We present the results on measurement of event-by-event pt fluctuations and correlations for Cu+Cu collisions at sqrt{sNN} = 62.4 and 200 GeV from STAR experiment at RHIC. These results are compared with those from Au+Au collisions at sqrt{sNN} = 62.4 and 200 GeV to study the system size dependence. We find that the dynamical pt fluctuations are finite and decrease with increasing collision centrality. The pt correlations are studied as a function of collision centrality and are observed to decrease as we go from peripheral to central collisions. The square root of pt correlations scaled by mean pt are observed to be independent of beam energy as well as colliding ion size.
A new era has started in the field of relativistic heavy-ion physics with lead beams delivered by the Large Hadron Collider (LHC) in November 2010. In this proceedings I highlight the main results from experimental measurements with Pb-Pb collisions at the incident energy of 2.76 TeV/nucleon recorded by the LHC experiments. Recent experimental developments from the Relativistic Heavy Ion Collider (RHIC) at the GeV incident energy scale are also discussed. All together LHC and RHIC measurements provide new insights on the properties and features of the new hot and dense form of matter created i…
Main characteristics of the charged particle dN_ch/deta and transverse energy dE_T/deta production measured in Heavy Ion collisions at RHIC energies are presented in this article. Transformation of the pseudo-rapidity shape, relation to the incident energy and centrality profile are described in a systematic way. Centrality profile is shown to be closely bound to the number of nucleons participating in the collisions, at the same time an alternative approach to study the centrality behavior is also discussed.
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 present the centrality dependence of the $N(Ω)/N(ϕ)$ ratios and $ϕ$ $v_{2}$ measured in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV by the STAR experiment at RHIC. The results are compared to measurements of other identified particles and recombination model expectations in order to gain insight into the partonic collectivity and possible thermalization of the produced medium.
We present a system size and energy dependence of $ϕ$ meson production in Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV and 200 GeV measured by the STAR experiment at RHIC. We find that the number of participant scaled $ϕ$ meson yields in heavy ion collisions over that of p+p collisions are larger than 1 and increase with collision energy. We compare the results with those of open-strange particles and discuss the physics implication.
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 study of the energy dependence of $p_t$ angular correlations inferred from event-wise mean transverse momentum $<p_{t} >$ fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure suggests that the principal source of $p_t$ correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with …
This paper describes the measurement of the energy dependence of elliptic flow for charged particles in Au+Au collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of $\sqrt{s_{_{NN}}} =$ 19.6, 62.4, 130 and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of $η'=|η|-y_{beam}$, scale with approximate linearity throughout $η'$, implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.
We present the centrality dependence of Lambda and Anti-Lambda hyperon global polarization in Au+Au collisions at sqrt{s_NN}=62 GeV and 200 GeV measured with the STAR detector at RHIC. Within the precision of the measurement, we observe no centrality dependence of Lambda and Anti-Lambda hyperon global polarization and within our acceptance it is consistent with zero. Different sources of systematic uncertainties (feed down effects, spin precession) are discussed and estimated. The obtained upper limit, |P_{Lambda,Anti-Lambda}| < 0.02, is compared to theoretical predictions discussed recently i…
PHENIX has measured high transverse momentum (pT) identified hadrons in different collision species and energies in the last five RHIC runs. The systematic study of the high pT hadron production provides an idea on interaction of hard scattered partons and the matter created in relativistic heavy ion collision. The eta/pi0 ratio is measured in Au+Au collisions, which gives a hint on the system thermalization and particle production. A future measurement of hadron and photon measurement is discussed.
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.
Recent STAR measurements of the anisotropic flow coefficients (v$_{n}$) are presented for Au+Au collisions spanning the beam energy range $\sqrt{s_{NN}} = 7.7 - 200$ GeV. The measurements indicate dependences on the harmonic number ($n$), transverse momentum ($p_T$), pseudorapidity ($η$), collision centrality and beam energy ($\sqrt{s_{NN}}$) which could serve as important constraints to test different initial-state models and to aid precision extraction of the temperature dependence of the specific shear viscosity.
Two-particle high-$p_T$ triggered correlations in $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}$ = 62 $GeV$ and $\sqrt{s_{NN}}$ = 200 $GeV$ in STAR at RHIC are presented. The $N_{part}$, $p_T^{associated}$, and $p_T^{trigger}$ dependence of the yield per trigger in the \textit{Jet} and \textit{Ridge} components of the near-side is investigated for h, $K^0_S$, $Λ$, and $Ξ$ trigger and associated particles. The system and energy dependence of these components is a potentially powerful tool to distinguish between models used to describe their production.
