Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session CC: Mini-Symposium on Thermal and Collective Properties of the Quark Gluon Plasma I |
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Chair: ShinIchi Esumi, University of Tsukuba Room: Kohala 1 |
Thursday, October 15, 2009 9:00AM - 9:30AM |
CC.00001: What We Have Learned from the Measurement of Azimuthal Anisotropy of Identified Particles in Relativistic Heavy ion Collisions Invited Speaker: Measuring the azimuthal anisotropy of particles produced in relativistic heavy ion collisions is a powerful probe for investigating the characteristics of the quark-gluon plasma (QGP), which is the phase in QCD matter of de-confined quarks and gluons. The strength of the elliptic anisotropy (v$_{2})$ in the momentum phase space is transferred from the geometrical anisotropy of the initial collisional region because of the pressure gradient. Thus, the measured v$_{2}$ reflects the equation of state of the dense matter, possibly the QGP, produced in the collisions. One of the most remarkable findings at RHIC is that the v$_{2}$ can be well described by hydro dynamical models assuming very short thermalization times ($<$ 0.5 fm/c) in the low transverse momentum region (p$_{T} \quad \le \quad \sim $ 1 GeV/c). In the intermediate transverse momentum region (p$_{T}$ =1$\sim $4 GeV/c), v$_{2}$ is scaled with the number of quarks, and consistent with the quark-recombination model. For a more comprehensive understanding of v$_{2}$, we have carried out systematic measurements of v$_{2}$ and studied the dependence on collision energy, species and centrality. We find that v$_{2}$ divided by the participant eccentricity of initial geometry exponentially increases with the number of participants to the 1/3 power. Taking the eccentricity and quark number scaling into account, there is a universal scaling for v$_{2}$ with different energies and collision sizes. The results indicate that v$_{2}$ is not decided by only the geometrical eccentricity, but it also depends on the size of collision, which can be related to the finite evolving time up to freeze out. [Preview Abstract] |
Thursday, October 15, 2009 9:30AM - 9:45AM |
CC.00002: Directed and Elliptic flow measured by STAR Experiment for AuAu collisions at \mbox{$\sqrt{s_{_{NN}}}$}=200 GeV Aihong Tang With large statistics obtained in RHIC run VII, directed flow measurements for charged particles are extended to $p_t$ as large as 8 GeV/c, for AuAu collisions at \mbox{$\sqrt{s_{_{NN}}}$}=200 GeV. The directed flow of pion, proton, kshort and lambda will be reported. The wiggle structure as a signature of the first order phase transition is not observed within the statistical significance of the present measurements. Comparison to previous measurements will be made. Elliptic flow scaled by initial eccentricity ($v_2/\varepsilon$) as a function of particle density in the transverse plane ($1/{\rm S} \, {\rm d}N/{\rm dy}$) is fitted with transport model motivated formula. Measurements of event anisotropy at \mbox{$\sqrt{s_{_{NN}}}$}= 200 GeV are compared to transport calculations. It is found that the $1/{\rm S} \, {\rm d}N/{\rm dy}$ dependence of $v_2/\varepsilon$ can be described well by transport models with finite Knudsen numbers. The result indicates that the system has not yet reached ideal hydrodynamic limits even for central collisions. Constrains on the product of the cross section and the speed of sound are provided, eta/s is estimated. The Knudsen fit is also applied to $v_2$ from viscous hydro calculations and the result is compared to data. [Preview Abstract] |
Thursday, October 15, 2009 9:45AM - 10:00AM |
CC.00003: Azimuthal Anisotropy of Unidentified Hadrons at Forward Rapidity in PHENIX at RHIC Eric Richardson At the Relativistic Heavy Ion Collider (RHIC), where Au nuclei are collided at 200 GeV per nucleon pair, key insights into the bulk properties of the newly formed matter have been made by studying the azimuthal anisotropy ($v_{2}$) of the produced particles. Studies of $v_{2}$ have shown that the hot dense matter undergoes rapid thermalization and behaves hydrodynamicaly at low $p_{T}$. Furthermore, the quark scaling of the $v_{2}$ signal for different particle species suggests that thermalization occurs at the quark level and that $v_{2}$ is the same for all quark flavors. This analysis will attempt to expand upon these principles by examining the $v_{2}$ of unidentified hadrons in the less studied pseudorapidity region of $|1.2|<\eta<|2.0|$ using PHENIX's forward arm detectors. The analysis procedure and results will be explored. [Preview Abstract] |
