The first measurement of the $ρ^{0}$ - vector meson elliptic flow $v_{2}$ at mid-rapidity ($|y |$ $<$ 0.5) in $40 - 80$ $%$ centrality in $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR experiment at RHIC is presented. The study is through the $π^{+} π^{-}$ hadronic decay channel of $ρ^{0}$ which has a branching ratio of $\sim$ 100 %. The analysis is being carried out in two different methods. The $v_{2}$ results obtained in these methods are consistent. Number of Constituent Quark (NCQ) scaling of $v_{2}$ of $ρ^{0}$ meson with respect to other hadrons at intermediate $p_{T}$ is observed. The $ρ^{0}$ $v_{2}$ favors $NCQ = 2$ scaling, supporting the coalescence being the dominant mechanism of hadronization in the intermediate $p_{T}$ region at RHIC.
We present the measurement of elliptic flow ($v_{2}$) as a function of transverse momentum ($p_{T}$) for the $ϕ$-meson in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5 and 39 GeV. At low $p_{T}$ $ϕ$-meson $v_{2}$ decreases with decrease in beam energy. The number of constituent quark ($n_{\rm{cq}}$) scaled $v_{2}$ for $ϕ$-meson vs ($m_{T} - m_{0}$)/$n_{\rm{cq}}$ follows similar trend as other hadrons for $\sqrt{s_{NN}}$= 39 GeV whereas the $n_{\rm{cq}}$ scaled $v_{2}$ for $ϕ$-mesons follows a different trend compared to the other hadrons at $\sqrt{s_{NN}}$= 11.5 GeV.
We report the transverse momentum ($p_{\mathrm{T}}$) and centrality dependence of global spin alignment ($ρ_{00}$) of $K^{*0}$ vector meson at midrapidity ($|y|<0.5$) in Au + Au collisions at $\sqrt{s_{NN}}$ = 54.4 and 200~GeV with the STAR experiment at RHIC. The $K^{*0}$ results are compared to that of $ϕ$ meson. At low-$p_{\mathrm{T}}$ region and midcentral collisions, the $K^{*0}$ $ρ_{00}$ is found to be smaller than 1/3 with about 4$σ$ significance, while that of $ϕ$ meson is observed to be larger than 1/3 with about 3$σ$ significance. The $ρ_{00}$ results are compared between RHIC and LH…
We present the first measurement for the $B$ meson semi-leptonic decay contribution to non-photonic electrons at RHIC using non-photonic electron azimuthal correlations with charged hadrons in p+p collisions at $\sqrt{s_{NN}} = 200$ GeV from STAR.
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.
In this letter we update our predictions for the photoproduction of vector mesons in coherent $pp$ and $AA$ collisions at RHIC and LHC energies using the color dipole approach and the Color Glass Condensate (CGC) formalism. In particular, we present our predictions for the first run of the LHC at half energy and for the rapidity dependence of the ratio between the $J/Ψ$ and $ρ$ cross sections at RHIC energies.
The PHENIX experiment at RHIC measured K0S, eta and omega-meson production at high pT in p+p, d+Au and Au+Au collisions at sqrt(s_NN)=200 GeV. Measurements performed in different hadronic decay channels give consistent results. This paper presents measured meson-to-pi0 ratios and Nuclear Modification factors in the most central d+Au and Au+Au collisions. No suppression seen in d+Au interactions is in contrast to a strong suppression of meson yields revealed in central Au+Au collisions at the same energy.
The PHENIX experiment at RHIC has measured a variety of light neutral mesons ($π^{0}$, K$_{S}^{0}$, $η$, $ω$, $η^{\prime}$, $ϕ$) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p+p and their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at different energies is presented.