The measured elliptic flow (v2) of identified particles as a function of pT and centrality at RHIC suggests the created medium in Au+Au collisions achieves early local thermal equilibrium that is followed by hydrodynamic expansion. It is not known if the eta dependence on v2 is a general feature of elliptic flow or reflects other changes in the particle spectra in going from mid-rapidity to foward rapidities. The BRAHMS experiment provides a unique capability compared to the other RHIC experiments to measure v2 for identified particles over a wide rapidity range. From Run 4 Au+Au collision at …
We report on measurements of directed flow as a function of pseudorapidity in Au+Au collisions at energies of $\sqrt{s_{_{NN}}} =$ 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.
Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity in Pb+Pb collisions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-}, by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV. The modification factor R_{AA} shows a rapid increase with transverse momentum in the covered region. The modification factors R_{AA/pA} and R_{CP} shows a saturation well below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200 GeV RHIC results closely in the…
The energy and system size dependence of pseudorapidity ($η$) and multiplicity distributions of photons are measured in the region -2.3 $\leq$ $η$ $\leq$ -3.7 for Cu + Cu collisions at $\sqrt{s_{NN}}$ = 200 and 62.4 GeV. Photon multiplicity measurements at forward rapidity have been carried out using a Photon Multiplicity Detector (PMD) in the STAR experiment. Photons are found to follow longitudinal scaling for Cu + Cu collisions for 0-10% centrality. A Comparison of pseudorapidity distributions with HIIJING model is also presented.
We present transverse momentum spectra from d+Au collisions at sqrt(s_NN) = 200 GeV for identified hadrons at mid-rapidity and unidentified hadrons in the forward rapidity region using the Solenoidal Tracker at RHIC. We scale these spectra by the mean number of binary collisions to form a transverse momentum dependent ratio to spectra from p+p collisions, showing that the Cronin effect measured at lower centre-of-mass energies is also present at this higher energy. The data also suggest a dependence of the Cronin effect on the hadron species. We also compare central d+Au collisions to more per…
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.
Medium modification of particle spectra and the origin of collectivity in small collision systems are widely debated topics in the heavy-ion community. To address these open questions, we propose the study of particle production and collectivity for varying system sizes,Au+Au $>$ Ru+Ru/Zr+Zr $>$ Cu+Cu $>$ d+Au $>$ $γ$+Au, available at RHIC using the STAR detector. We present the first measurements of centrality dependent charged hadron production in Isobar (Ru+Ru and Zr+Zr) collisions, including the nuclear modification factors ($R_\mathrm{AA}$) at high transverse momentom ($p_\mathrm{T}$), an…
The balance function, which measures the correlation between opposite sign charge pairs, is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. The study of the balance function can provide information about charge creation time as well as the subsequent collective behavior of particles. In this paper, we present a reaction-plane-dependent balance function study for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV and compare with results from recent three particle correlation measurements. We also report balance functions for relati…
The non-Abelian feature of quantum chromodynamics (QCD) results in the gluons losing more energy than quarks in the medium formed in high energy heavy-ion collisions. Experimental results in p+p collisions when compared to NLO pQCD calculations show that at high transverse momentum (pT) the produced protons+anti-protons are dominantly from gluon jets and charged pions have substantial contribution from quark jets. If such a scenario is applied to heavy-ion collisions at RHIC, one would expect the difference in quark and gluon energy loss to have an effect on measured observables, such as high …
The BRAHMS experiment at RHIC has measured the production of charged hadrons as a function of pseudorapidity and transverse momentum in Au+Au, d+Au and p+p collisions at a common energy of sqrt(s_NN)=200GeV, and from these spectra we construct the nuclear modification factors for both ``hot'' and ``cold'' nuclear matter. In this contribution I will show how these factors evolve with pseudorapidity and collision centrality. We see a Cronin-like enhancement in d+Au collisions at midrapidity, going to a strong suppression at eta >= 2. In central Au+Au collisions we find a suppression both at mid-…
Strange particle production is an important experimental observable that allows the study of the strongly interacting matter created in relativistic heavy-ion collisions. The STAR experiment at RHIC has a unique capability of measuring identified strange particles over a wide range of acceptance providing a rich set of data to perform a systematic study. In addition to the data from Au+Au collisions, strange particles from p+p and d+Au collisions are also available for comparison and normalization. A new set of data from Cu+Cu reactions at 62 GeV and 200 GeV provides the chance to compare the …
PHOBOS measurements of elliptic flow are presented as a function of pseudorapidity, centrality, transverse momentum, energy and nuclear species. The elliptic flow in Cu-Cu is surprisingly large, particularly for the most central events. After scaling out the geometry through the use of an alternative form of eccentricity, called the participant eccentricity, which accounts for nucleon position fluctuations in the colliding nuclei, the relative magnitude of the elliptic flow in the Cu-Cu system is qualitatively similar to that measured in the Au-Au system.
