fingerprints of bulk collectivity are evident in space-momentum correlations, which have been systematically measured as a function of particle type, three-momentum, and collision conditions. A clear scenario, dominated by hydrodynamic-type flow emerges. Reproducing the strength and features of the femtoscopic signals in models involves important physical quantities like the Equation of State, as well as less fundamental technical details. An interesting approximate "…
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…
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…
Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in relativistic heavy-ion collisions to probe the QCD phase transition and search for the QCD critical point. In this paper, we review the experimental measurements of the cumulants (up to fourth order) of event-by-event net-proton (proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}}=7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, 200$ GeV from the first phase of beam energy scan program at the Relat…
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 …
Via the study of strange particle production within the STAR experiment, we try to address the surprising amount of baryon transport at the Relativistic Heavy Ion Collider (RHIC). We report here preliminary results showing that, at mid-rapidity and for the top energy of RHIC, the number of created baryons exceeds the number transported from the colliding nuclei. However, thanks to the large acceptance of the experimental setup, one could expect to observe the transition between the ``soft'' regime (low transverse momentum -$\pt$- region corresponding to a bulk of hot and dense matter hadronizi…
Evolution of the elliptic flow of hadrons in heavy-ion collisions at RHIC energies is studied within the microscopic quark-gluon string model. The elliptic flow is shown to have a multi-component structure caused by (i) rescattering and (ii) absorption processes in spatially asymmetric medium. Together with different freeze-out dynamics of mesons and baryons, these processes lead to the following trend in the flow formation: the later the mesons are frozen, the weaker their elliptic flow, whereas baryon fraction develops stronger elliptic flow during the late stages of the fireball evolution. …
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 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 …
Multi-strange baryon azimuthal correlations were observed in d+Au and Au+Au data taken by the STAR detector at RHIC. We extract the same-side per-trigger yields for a variety of strange particle species and trigger pt, but do not observe any species dependence. We also report the observation of an elongation in the Delta-eta; direction of the Xi correlation peak, the ridge. Comparing the same-side yields in d+Au and Au+Au data, we conclude that the same-side yield of the azimuthal-only Xi correlations is greatly enhanced by the ridge yield. We also report the first observation of a strong same…
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…
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…
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…
We present results on two-particle azimuthal correlations of high-$p_T$ neutral strange baryons ($Λ$,$\barΛ$) and mesons ($K^0_S$) associated with non-identified charged particles in d+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. In particular, we discuss properties of the near-side yield of associated charged particles as a function of centrality, transverse momentum and $z_T$, as well as possible baryon/meson and particle/antiparticle differences. The results are compared to the proton and pion triggered correlations and to fragmentation and recombination models.
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 results on two-particle correlations using singly-strange particles ($Λ$, $\barΛ$, $K^0_S$) and charged hadrons at intermediate p_T in d+Au and Au+Au collisions at RHIC. We discuss properties of the near-side correlation peak in both azimuthal and pseudo-rapidity space and separate jet-like contributions from the long-range pseudo-rapidity correlations (the ridge). In particular, we study the centrality and p_T dependence of the jet and ridge yields for various trigger and associated particle species and compare the results to model predictions.
