Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session DH: Ultra-Relativistic Heavy-Ion Collisions: Flow and Medium Response |
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Chair: Ivan Vitev, Los Alamos National Laboratory Room: Lamy |
Thursday, November 4, 2010 10:30AM - 10:42AM |
DH.00001: Multi-strange hadron elliptic flow in $\sqrt{s_{NN}}$ = 200 GeV Au + Au collisions at RHIC-STAR Hiroshi Masui Azimuthal anisotropy, especially for the multi-strange hadrons, is expected to reflect early dynamics in high-energy nuclear collisions. Due to the small hadronic cross section of multi-strange hadrons, their measured elliptic flow ($v_2$) carries information from the early partonic stages. We present the latest results of multi-strange hadron $v_2$ in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment at RHIC. The number of quark scaling for multi-strange hadron $v_2$ at intermediate $p_T$ and the possible breaking of mass ordering of the $\phi$ meson $v_2$ at low $p_T$ will be discussed. The data will also be compared with the results from an hybrid model combining ideal-hydrodymanics and hadronic-transport approaches. [Preview Abstract] |
Thursday, November 4, 2010 10:42AM - 10:54AM |
DH.00002: Scaling of Elliptic Flow, Recombination and Sequential Freeze-Out of Hadrons in Heavy-Ion Collisions Min He, Rainer Fries, Ralf Rapp The scaling properties of elliptic flow of hadrons produced in ultrarelativistic heavy-ion collisions are investigated at low transverse momenta. We reconfirm that the previously proposed Resonance Recombination Model converts the equilibrium quark distribution into equilibrated hadron spectra through coalescence. This enables a controlled extraction of quark distributions of the bulk matter at hadronization from spectra of multi-strange hadrons which are believed to decouple close to the critical temperature. The resulting elliptic flows from empirical fits at RHIC exhibit transverse kinetic-energy and valence-quark-number scaling. Utilizing the concept of sequential freeze-out the scaling at low momenta is shown to carry over to bulk hadrons ($\pi$, $K$, $p$) at thermal freeze- out, and thus results in an overall description compatible with both equilibrium hydrodynamics and quark recombination. [Preview Abstract] |
Thursday, November 4, 2010 10:54AM - 11:06AM |
DH.00003: Measurement of the $\phi$ meson production and azimuthal anisotropy in p+p and A+A collisions by STAR experiment at RHIC Maxim Naglis Enhanced strange particle production has been suggested as a diagnostic of hot and dense matter created in relativistic heavy ion collisions. Systematic measurements of strange particle yields and their azimuthal anisotropy as a function of transverse momentum, centrality, system size and collision energy provide a means for understanding the strangeness production in nucleon-nucleon and nuclei-nuclei collisions. Of particular interest have been the measurements of the $\phi$ meson, the lightest vector meson with net-strangeness zero and a mass similar to that of the proton and $\Lambda$. These unique features of the $\phi$ meson allow us to study many different aspects of the heavy ion collisions. This talk reviews the systematic measurements of $\phi$ meson production and azimuthal anisotropy in p+p, d+Au, Cu+Cu and Au+Au collisions at different energies performed at the STAR experiment, and discusses its implications. [Preview Abstract] |
Thursday, November 4, 2010 11:06AM - 11:18AM |
DH.00004: Directed and Elliptic Flow of Charged Hadrons in Cu+Cu Collisions at $\surd s_{NN }$= 22.4 GeV Yadav Pandit Measurements of anisotropic flow in heavy-ion collisions provide insight into the early stage of the system's evolution. Anisotropic flow is quantified by the Fourier coefficients $v_{n}$ of the distribution of particles with respect to the reaction plane. This talk reports recent results for directed ($v_{1})$ and elliptic flow ($v_{2})$ at $\surd s_{NN }$= 22.4 GeV. The measurements are based on the events at 0-60{\%} centrality for charged particles at mid-pseudo rapidity region \textit{$\vert \eta \vert $}$<$1.2 and at forward pseudorapidity region 2.5\textit{$<\vert \eta \vert <$}4.0 in the STAR experiment at RHIC. The STAR Beam Beam Counters (BBC) covering the pseudorapidity (\textit{$\eta $}) range 3.3 \textit{$< \quad \vert \eta \vert \quad <$ }5.0 with full azimuthal coverage are used to reconstruct the first-order event plane for the directed flow analysis. For the elliptic flow measurements, charged tracks in the time projection chamber are used to reconstruct the event plane. Comparisons with model calculations as well as with other methods and with different energies are presented. [Preview Abstract] |
