The Study of Noncollectivity by the Forward-Backward Multiplicity Correlation Function

We propose a forward-backward multiplicity correlation function $C^N_{FB}$, which is experimentally accessible, to measure the noncollectivity contribution. We find that $C^N_{FB}$ is sensitive to the jet contribution for the particle-rich case. Surprisingly, it will automatically decrease for the particle-rare case. Our study indicates that similar decreasing trend observed previously is mainly driven by particle scarcity instead of jets. The function is studied in Au+Au collision at $\sqrt{s_{NN}}=200$ GeV with a multiphase transport model (AMPT). We find that the jet fraction is about 10% at transverse momentum ($p_T$) around 2.5 GeV/$c$ and reaches up to 30% at 3.5 GeV/$c$. The implication of this study in the investigation of the noncollectivity contribution in elliptic anisotropy parameter $v_2$ is also discussed.Comment: 5 pages, 4 figure

Measurements of high pTp_{T} identified particles v2v_{2} and v4v_{4} in sNN=200\sqrt{s_{NN}} = 200 GeV Au+Au collisions by PHENIX

The $v_{2}$ and $v_{4}$ of pions, kaons and protons have been measured by PHENIX in 200 GeV Au+Au collisions up to $p_{T}$$\sim$6 GeV/c and 4 GeV/c, respectively. The $v_{4}$ of all these identified particles have been found to scale with the number of constituent quarks and all these particles have a similar $v_{4}$/$v_{2}^{2}$ ratio which is close to 0.9. The scaling behavior of $v_2$ is studied at high-$p_{T}$ and a deviations from the universal scaling is observed for transverse kinetic energy ($K_{ET}/nq$) higher than 1 GeV.Comment: 4 pages, 3 figures, proceedings of 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 04-10 Feb 200

Parton Collectivity from RHIC to the LHC

Anisotropic flow is recognized as one of the main observables providing information on the early dynamics in heavy-ion collisions. The large elliptic flow observed at RHIC is considered to be evidence for almost perfect liquid behavior of the strongly coupled Quark Gluon Plasma produced in the collisions. In this report we review our current understanding of this new state of matter and investigate the predictions for anisotropic flow at the LHC.Comment: 8 pages, proceedings SQM 200

Directed and Elliptic Flow at RHIC

We present the directed flow measurement ($v_1$) from Au+Au collisions at \sqrtsNN = 62 GeV. Over the pseudorapidity range we have studied, which covers $\eta$ from -1.2 to 1.2 and $2.4 < |\eta| < 4$, the magnitude of $v_1$ for charged particles is found to increase monotonously with pseudorapidity for all centralities. No ``$v_1$ wiggle'', as predicted by various theoretical models, is observed at midrapidity. Elliptic flow ($v_2$) from moderate high $p_t$ particles ($3-6 GeV/c$) at \sqrtsNN = 200 GeV is presented as a function of impact parameter. It is found that models that are based on {\it jet quenching} alone appear to underpredict $v_2$ at moderate high $p_t$, while the model that incorporates both, recombination and fragmentation, describes the data better.Comment: 6 pages, 4 figures. Proceeding for Hot Quark 04 conference Changes in the revision are mostly English fixes. v1 versus eta plot is flipped over to follow the conventio

Transverse momentum dependence of directed particle flow at 160 AGeV

The transverse momentum ($p_t$) dependence of hadron flow at SPS energies is studied. In particular, the nucleon and pion flow in S+S and Pb+Pb collisions at 160 AGeV is investigated. For simulations the microscopic quark-gluon string model (QGSM) is applied. It is found that the directed flow of pions $v_1(y, \Delta p_t)$ changes sign from a negative slope in the low-$p_t$ region to a positive slope at $p_t \geq 0.6$ GeV/c as recently also observed experimentally. The change of the flow behaviour can be explained by early emission times for high-$p_t$ pions. We further found that a substantial amount of high-$p_t$ pions are produced in the very first primary NN collisions at the surface region of the touching nuclei. Thus, at SPS energies high-$p_t$ nucleons seem to be a better probe for the hot and dense early phase of nuclear collisions than high-$p_t$ pions. Both, in the light and in the heavy system the pion directed flow $v_1(p_t, \Delta y)$ exhibits large negative values when the transverse momentum approaches zero, as also seen experimentally in Pb+Pb collisions. It is found that this effect is caused by nuclear shadowing. The proton flow, in contrary, shows the typical linear increase with rising $p_t$.Comment: REVTEX, 20 pages incl. 6 figures, revised and extended versio

Higher Flow Harmonics in Heavy Ion Collisions from STAR

We report STAR measurements relating to higher flow harmonics including the centrality dependence of two- and four-particle cumulants for harmonics 1 to 6. Two-particle correlation functions vs. \Delta\eta and \Delta\phi are presented for pT and number correlations. We find the power spectra (Fourier Transforms of the correlation functions) for central collisions drop quickly for higher harmonics. The \Delta\eta dependence of v3{2}2 and the pT and centrality dependence of v2 and v3 are studied. Trends are conistent with expectations from models including hot-spots in the initial energy density and an expansion phase. We also present v3 and v2{2}2 - v2{4}2 vs. \surdsNN .Comment: 8 pages. Conference proceedings for Quark Matter 201

Flow analysis from multiparticle azimuthal correlations

We present a new method for analyzing directed and elliptic flow in heavy ion collisions. Unlike standard methods, it separates the contribution of flow to azimuthal correlations from contributions due to other effects. The separation relies on a cumulant expansion of multiparticle azimuthal correlations, and includes corrections for detector inefficiencies. This new method allows the measurement of the flow of identified particles in narrow phase-space regions, and can be used in every regime, from intermediate to ultrarelativistic energies.Comment: 31 pages, revtex. Published version (references added

Flow at the SPS and RHIC as a Quark Gluon Plasma Signature

Radial and elliptic flow in non-central heavy ion collisions can constrain the effective Equation of State(EoS) of the excited nuclear matter. To this end, a model combining relativistic hydrodynamics and a hadronic transport code(RQMD [17]) is developed. For an EoS with a first order phase transition, the model reproduces both the radial and elliptic flow data at the SPS. With the EoS fixed from SPS data, we quantify predictions at RHIC where the Quark Gluon Plasma(QGP) pressure is expected to drive additional radial and elliptic flow. Currently, the strong elliptic flow observed in the first RHIC measurements does not conclusively signal this nascent QGP pressure. Additional measurements are suggested to pin down the EoS.Comment: 4 pages, 4 figures. Revised. Included discussed of v_2 (p_t) vs. b and comparison to STAR dat

Parton coalescence at RHIC

Using a covariant coalescence model, we study hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons in minijets. Including transverse flow of soft partons and independent fragmentation of minijet partons, the model is able to describe available experimental data on pion, kaon, and antiproton spectra. The resulting antiproton to pion ratio is seen to increase at low transverse momenta and reaches a value of about one at intermediate transverse momenta, as observed in experimental data at RHIC. A similar dependence of the antikaon to pion ratio on transverse momentum is obtained, but it reaches a smaller value at intermediate transverse momenta. At high transverse momenta, the model predicts that both the antiproton to pion and the antikaon to pion ratio decrease and approach those given by the perturbative QCD. Both collective flow effect and coalescence of minijet partons with partons in the quark-gluon plasma affect significantly the spectra of hadrons with intermediate transverse momenta. Elliptic flows of protons, Lambdas, and Omegas have also been evaluated from partons with elliptic flows extracted from fitting measured pion and kaon elliptic flows, and they are found to be consistent with available experimental data.Comment: 12 pages, 11 figure