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 a…
This paper presents $v_{4}/v_{2}^2$ ratio as a function of transverse momentum ($p_{t}$), pseudorapidity ($η$) and collision centrality in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). It is found that $v_{4}/v_{2}^2$ is larger than Hydrodynamic calculations, the centrality and transverse dependence of this ratio can not be fully described by Hydrodynamics, and the pseudorapidity dependence is opposite to what one expects from Hydrodynamics. The $p_{t}$ dependence of $v_{1}$ is also presented. It is found that $v_{1}(p_{t})…
Elliptic flow has been measured by the BRAHMS experiment as a function of transverse momentum and pseudorapidity for the Au+Au reaction at sqrt[s_{NN}] = 200 GeV. Identified-particle v2 (eta, pt) values were obtained with the two BRAHMS spectrometers at pseudorapidities eta approximately equal to 0, 1, and 3.4. The results show that the differential v2(eta, pt) values for a given particle type are essentially constant over the covered pseudorapidity range. It is suggested that the dominant cause of the observed fall-off of the integral v2 values going away from mid-rapidity is a corresponding …
The transverse momentum ($p_{\rm T}$) and centrality dependence of the azimuthal anisotropy ($v_{2}$) are measured for charged hadrons in different energies and collision species by the PHENIX experiment at RHIC. We find that $v_{2}$ divided by the participant eccentricity of the initial geometry proportionally increases with the number of participants to the 1/3 power except at small $N_{\rm part}$ in Cu+Cu at $\sqrt{s_{\rm NN}}$ = 62.4 GeV. Taking the eccentricity and quark number scaling into account, there is a universal scaling for $v_{2}$ with different energies and collision sizes. The …
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime. The question is whether the signatures proposed for the discovery of a phase transition from hadronic matter to a Quark Gluon Plasma (QGP), that were established on the basis of collisions at the BEVALAC, the AGS, and the SPS, respectively, are still useful and detectable at these high incident energies. In the past two decades, measurements related to strangeness formation in the collision were advocated as potential signatures and were teste…
$J/ψ$ production has been measured in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) during 2004 and 2005, respectively, at mid-rapidity ($|η| \le$ 0.35) via $J/ψ$ $\to$ $e^{+}e^{-}$ decay and at forward rapidity (1.2 $\le | η| \le$ 2.2) via $J/ψ$ $\to$ $μ^{+}μ^{-}$ decay. The nuclear modification factor ($R_{AA}$) of $J/ψ$ is presented as a function of the collision centrality for Au+Au collisions (final results) and Cu+Cu collisions (preliminary results) in both rapidity windows. These results are compared to SPS…
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…
Measurements of identified particle momentum spectra at center of mass energy 200 GeV are reviewed. Emphasis is placed on the azimuthal dependence and the centrality dependence of hadron yields at intermediate transverse momentum (1.5 < p_T < 5 GeV/c). The first measurements of the fourth harmonic term (v_4) in the azimuthal variation of identified particle yields are shown. The recombination mechanism of hadron formation provides a consistent description of the dependence of these measurements on particle-type.
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.
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…
Large transverse single-spin asymmetries (TSSA) in hadron production at forward rapidity have been observed in polarized $p$+$p$ interactions for many decades, over a large range of center-of-mass energies, and have led to the investigation of spin-momentum correlations such as the Sivers and Collins effects. In the last few years, it has been discovered at RHIC that these single-spin asymmetries may be enhanced or suppressed in $p$+$A$ collisions, and the nuclear-size and centrality dependence have been studied. A variety of phenomena have been observed and likely they do not have all a singl…
We discuss several observables measured by PHOBOS that show common scaling features in Cu+Cu and Au+Au collisions at RHIC energies. In particular, we examine the centrality and energy dependence of the charged particle multiplicity, as well as the centrality dependence of the elliptic flow at mid-rapidity. The discrepancy between Cu+Cu and Au+Au of the final state azimuthal asymmetry (elliptic flow), relative to the initial state geometry of the collision, can be resolved by accounting for fluctuations in the description of the initial geometry.