We report the measurements of spin alignment ($ρ_{00}$) for $K^{*0}$, $\overline{K^{*0}}$, $K^{*+}$, and $K^{*-}$ vector mesons in RHIC isobar collisions (Zr+Zr and Ru+Ru) at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. We observe the first non-zero spin alignment for $K^{*\pm}$ in heavy-ion collisions. The $K^{*\pm}$ $ρ_{00}$ is about 3.9$σ$ larger than that of $K^{*0}$. The observed difference and the ordering between $K^{*\pm}$ and $K^{*0}$ are surprising, and require further inputs from theory. When comparing between the isobar and Au+Au collisions, no significant system size dependence in $K^{*0}…
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.
The PHENIX experiment at RHIC measured production of the ω- and ϕ- mesons in p+p, d+Au and Au+Au collisions at \sqrt{s_NN} = 63 and 200 GeV. Particle properties were studied using hadronic and di-electron decay channels. Transverse momentum (mass) spectra measured in different decay modes are found to be in agreement with each other within the errors. Nuclear modification factors R_{AA} measured for both mesons are consistent with results previously obtained for other neutral mesons. Position of the meson mass peaks and their widths reconstructed in hadronic decay channels are in agreement wit…
We report the preliminary results of the azimuthal correlations between $D^{*\pm}$ mesons and charged hadrons ($D^{*}$-h) measured by the STAR experiment in proton+proton collisions at $\sqrt{s}$ = 500 GeV. Results at mid-rapidity in the transverse-momentum range 8 $\le$ $p^{D^{*}}_{T}$ $\le$ 20 GeV/$c$ are compared with light hadron triggered correlations (h-h) and PYTHIA predictions. We also present an exploratory study of azimuthal correlations between $D^{*+}$ and $D^{*-}$ mesons in p+p collisions. The prospects of measuring heavy-flavor triggered correlations in heavy-ion collisions at RH…
The PHENIX experiment at RHIC has measured the ϕ-meson production at mid-rapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at \sqrt{s_{NN}}=200 GeV via the K^+K^- decay mode. The transverse momentum spectra of the ϕ-meson and the nuclear modification factor as a function of centrality are reviewed here.
We report the elliptic flow ($v_{2}$) of $K_{s}^{0}$, $Λ$, $\barΛ$, $ϕ$, $Ξ^{-}$, and $\overlineΞ^{+}$ at mid-rapidity for Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The transverse momentum ($p_{T}$) and centrality dependence of $v_{2}$ have been studied. The number of constituent quark (NCQ) scaling for all the (multi-)strange hadrons has also been tested. The dependence in the ratio of average $v_{2}$ ($\langle$$v_{2}$$\rangle$) on centrality shows a deviation from unity indicating a difference in nuclear structure and deformation between the isobars. The results show…
Measurements at RHIC have established the creation of a Quark Gluon Plasma (QGP) in most central heavy-ion collisions. An important tool to understand properties of the QGP is study of the spectral shapes of low-mass vector mesons (LVM's), $ρ$, $ω$ and $ϕ$, which can be modified in the medium by partial restoration of chiral symmetry. This modification may be accessed directly by measuring low-momentum LVM's via their decays into lepton pairs inside the hot matter. Since leptons are not subject to the strong interaction, they do not rescatter on their way out of the medium. The PHENIX experime…
Recent PHENIX elliptic flow ($v_2$) measurements for identified particles produced in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV are presented and compared to other RHIC measurements. They indicate universal scaling of $v_2$ compatible with partonic collectivity leading to the flow of light, strange and heavy quarks with a common expansion velocity field.
The PHENIX experiment at RHIC measured $ω$, $η$ and $K_{S}^{0}$-meson production at high $p_{T}$ in $p+p$, $d+Au$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ $GeV$. Measurements performed in different hadronic decay channels give consistent results. The measured ratios of all three mesons to $π^{0}$ are found to be flat as a function of $p_{T}$ in $p+p$ collisions and equal to $ω/π^{0}=0.81\pm0.02\pm0.07$, $η/π^{0}=0.48\pm0.02\pm0.02$ and $K_{S}^{0}/π^{0}=0.45\pm0.01\pm0.05$. Nuclear modification factor measured for $ω$-mesons in central Au+Au collisions is $R_{AA}=0.4\pm0.15$.
