Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session GG: Ultrarelativistic Heavy Ions II |
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Sponsoring Units: DNP Chair: Charles Maguire, Vanderbilt University Room: Gaylord Opryland Hermitage D |
Saturday, October 28, 2006 9:00AM - 9:12AM |
GG.00001: Interference in vector meson production in Au + Au Collisions at $\sqrt{s}$ = 200 GeV from STAR Brooke Haag Photoproduction in Ultra Peripheral Collisions (UPCs) at the RHIC generates $\rho$ mesons. This occurs when a photon from one nucleus fluctuates into a quark-antiquark pair and scatters off the second nucleus producing a vector meson. The $t = p_T^2$ spectrum of the produced $\rho$ mesons, where t is the 4 momentum transfer squared, is sensitive to interference between the two possible production channels: the first nucleus emits a photon which scatters from the second nucleus, or vice versa. This interference is observed in the STAR data as a suppression in the $\frac {dN}{dt}$ spectrum at small t. In this talk, a measurement of the degree of interference will be presented as well as a discussion of systematic and statistical errors. [Preview Abstract] |
Saturday, October 28, 2006 9:12AM - 9:24AM |
GG.00002: Systematic uncertainties in heavy ion collision centrality measures Lanny Ray, Michael Daugherity The collision centrality for relativistic heavy-ion scattering events is often reported in terms of geometrical quantities using a model to relate the latter to multiplicity [1]. Using a Monte Carlo Glauber model the accuracy of several geometrical measures is reported for collision systems relevant to the RHIC program. The measures include impact parameter, number of interacting nucleons ($N_{part}$), number of binary interactions ($N_{bin}$), and the average number of binary collisions per incident participant nucleon $\nu = N_{bin}/(N_{part}/2)$ for Au-Au collisions at $\sqrt{s_{NN}}$ = 20, 62, 130 and 200 GeV and Cu-Cu at 62 and 200 GeV. Systematic uncertainties in the centrality measures due to errors in the matter densities, nucleon-nucleon cross section, multiplicity production model, and measured multiplicity frequency distribution are estimated. We find that the impact parameter is most accurately determined, followed closely by $\nu$. Centrality measures $N_{part}$ and $N_{bin}$ can be significantly affected by experimental uncertainties in the multiplicity frequency distribution [1], particularly that caused by trigger and primary vertex finding inefficiencies for low multiplicity events. Combined systematic errors for each collision system are given. \newline [1] C. Adler, et al., Phys. Rev. Lett. 87, 112303 (2001). [Preview Abstract] |
Saturday, October 28, 2006 9:24AM - 9:36AM |
GG.00003: Centrality dependence of thermal excitation-energy deposition in 14.6 GeV/c p+Au reactions and 8.0 GeV/c pbar/$\pi ^{-}$+Au reactions Ron Soltz Experiments E900 and E900a recorded data from proton, $\pi ^{-}$, and antiproton induced reactions on Au using the at the BNL AGS using the ISIS 4$\pi $ spectrometer. The energy and angular distributions for light-charged particles with E/A$\ge $8 MeV and intermediate mass fragements with 3$\le $Z$\le $16 were used to extract the excitation energy deposition for each event. We analyzed data for the highest energy runs of 8 and 14.6 GeV using protons with 30$\le $E$\le $350 MeV (grey protons) to extract the mean number of hadron-nucleon inelastic scatterings (nu) and the mean impact parameter (b) as a function of the grey track multiplicity. The analysis follows that of Experiment E910 and previous emulsion experiments of hadron-nucleus collisions in that an assumed distribution for the grey track multiplicity was convoluted with a glauber distribution and fit to the data. Systematic errors were estimated by varying the shape of the assumed distributions, the grey track cuts, and the hadron-nucleon cross-section of the glauber model. The thermal excitation-energy deposition will be presented as a function of the mean number of hadron-nucleon scatterings and the mean impact parameter. [Preview Abstract] |
Saturday, October 28, 2006 9:36AM - 9:48AM |
GG.00004: Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC Aneta Iordanova The charged particle multiplicity produced at RHIC will be presented as a function of collision energy, system size and geometry. The results will include d+Au, Au+Au and the recent Cu+Cu data. The data presented will utilize the unique, and nearly complete, solid angle coverage of the PHOBOS detector. With the data available, we will examine volume effects on the charged particle multiplicity to address global features of the particle production at RHIC energies. The data will be discussed in terms of collision geometry scaling of mid-rapidity yields and extended longitudinal scaling of the pseudo-rapidity density distributions. [Preview Abstract] |