Identified pi^[+/-] K^[+/-], p and p-bar transverse momentum spectra at mid-rapidity in sqrt(s_NN)=130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. The multiplicity densities scale faster than the number of participating nucleons. Kaon and nucleon yields per participant increase faster than the pion yields. In central collisions at high transverse momenta (p_T greater than 2 GeV/c), anti-proton and proton yields a…
Measurements of various particle species over an extended momentum range provide a sensitive experimental tool for investigating particle production mechanisms in hadronic collisions. Comparison of the spectral shapes from different collision centralities measured with the STAR detector at RHIC allows one to study the interplay of soft and hard particle production for mesons and investigate various baryon-meson effects. Systematic studies of identified particle spectra for various colliding systems and different incident energies provide additional insights toward the interplay between fragmen…
We report the first measurements of the moments -- mean ($M$), variance ($σ^{2}$), skewness ($S$) and kurtosis ($κ$) -- of the net-charge multiplicity distributions at mid-rapidity in Au+Au collisions at seven energies, ranging from $\sqrt {s_{\rm NN}}$= 7.7 to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net-charge, and are sensitive to the proximity of the QCD critical point. We compare the products of the moments, $σ^{2}/M$, $Sσ$ and $κσ^{2}$ with the expectations from Poisson and negative binomial distributions…
Recent PHENIX measurements of the elliptic (v2) and hexadecapole (v4) Fourier flow coefficients for charged hadrons as a function of transverse momentum (pT), collision centrality and particle species are presented and compared with results from the PHOBOS and STAR collaborations respectively. The status of extensions to future PHENIX measurements at lower beam energies is also discussed.
We present empirical features of parton energy loss in nucleus-nucleus collisions at RHIC through studies of the spectra and nuclear modification factors ($R_{AA}$) for charged hadrons, neutral pions ($π^0$) and non-photonic electrons. The flat distribution of $R_{AA}$ at high transverse momentum ($p_{T}$) for a given collision centrality is consistent with a scenario where parton energy loss $Δp_{T}$ is proportional to $p_{T}$. The centrality dependence of the parton energy loss indicates the absence of path length dependence in the magnitude of energy loss. The lack of strong path length dep…
It has been observed in central Au+Au collisions at Relativistic Heavy Ion Collider (RHIC) that the yield of neutral pions at high transverse momentum (pT> 5 GeV/c) is strongly suppressed compared to the one expected from p+p collisions scaled by the number of binary collisions. This suppression is considered to be due to the energy lost by hard scattered partons in the medium (jet quenching), which results in a decrease of the yield at a given pT. The magnitude of the suppression depends on the path length of scattered partons in the medium. Studying the path length dependence of energy loss …
We present the preliminary results from our analysis of event by event fluctuation in K/pi ratio in Au+Au collision at \sqrt s_{NN} = 200 GeV and at 62.4 GeV using STAR detector at RHIC. Two different methods have been used to extract the strength of dynamical fluctuation and the centrality dependence of that. The results from the study of energy and centrality dependence of the dynamical fluctuation are presented. From the excitation function it is seen that at two RHIC energies the measure of dynamical fluctuation is constant with values very close to that at 12.3 GeV at SPS. The dynamical f…
We present results for two-particle transverse momentum correlations, <dpt,i dpt,j>, as a function of event centrality for Au+Au collisions at sqrt(sNN) = 20, 62, 130, and 200 GeV at the Relativistic Heavy Ion Collider. We observe correlations decreasing with centrality that are similar at all four incident energies. The correlations multiplied by the multiplicity density increase with incident energy and the centrality dependence may show evidence of processes such as thermalization, minijet production, or the saturation of transverse flow. The square root of the correlations divided by the e…
We present STAR's measurements of directed flow for charged hadrons in Au+Au and Cu+Cu collisions at $\sqrt{s_\mathrm{NN}} = 200$ GeV and 62.4 GeV, as a function of pseudorapidity, transverse momentum and centrality. We find that directed flow depends on the incident energy, but not on the system size. We extend the validity of limiting fragmentation hypothesis to different collision systems.
We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < η< -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam…
We calculate azimuthal correlations in dAu collisions at different rapidities and centralities and argue that experimentally observed depletion of the back-to-back pick can be quantitatively explained by gluon saturation in the Color Glass Condensate of the Gold nucleus.