The pi0 meson has been a crucial proble for observing jet quenching in ultrarelativistic heavy-ion collisions at RHIC. Measurements of the eta meson in the same collisions have also shed light on a possible dependence of the observed suppression on the particle species. The preliminary pi0 nuclear modification factor R_AA from the 2004 RHIC run allowed a first systematic comparison between a precise measurement with high statistics and theoretical calculations, constraining model parameters such as the initial gluon density dN^g/dy, and the transport coefficient qhat. The final pi0 spectra and…
Elliptic flow is an interesting probe of the dynamical evolution of the dense system formed in the ultrarelativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector, which offers a unique opportunity to study the azimuthal anisotropies of charged particles over a wide range of pseudorapidity. These measurements are presented, together with an overview of the analysis methods and a discussion of the results.
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 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.
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…
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.
New results on $ϕ$-meson production and elliptic flow $v_{2}$ measurements from RHIC 2004 run (Run-IV) have been reviewed. In addition, the di-hadron correlation function between the trigged $ϕ$ and $Ω$ and the associated soft particles was simulated. Knowledge about these results are discussed.
Heavy quarks are produced through initial hard scatterings and they are affected by the hot and dense medium created in heavy-ion collisions throughout its whole evolution. Due to their heavy mass, charm quarks are expected to thermalize much more slowly than light flavor quarks. The charm quark flow is a unique tool to study the extent of thermalization of the bulk medium dominated by light quarks and gluons. At high $p_T$, D meson azimuthal anisotropy is sensitive to the path length dependence of charm quark energy loss in the medium, which offers new insights into heavy quark energy loss me…
We present first results on event-by-event elliptic flow fluctuations in Au+Au collisions at 200 GeV obtained with the PHOBOS detector. Over the measured range in centrality, large relative fluctuations of 40--50% are found. The elliptic flow fluctuations are well described as being proportional to fluctuations in the shape of the initial collision region, as estimated event-by-event with the participant eccentricity using Glauber Monte Carlo.
Detailed measurements of the azimuthal anisotropy (\v2) for identified charged particles are reported as a function of transverse momentum ($p_T$) and centrality for Au+Au collisions at \sqrtsNN = 200 GeV. The measurements indicate clear evidence for eccentricity and particle flavor scaling over a broad range of centralities and transverse rapidity $y_T$, indicating a hydrodynamical origin of the fine structure of azimuthal anisotropy at RHIC. The observed scaling supports the picture of a suddenly hadronizing (recombining) fluid of quarks. An apparent breaking of flavor scaling at relatively …
Flow measurements are reviewed with particular emphasis on the hydrodynamic character of elliptic flow at RHIC. Hydrodynamic scaling compatible with the production of highly thermalized matter having a high degree of collective interactions and extremely low viscosity, is observed for a broad selection of the data. These properties suggest the production of a new state of strongly interacting nuclear matter at extremely high density and temperature where the relevant degrees of freedom are those of quarks and gluons, ie. the sQGP.
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 results for the measurement of $ϕ$ meson production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion Collider (RHIC). Using the event mixing technique, spectra and yields are obtained from the $ϕ\to K^{+}K^{-}$ decay channel for different centrality bins in Au+Au collisions and in pp collisions. We observe that the spectrum shape in Au+Au collisions depends weakly on the centrality and the shape of the spectrum in pp collisions is significantly different from that in Au+Au collisions. In Au+Au collisions, the extracted yield of $ϕ$ meson is flat…
With RHIC running in its second phase at higher luminosities the new data sets collected so far by PHENIX and STAR are allowing improvements in the study of vector meson photo-production in Ultra peripheral Collision events in Au+Au at the highest energy. This is a brief summary of what has been accomplished so far by both collaborations.