Thursday, October 15, 2009 10:00AM - 10:15AM |
CC.00004: Partonic collectivity at RHIC Shusu Shi The measurement of event anisotropy, often called $v_{2}$, provides a powerful tool for studying the properties of hot and dense medium created in high-energy nuclear collisions. The important discoveries of partonic collectivity and the brand-new process for hadronization - quark coalescence were obtained through a systematic analysis of the $v_{2}$ for 200 GeV Au+Au collisions at RHIC [1]. However, early dynamic information might be masked by later hadronic rescatterings. Multistrange hadrons ($\phi$, $\Xi$ and $\Omega$) with their large mass and presumably small hadronic cross sections should be less sensitive to hadronic rescattering in the later stage of the collisions and therefore a good probe of the early stage of the collision. We will present the measurement of $v_{2}$ of $\pi$, p, $K_{S}^{0}$, $\Lambda$, $\Xi$, $\phi$ and $\Omega$ in heavy ion collisions. In minimum-bias Au+Au collisions at $\sqrt{\mathrm{s}_{_{\mathrm{NN}}}}$ = 200 GeV, a significant amount of elliptic flow, almost identical to other mesons and baryons, is observed for $\phi$ and $\Omega$. Experimental observations of $p_{T}$ dependence of $v_{2}$ of identified particles at RHIC support partonic collectivity. \\[4pt] [1] B. I. Abelev et al., (STAR Collaboration), Phys. Rev. {\bf C 77}, 054901 (2008). [Preview Abstract] |
Thursday, October 15, 2009 10:15AM - 10:30AM |
CC.00005: Bridging the soft and the hard at RHIC Jiangyong Jia Measurements from RHIC at intermediate $p_T$ of 2-6 GeV/c revealed many features in various single particle and two particle correlation observables. These measurements not only suggest the leading roles of collective flow and jets in this $p_T$ region, but also show how strong and sophisticated the coupling between the two is. Experimental results are discussed in the hope to elucidate the connections between the soft and the hard processes. [Preview Abstract] |
Thursday, October 15, 2009 10:30AM - 10:45AM |
CC.00006: Predictions in $^{238}$U + $^{238}$U collisions at RHIC Hiroshi Masui Planed $^{238}$U + $^{238}$U collisions at RHIC (2012) would provide opportunities to answer several open questions at RHIC. For example, the ratio of elliptic flow $v_2$ to the initial spatial anisotropy $\varepsilon$ as a function of transverse number density would indicate to the extent which the system approaches the ideal hydrodynamical limit. The saturation of $v_2/\varepsilon$ could indicate that the system reaches local thermal equilibrium. Until now, there were no hint of saturation even at most central $^{197}$Au + $^{197}$Au collisions at top RHIC energy. Due to the larger size and the deformation of Uranium, the $^{238}$U + $^{238}$U collisions could reach higher densities than that achieved in $^{197}$Au + $^{197}$Au collisions at the same energy. In this talk, we present the predictions of various observables in $^{238}$U + $^{238}$U collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV at RHIC. We discuss our Glauber Monte Carlo model to extrapolate the observables from $^{197}$Au + $^{197}$Au to $^{238}$U + $^{238}$U collisions at top RHIC energy and show the results as a function of centrality. [Preview Abstract] |
Thursday, October 15, 2009 10:45AM - 11:00AM |
CC.00007: Bulk Viscous Effects on Relativistic Hydrodynamic Models of the Quark-Gluon Plasma Akihiko Monnai, Tetsufumi Hirano The quark-gluon plasma (QGP) created at Relativistic Heavy Ion Collider (RHIC) is well described within the framework of ideal hydrodynamic models. Our next step is to develop the treatment for viscosity in relativistic hydrodynamics. We mainly discuss the effects of bulk viscosity because recent studies suggest that it becomes large near the pseudo-phase transition temperature. Viscous corrections are brought into QGP physics through (i) modification of the distribution $\delta f$ and (ii) variation of the flow $\delta u^\mu$ and the hypersurface $\delta d\sigma _\mu$. In this work we determine the former uniquely in Grad's 14-moment method for a multi-component system. Effects of both shear and bulk viscosity on the QGP phenomena is discussed, along with the prospect for the consistent development of viscous hydrodynamic models to estimate $\delta u^\mu$ and $\delta d\sigma _\mu$. We see that bulk viscous effects can be large, and that they should be treated with care in constraining the transport coefficients and/or the equation of state with precision from experimental data. [Preview Abstract] |