Saturday, October 28, 2006 9:48AM - 10:00AM |
GG.00005: Energy Dependence of Short and Long-Range Multiplicity Correlations in Au+Au Collisions at RHIC Terence Tarnowsky Production of particles in the central rapidity region is dominated at all energies by short range correlations (SRC). Correlations that extend over a longer range are observed in high energy hadron-hadron interactions. Results from STAR for short and long-range multiplicity correlations (LRC) are presented for Au+Au collisions at $\sqrt{s_{NN}}$ = 200 and 62.4 GeV. These correlations are measured with an increasing gap in pseudorapidity ($\eta$), from no gap to a separation of 1.6 units. A suppression in the SRC strength near midrapidity is observed in central Au+Au data at 200 GeV. An increase in LRC are seen with larger $\eta$ gaps. For $p_{t} >$ 1 GeV, the suppression in SRC is diminished. This suppression of the SRC at midrapidity is not seen in Au+Au data at 62.4 GeV. Comparisons to HIJING and the Parton String Model (PSM) do not fully reproduce the central Au+Au data. String fusion as implemented in the PSM is one possibility that has been explored to understand the behavior seen in the data. This result may indicate a reduction of particle sources and possible formation of high density matter in central 200 GeV Au+Au collisions. [Preview Abstract] |
Saturday, October 28, 2006 10:00AM - 10:12AM |
GG.00006: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 10:12AM - 10:24AM |
GG.00007: Scaling properties of Elliptic Flow at RHIC energies Arkadij Taranenko Elliptic flow is one of the most sensitive probes to study the dynamical evolution and properties of the hot and dense medium created in ultra- relativistic heavy ion collisions at RHIC. One of the most important observations is the very good description of these measurements, up to $p_T$ ~ 1.5 GeV/c, by perfect fluid hydrodynamics, which predicts several scaling relations between elliptic flow and eccentricity, colliding system size, and transverse kinetic energy for different particle species. Testing these scaling predictions give the possibility to understand better the properties of the matter produced in heavy-ion collisions at RHIC. Detailed analysis of the scaling properties of the fine structure of elliptic flow at RHIC (i.e dependence on transverse momentum, particle type, centrality, system size, colliding energy...) will be presented and discussed. [Preview Abstract] |
Saturday, October 28, 2006 10:24AM - 10:36AM |
GG.00008: Elliptic Flow of Unidentified Hadrons at Forward Rapidity in 200GeV Au+Au collisions at RHIC Matthew Wysocki Elliptic flow ($v_{2}$) for different particles and in different regions of momentum space is a useful constraint on hydronamic models of heavy ion collisions at RHIC. Previous measurements of $v_{2}$ at forward rapidity in Au+Au collisions have been integrated over all $p_{T}$. Unidentified hadrons can be measured using the PHENIX Muon Spectrometers out to $|\eta|<2.0$, and their $v_{2}$ as a function of transverse momentum characterized. A description of the method for selecting hadrons is given, along with the most recent results. [Preview Abstract] |
Saturday, October 28, 2006 10:36AM - 10:48AM |
GG.00009: Centrality, p$_{T}$ and particle-type dependence of azimuthal anisotropy in Au+Au collisions at RHIC Yan Lu Anisotropy parameters (v$_{1}$, v$_{2}$, v$_{4}$, etc{\ldots}) carry information about interactions at early times in high-energy nuclear collisions. The systematic studies of azimuthal anisotropy may shed light on the relevant initial conditions, the degree of thermalization of the system, the equation of state, and the relevant degrees-of-freedom at the time that the momentum space anisotropy is established. In this talk, I present STAR measurements of identified particle v$_{2}$ and v$_{4}$ from low p$_{T}$ to high p$_{T}$ and as a function of collision centrality. These measurements will provide the most complete investigation of hadron-mass ordering, quark-number scaling and particle-type dependencies at very high momentum. Two important consequences indicated from the observation: (i) `collective flow' has developed prior to hadronization -- partonic collectivity at RHIC; (ii) partons are flowing in a volume that is much bigger than that of nucleons prior to hadronization. [Preview Abstract] |
Saturday, October 28, 2006 10:48AM - 11:00AM |
GG.00010: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 11:00AM - 11:12AM |