We present predictions for the J/psi and rho meson production in the heavy ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the LHC. Both total cross sections and cross sections with the neutron emission from one or both nuclei are presented. We also analyse the RHIC rho meson photoproduction data and emphasize importance of these data to test the current model for nucleus break up in UPC.
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 observation of meson and baryon grouping in the $R_{CP}$ and $v_2$ measurements at intermediate $p_T$ has been interpreted as a manifestation of bulk partonic matter hadronization through multi-parton dynamics such as recombination of partons. $ϕ$ mesons provide unique sensitivity to test these theoretical scenarios, since the $ϕ$ has a mass heavier than the proton and close to the hyperons. The $R_{CP}$ and $v_2$ measurements of $ϕ$ mesons from Run IV Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at STAR are presented. Energy and colliding system dependence of the $ϕ$ yields at mid-rapidity…
We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the in…
The measurement of phi mesons provides a unique and complementary method for exploring properties of the hot and dense medium created in the relativistic heavy ion collisions. It has a relatively small hadronic interaction cross section and is sensitive to the increase of strangeness (strangeness enhancement), a phenomenon associated with soft particles in bulk matter. Measurements in the dilepton channels are especially interesting since leptons interact only electromagnetically, thus carrying the information from their production phase directly to the detector. Measurements in different nucl…
We report on the first evidence for a non-zero rapidity-odd directed flow ($v_{1}$) for $D^{0}$ and $\overline{D^{0}}$ mesons in 10-80\% centrality Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200~GeV measured with the STAR detector at RHIC. The slope of the $v_1$ rapidity dependence ($dv_{1}/dy$) averaged over $D^{0}$ and $\overline{D^{0}}$ mesons is -0.081 $\pm$ 0.021 $\pm$ 0.017, while that of charged kaons is -0.0030 $\pm$ 0.0001 $\pm$ 0.0002, suggesting significantly larger slope for the $D^{0}$ mesons. Models indicate that the large $dv_{1}/dy$ of $D^{0}$ mesons is sensitive to the initiall…
We present a systematic study of elliptic flow as a function of centrality, pseudorapidity, transverse momentum and energy for Cu+Cu and Au+Au collisions from the PHOBOS experiment. New data on elliptic flow in Cu+Cu collisions at 22.4 GeV are shown. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same average area density are compared. This similarity is observed over a wide range in pseudorapidity and transverse momentum, indicating that participant eccentricity is the relevant quantity for g…
We argue that with an increase of the collision energy, elastic photoproduction of $ρ$ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction into large masses, which results in the sizable inelastic nuclear shadowing correction to $σ_{γA \to ρA}$ and the reduced effective $ρ$-nucleon cross section. We take these effects into account by combining the vector meson dominance model, which we upgrade to include the contribution of high-mass fluctuations of the photon according to QCD constraints, and the Gribov-Glauber approximation for nuclear shadowing…
We present results for the measurement of $ϕ$ meson production via its charged kaon decay channel $ϕ\to K^+K^-$ in Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$, 130, and 200 GeV, and in $p+p$ and $d$+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV from the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC). The midrapidity ($|y|<0.5$) $ϕ$ meson transverse momentum ($p_{T}$) spectra in central Au+Au collisions are found to be well described by a single exponential distribution. On the other hand, the $p_{T}$ spectra from $p+p$, $d$+Au and peripheral Au+Au collisions show power-law tai…
We calculate the elliptic flow of thermal photons from Au+Au collisions at RHIC energies for a range of values for the formation time $τ_0$ but fixed entropy (or particle rapidity density). The results are found to be quite sensitive to $τ_0$. The $v_2$ for photons decreases as $τ_0$ decreases and admits a larger contribution from the QGP phase which has a smaller $v_2$. The elliptic flow coefficient for hadrons, on the other hand, is only marginally dependent on $τ_0$.