Thursday, November 4, 2010 11:18AM - 11:30AM |
DH.00005: Investigaing the response of hot QCD matter to fast partons using bare thermal perturbation theory R.B. Neufeld The response of hot QCD matter to energetic partons has gained tremendous interest in light of two- and three- particle correlation measurements from heavy-ion collisions at RHIC that show a conical emission structure. While the association of this conical structure with Mach cone formation is uncertain, investigation of the medium response to fast partons is still very relevant. Within the perturbative framework, the traditional approach to such an investigation has been to treat the fast parton as a source of soft external color fields which perturb an otherwise thermal medium. In that approach, the appropriate formalism is the hard thermal loop effective theory. However, when the external fields generated by a fast parton are of the order of the temperature or higher, a different approach is needed. I will here present an approach for such a situation, in which bare thermal perturbation theory is used to evaluate the thermal average of the energy-momentum tensor. I will present results for components of the energy-momentum tensor for a gluonic medium in the presence of a fast parton. [Preview Abstract] |
Thursday, November 4, 2010 11:30AM - 11:42AM |
DH.00006: Asymmetric dihadron azimuthal correlations in Au+Au collisions at 200 GeV Joshua Konzer Dihadron correlations with high transverse momentum (pt) trigger particles provide a powerful tool to unravel the phenomena of the near-side long-range pseudorapidity correlation (ridge) and the away-side correlated conical emission (cone). Studies of dihadron correlations relative to the reaction plane have revealed intriguing dependencies of the ridge and possible Mach cone phenomena on the reaction plane. In this talk, we trigger on high-pt trigger particle orientations relative to the reaction plane, clockwise or counter-clockwise separately, and report dihadron correlations with those trigger particles for Au+Au collisions at 200 GeV. The results indicate a symmetric jet, an asymmetric ridge, as well as an asymmetric away-side correlation. We contrast our data to various theoretical models of the formation mechanisms of the ridge and cone phenomena, and discuss what we may learn from these data-model comparisons. [Preview Abstract] |
Thursday, November 4, 2010 11:42AM - 11:54AM |
DH.00007: ABSTRACT WITHDRAWN |
Thursday, November 4, 2010 11:54AM - 12:06PM |
DH.00008: Rapidity and $p_T$ distributions in pp at $\sqrt{s}=$ 62.4 and 200 GeV and comparison to pQCD and PYTHIA calculation Flemming Videbaek The BRAHMS experiment has measured minimum bias distributions of identified charged hadrons in pp collisions at $\sqrt{s}=$ 62.4 and 200 GeV at RHIC. The data obtained in 2005 and 2006 are compared to older measurements at ISR. Systematic features of rapidity distributions are presented, in particular those on net-protons and net-baryons. Extended longitudinal scaling is observed to hold up up to $\sqrt{s}=$ 200 GeV. The rapidity distributions are compared to PYTHIA, and an observations on different modern tunes are made. Net-proton distributions are poorly described in all cases raising the issue where underlying events may be different than min-bias and if models describing the central production region well are valid in the full rapidity range. Finally the high rapidity identified $p_T$ distributions are compared to NLO pQCD calculations. [Preview Abstract] |
Thursday, November 4, 2010 12:06PM - 12:18PM |
DH.00009: Azimuthal anisotropy: transition from hydrodynamic flow to jet suppression Roy Lacey The $2^{\rm{nd}}$ and $4^{\rm{th}}$ azimuthal anisotropy coefficients $v_{2,4}(N_{\rm{part}}, p_T)$ are scaled with the initial eccentricity $\varepsilon_{2,4}(N_{\rm{part}})$ of the collision zone and studied as a function of the number of participants $N_{\rm{part}}$ and the transverse momenta $p_T$. Scaling violations are observed for $p_T \alt 3$ GeV/c, consistent with a quadratic increase of viscous corrections with $p_T$. The predicted viscous corrections to flow and the thermal distribution function at freeze-out constrain estimates of the specific viscosity ($4\pi\frac{\eta}{s}$) to $1.1 \pm 0.1$ or $2.1 \pm 0.2 $ and the freeze-out temperature ($T_{\!f}$) to $162 \pm 11$ MeV or $173 \pm 11$ MeV for two different models for the initial collision geometry. For $p_T \agt 3$ GeV/c, the apparent viscous corrections exhibit a rapid decrease with $p_T$, suggesting a breakdown of the hydrodynamic ansatz and the onset of a change from flow-driven to suppression-driven anisotropy. [Preview Abstract] |
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