Thursday, October 15, 2009 11:00AM - 11:15AM |
CC.00008: Systematic Approach to Knudsen Number and Viscosity Extraction Jamie Nagle, Peter Steinberg, Bill Zajc We explore the determination of the Knudsen Number ($K$) and shear viscosity to entropy density ratio ($\eta/s$) from experimental data at the Relativistic Heavy Ion Collider. We detail the various inputs, assumptions, and uncertainties involved in the methods of Drescher et al. We extend these results to incorporate other functional Knudsen Number dependencies and a quantum limit on $\eta/s$. [Preview Abstract] |
Thursday, October 15, 2009 11:15AM - 11:30AM |
CC.00009: Novel diagrammatic method for computing transport coefficients --- beyond the Boltzmann approximation --- Yoshimasa Hidaka, Teiji Kunihiro We propose a novel diagrammatic method for computing transport coefficients in relativistic quantum field theory. Our method is based on a reformulation and extension of the diagrammatic method by Eliashberg given in the imaginary-time formalism to the relativistic quantum field theory in the real-time formalism, in which the cumbersome analytical continuation problem can be avoided. The transport coefficients are obtained from a two-point function via Kubo formula. It is know that naive perturbation theory breaks down owing to a so called pinch singularity, and hence a resummation is required for getting a finite and sensible result. As a novel resummation method, we first decompose the two point function into the singular part and the regular part, and then reconstruct the diagrams. We find that a self-consistent equation for the two-point function has the same structure as the linearized Boltzmann equation. It is known that the two-point function at the leading order is equivalent to the linearized Boltzmann equation. We find the higher order corrections are nicely summarized as a renormalization of the vertex function, spectral function, and collision term. We also discuss the critical behavior of the transport coefficients near a phase transition, applying our method. [Preview Abstract] |
Thursday, October 15, 2009 11:30AM - 11:45AM |
CC.00010: Time-Dependent Variational Approach to the pure Gauge Theory for Evaluating the Shear Viscosity Yasuhiko Tsue, Tong-Gyu Lee, Hiroshi Ishii The time-dependent variational approach to the pure Yang-Mills gauge theory, especially a color $su(3)$ gauge theory, is formulated in the functional Schr\"odinger picture with a Gaussian wave functional approximation. The equations of motion for the quantum gauge fields are formulated in the Liouville-von Neumann form. This variational approach is applied in order to derive the shear viscosity, which is one of the transport coefficients for the pure gluonic matter, by using the linear response theory. As a result, the contribution to the shear viscosity from the quantum gluons is zero up to the lowest order of the coupling $g$ in the quantum gluonic matter. [Preview Abstract] |
Thursday, October 15, 2009 11:45AM - 12:00PM |
CC.00011: Non-collective component in v2 and how to detect it Jinfeng Liao Current RHIC data on elliptic flow v2 as a function of pT display dinstinctive patterns at low and high pT due to different sources of particle yield: the hydrodynamic collective flow dominating the low pT and the non-collective hard processes dominating the high pT. The intermediate region where v2 shows nontrival structure is yet not well understood. We emphasize the non-collective source which can also contribute to the observed v2 at low to intermediate pT. We further show that the backward-forward elliptic anisotropy correlation provides an experimentally accessible observable which distinguishes between collective and non-collective contributions to the observed v2. The measurement of this observable will reveal valuable information on the interpolation pattern at intermediate pT between the low-pT collective flow regime and the high-pT (semi)-hard processes regime. We also argue that the shift of dominance between the collective and non-collective sources is an alternative explanation to the dropping v2 at intermediate pT which may have important impact on quantifying the shear viscosity from v2 data. Reference: Jinfeng Liao \& Volker Koch, arXiv: 0902.2377. [Preview Abstract] |
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