The strong electromagnetic fields of heavy nuclei can produce a wide variety of two-photon and photonuclear reactions at relativistic ion colliders. We present recent results from the STAR collaboration on these `ultra-peripheral' interactions, focusing on vector meson production and interferometry, and on $e^+e^-$ pair production. The vector meson interferometry occurs because of the symmetric initial state: nucleus 1 can emit a photon which scatters from nucleus 2, emerging as a vector meson, or vice-versa. The two processes are indistinguishable, and so interfere, even though the production…
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 …
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. …
We obtain the radiative energy loss of a heavy quark in a deconfined medium due to radiation of gluons off them using a recently derived generalised gluon emission spectrum. We find that the heavy flavour loses energy almost in a similar fashion like light quarks through this process. With this, we further analyse the nuclear modification factor for D-meson at LHC and RHIC energies. In particular, the obtained result is found to be in close agreement with the most recent data from ALICE collaboration at 2.76 ATeV Pb-Pb collisions. We also discuss the nuclear modification factor due to the coll…
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…
The elliptic flow splitting between particles and their antiparticles has recently been observed by the STAR Collaboration in the beam-energy scan program at the Relativistic Heavy Ion Collider. In studies based on transport models, we have found that this splitting can be explained by the different mean-field potentials acting on particles and their antiparticles in the produced baryon-rich matter. In particular, we have shown that the experimentally measured relative elliptic flow difference can help constrain the vector coupling constant in the Nambu-Jona-Lasinio model used in describing th…
Measurements from the RHIC experiments show strong suppression of high-pT hadrons in central Au+Au collisions. The PHENIX experiment has observed strong suppression of $π^0$ and charged hadron yields in central Au+Au collisions for pT > 5 GeV/c regardless of pT and particle species. The observed suppression is interpreted in terms of energy loss of quarks in a high-density medium. The PHENIX Year-4 Au+Au measurements have extended the pT reach of the $π^0$ spectra to 20 GeV/c. And the PHENIX Year-5 Cu+Cu measurements performed for the study of particle production in a lighter system and they c…
A study of elliptic flow of open charm mesons, $D^0$ and $D_S ^\pm$ using quark coalescence as a mechanism of hadronization of heavy quarks implemented in conjunction with A Multi Phase Transport (AMPT) model has been presented. We have studied the transverse momentum dependence of the elliptic flow parameter at mid-rapidity ($|y|$ $<$ 1.0) for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV (LHC) for different values of partonic interaction cross-section and QCD coupling constant. We have compared our calculations with the experimentally…
Within a covariant parton cascade, we discuss the impact of both finite shear viscosity $η$ and freeze-out dynamics on the elliptic flow generated at RHIC. We find that the enhancement of $η/s$ in the cross-over region of the QGP phase transition cannot be neglected in order to extract the information from the QGP phase. We also point out that the elliptic flow $v_2(p_T)$ for a fluid at $η/s \sim 0.1-0.2$ is consistent with the one needed by quark number scaling drawing a nice consistency between the nearly perfect fluid property of QGP and the coalescence process.