GG.00011: Forward-rapidity Elliptic Flow at RHIC S.J. Sanders, E.B. Johnson At RHIC energies large azimuthal anisotropies are observed in particle production with respect to the reaction plane for non-central heavy-ion collisions (i.e., azimuthal flow). Elliptic flow is measured by the 2$^{nd}$ harmonic (v$_{2})$ coefficient of the Fourier expansion of the azimuthal distribution. The observed anisotropies and the measured v$_{2}$(p$_{t})$ values suggest an almost perfect fluid state is created, consistent with the production of a quark-gluon plasma. Most measurements of identified-particle v$_{2}$(p$_{t})$ behavior at RHIC have been done near mid-rapidity, although a strong pseudorapidity dependence is seen for the charged-hadron, p$_{t}$-integrated v$_{2}$ values[1]. The interpretation of the integral v$_{2}$ data is complicated, however, by the rapidity dependent change in $<$p$_{t}>$ for each particle type. This talk will present new results of the BRAHMS experiment on $\pi $, K and p v$_{2}$(p$_{t})$ behavior at y $\approx $ 0, 1, and 3. The associated spectra will also be presented to help disentangle the kinematic factors affecting the integral v$_{2}$ values. These results can be used to better define the longitudinal expansion of the medium created through heavy-ion reactions at RHIC energies. [1] B.B. Back et al., PRL \textbf{94, }122303(2005). [Preview Abstract] |
Saturday, October 28, 2006 11:12AM - 11:24AM |
GG.00012: Elliptic Flow of Thermal Photons from Hydrodynamics E. Frodermann, U. Heinz, R. Chatterjee, D. Srivastava Anisotropic flow in non-central heavy ion collisions yields valuable constraints on dynamical models used to describe the evolution of the hot dense fireball. The elliptic flow of hadrons has been measured precisely, but hadrons only decouple from the thermal medium late in the evolution. Extracting information from hadrons about the QGP thus involves dynamical models. Photons, on the other hand, decouple from the medium upon creation, carrying information from the full fireball duration, particularly from the hottest early QGP stage. The flow pattern of direct photons should thus help to constrain dynamical models and the QGP equation of state especially during the early expansion stages. We calculate the elliptical flow of thermal photons in Au+Au collisions from a boost-invariant ideal hydrodynamical model. The photon elliptic flow decreases at high $p_T$ in contrast to the hadronic elliptic flow, reflecting the weak collectivity during the early QGP phase. We also point out an interesting structure at low $p_T$ which illuminates the dominating photon production channels in the late hadronic stage. [Preview Abstract] |
Saturday, October 28, 2006 11:24AM - 11:36AM |
GG.00013: $T-$Matrix Approach to Quarkonium Correlation Functions in the QGP Daniel Cabrera, Ralf Rapp We study the evolution of heavy quarkonium states with temperature in a Quark Gluon Plasma (QGP) by evaluating the in-medium $Q\bar{Q}$ $T-$matrix within a reduced Bethe-Salpeter equation in both $S-$ and $P-$wave channels. The underlying interaction kernel is extracted from recent finite-temperature QCD lattice calculations of the singlet free energy of a $Q\bar{Q}$ pair. The bound states are found to gradually move above the $Q\bar{Q}$ threshold after which they rapidly dissolve in the hot system. The $T-$matrix approach is particularly suited to investigate these mechanisms as it provides a unified treatment of bound and scattering states including threshold effects and the transition to the (perturbative) continuum. The $T-$matrix is then applied to calculate $Q\bar{Q}$ spectral functions as well as pertinent Euclidean-time correlation functions which are then compared to results from lattice QCD. The sensitivity to the interplay of bound and scattering states is found to be large. We furthermore investigate the impact of finite-width effects on the single-quark propagators in the QGP as estimated from recent applications of heavy-quark rescattering to RHIC data. [Preview Abstract] |
Saturday, October 28, 2006 11:36AM - 11:48AM |
GG.00014: Numerical Studies of Time-Dependent Relativistic Quantum-Machanical Systems Athanasios Petridis, Khinlay Win Using the numerical staggered leap-frog method the time-dependent, interacting Dirac equation is solved for a variety of systems. Specifically the relativistic decay of spinors initially set in potential wells constant in time is studied and found to exhibit strong non-exponential features as well as non-monotonic dependence on the potential strength. The relativistic decay of mesons is examined as they propagate through a medium in view of the recent Relativistic Heavy Ion data. The employed method is very stable and fast and is implemented on standard desk-top computers without loss of accuracy for both one and three-dimensional systems. [Preview Abstract] |
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