Strangeness enhancement has been predicted to be one of the signatures of the formation of the quark gluon plasma (QGP) and event-by-event fluctuations of strangeness may reveal the nature of such a phase transition. We report results for $K/π$ fluctuations from Cu+Cu at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV and Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4, 130 and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. We compare our results with the results observed in central Pb+Pb collisions at SPS energies at $\sqrt{s_{NN}}$ = 6.3, 7.6, 8.8, 12.3, and 17.3 GeV. We observe the f…
We present measurements of net charge and transverse momentum fluctuations in Au + Au collisions at ?sNN = 20, 130, and 200 GeV reported in our QM 2004 poster using measures ?+-,dyn and <?pt,1 ?pt,2>. We observe the dynamical fluctuations are finite at all three energies and exhibit a rather modest dependence on beam energy. We also find both net charge and pt fluctuations violate the trivial 1/N scaling expected for nuclear collisions consisting of independent nucleon-nucleon interactions. We speculate the observed centrality dependence arises due to radial flow and might provide insight on t…
In this report, we present the measurements of open charm production at mid-rapidity in p+p, d+Au, and Au+Au collisions at RHIC energies. The techniques of direct reconstruction of open charm via its hadronic decay and indirect measurements through its semileptonic decay are discussed. The beam energy dependence of total charm cross section, electron \pt spectra, and their comparisons to theoretical calculations, including NLO pQCD, are presented. The electron spectra in p+p, d+Au, and Au+Au collisions at \srt=200 GeV show significant variation. The open charm absolute cross section at midrapi…
The study of flow can provide information on the initial state dynamics and the degree of equilibration attained in heavy ion collisions. This contribution presents results for both elliptic and directed flow as determined from data recorded by the PHOBOS experiment in Au+Au runs at RHIC at sqrt(sNN) = 19.6, 130 and 200 GeV. The PHOBOS detector provides a unique coverage in pseudorapidity for measuring flow at RHIC. The systematic dependence of flow on pseudorapidity, transverse momentum, centrality and energy is discussed.
In this paper, STAR's measurement of clan multiplicity is presented for AuAu collisions at $\sqrt{s_\mathrm{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV, for a variety of centrality classes. The mean number of particles per clan is found to decrease with decreasing centrality. Within the same centrality class, the mean number of particles per clan exhibits a reduction between 19.6 GeV and 62 GeV, with the minimum around 27 GeV. The structure is visible for most centralities, and most prominent for central collisions.
Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied.
In non-central nuclear collisions, the created matter should exhibit strong vorticity, which induces spin polarization. Global polarization is a good tool to investigate the dynamics of the system. Global polarization of $Λ$ and $\barΛ$ hyperons has been measured at $\sqrt{s_{\mathrm{NN}}}$ = 2.4 GeV - 5.02 TeV in various experiments. We have measured the global polarization of $Λ$ hyperons in Au+Au collisions with fixed-target configuration at $\sqrt{s_{\mathrm{NN}}}$ = 7.2 GeV at RHIC-STAR experiment. The non-zero signal is observed and it follows the global trend of $Λ$ global polarization …
Nucleus-nucleus collisions at RHIC produce high temperature and high energy density matter which exhibits partonic degrees of freedom. We will discuss measurements of nuclear modification factors for light hadrons and non-photonic electrons from heavy quark decays, which reflect the flavor dependence of energy loss of high momentum partons traversing the dense QCD medium. The hadronization of bulk partonic matter exhibits collectivity in effective partonic degrees of freedom. Nuclear collisions at RHIC provide an intriguing environment, where many constituent quark ingredients are readily avai…
In these proceedings, we present STAR measurements of directed flow, $v_{1}$, for pions, protons and antiprotons between $\sqrt{s_{NN}} = 7.7$ GeV and 200 GeV. A striking observation is that the $v_1$ slope for net protons as a function of rapidity, $F = dv_1/dy$, which is an estimate of the directed flow contribution from baryon number transported to the midrapidity region, changes sign twice within the lower part of this energy range. We also present the measured beam energy dependence of triangular flow $v_{3}$, and the $n=1$ to $n=5$ flow harmonics for charged particles at 200 GeV.
We derive a simple analytical scaling function which embodies the predictions of high density QCD on the energy, centrality, rapidity, and atomic number dependences of hadron multiplicities in nuclear collisions. Both centrality and rapidity dependences of hadron multiplicity in $Au-Au$ collisions as measured at RHIC at $\sqrt{s}= 130 {GeV}$ are well described in this approach. The centrality and rapidity dependences of hadron multiplicity at $\sqrt{s}= 200 \ {GeV}$ run at RHIC are predicted; the variation of these dependences with energy appear different from other approaches, and can be used…
We present results on systematic measurements of strange and multi-strange particles with the STAR detector for center of mass energies per nucleon pair of 62.4 and 200 GeV in ultra-relativistic Au+Au collisions at RHIC. We use these results to characterize the chemical and kinetic freeze-out properties of the fireball produced by the collision. This is done by comparison to statistical and hydrodynamical models as well as parameterization. We emphasize particularly the energy dependence of these features comparing measurements obtained at RHIC with different energies but also at the lower ene…