The elliptic flow ($v_{2}$) at $\sqrt{s_{\rm NN}} = $ 11.5, 39, and 200 GeV and triangular flow ($v_{3}$) at $\sqrt{s_{\rm NN}} = $ 200 GeV of identified particles ($π^{\pm}, K^{\pm}, K^{0}_{S}, p, \bar{p}, ϕ, Λ$ and $\barΛ$) from 0\%--80\% central Au+Au collisions are analyzed using a multiphase transport (AMPT) model. It is shown that the experimental results from the $η$-sub event plane method can be reproduced with a parton scattering cross section between 1.5 and 3 mb. We also studied the differential and integrated $v_{2}/v_{3}$ ratios and conclude that they are anti-corrected with the p…
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…
In this work, we calculate energy loss of heavy quark (charm and bottom) due to elastic collisions and gluon radiation in hot/dense medium. The collisional energy loss has been obtained using QCD calculations. The radiative energy loss is calculated using reaction operator formalism and generalized dead cone approach. We rederive the energy loss expression using same assumptions as generalized dead cone approach but obtain slightly different results. We also improve the model employed to calculate path length and the system evolution. The nuclear modification factors $R_{AA}$ including shadowi…
Anisotropic flow of kaons and antikaons is studied in heavy-ion collisions at CERN SPS and BNL RHIC energies within the microscopic quark-gluon string model. In the midrapidity range the directed flow of kaons v_1 differs considerably from that of antikaons at SPS energy (E_{lab} = 160 AGeV), while at RHIC energy (\sqrt{s} = 130 AGeV) the excitation functions of both, kaon and antikaon, flows coincide within the statistical error bars. The change is attributed to formation of dense meson-dominated matter at RHIC, where the differences in interaction cross-sections of kaons and antikaons become…
We present a review of the measurements of elliptic flow ($v_{2}$) of light nuclei ($d$,$\bar{d}$, $t$, $^{3}\rm He$, and $^{3}\overline{\rm He}$) from the RHIC and LHC experiments. Light (anti)nuclei $v_{2}$ have been compared with that of (anti)proton. We observed a similar trend in light nuclei $v_{2}$ to that in identified hadron $v_{2}$ with respect to the general observations such as ($p_{\rm T}$) dependence, low $p_{\rm T}$ mass ordering, and centrality dependence. We also compared the difference of nuclei and antinuclei $v_{2}$ with the corresponding difference of $v_{2}$ of proton and…
We present the first spin alignment measurements for the $K^{*0}(892)$ and $ϕ(1020)$ vector mesons produced at mid-rapidity with transverse momenta up to 5 GeV/c at $\sqrt{s_{NN}}$ = 200 GeV at RHIC. The diagonal spin density matrix elements with respect to the reaction plane in Au+Au collisions are $ρ_{00}$ = 0.32 $\pm$ 0.04 (stat) $\pm$ 0.09 (syst) for the $K^{*0}$ ($0.8<p_T<5.0$ GeV/c) and $ρ_{00}$ = 0.34 $\pm$ 0.02 (stat) $\pm$ 0.03 (syst) for the $ϕ$ ($0.4<p_T<5.0$ GeV/c), and are constant with transverse momentum and collision centrality. The data are consistent with the unpolarized expe…
We use an event-by-event hydrodynamical description of the heavy-ion collision process with Glauber initial conditions to calculate the thermal emission of photons. The photon rates in the hadronic phase follow from a spectral function approach and a density expansion, while in the partonic phase they follow from the AMY perturbative rates. The calculated photon elliptic flows are lower than those reported recently by both the ALICE and PHENIX collaborations.
Directed and elliptic event anisotropy parameters measured in the experiments at relativistic heavy-ion collider are presented. The possible origin of the measured elliptic anisotropy parameter $v_2$ and its sensitivity to the early phase of the high-energy heavy-ion collisions are discussed.
We present the first results of meson production in the K^+K^- decay channel from Au+Au collisions at sqrt(s_NN) = 200 GeV as measured at mid-rapidity by the PHENIX detector at RHIC. Precision resonance centroid and width values are extracted as a function of collision centrality. No significant variation from the PDG accepted values is observed. The transverse mass spectra are fitted with a linear exponential function for which the derived inverse slope parameter is seen to be constant as a function of centrality. These data are also fitted by a hydrodynamic model with the result that the fre…
Elliptic flow measurements are presented and discussed with emphasis on the hydrodynamic character of the hot and dense QCD matter created in heavy ion collisions at RHIC. Predictions from perfect fluid hydrodynamics for the scaling of the elliptic flow coefficient $v_2$ with eccentricity, system size and transverse energy are validated. A universal scaling for the flow of both mesons and baryons is observed for a broad transverse kinetic energy range when quark number scaling is employed. This suggests a new state of nuclear matter at extremely high density and temperature whose primary const…
