Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session LD: Mini-Symposium: Probing the Ridge in Ultra-Relativistic Heavy Ion Collisions |
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Chair: Manuel Calderon, University of California at Davis Room: Jewett Ballroom G-H |
Sunday, October 26, 2008 8:30AM - 9:06AM |
LD.00001: Di-jet correlation tomography of ultrarelativistic nuclear collisions Invited Speaker: Moderate pT hadrons associated with quenched jets in ultrarelativistic nuclear collisions at RHIC exhibit a puzzling pattern of correlations as a function of rapidity and azimuthal angle (the near side rapidity Ridge the away side Mach like double shoulder features). These patterns are expected to provide detailed differential in pT information about the response of the strongly coupled Quark Gluon Plasma (sQGP) to rare but well calibrated high pT jets. This talk presents an overview of current pQCD and AdS/CFT jet tomography models and possible interpretations of these observations. [Preview Abstract] |
Sunday, October 26, 2008 9:06AM - 9:18AM |
LD.00002: Observation of a dramatic transition in the same-side $(\eta,\phi)$ correlation data from STAR Lanny Ray Two-dimensional angular correlations on relative pseudorapidity $\eta$ and azimuth $\phi$ are presented for charged particles from Au-Au collisions at $\sqrt{s_{NN}}$ = 62 and 200~GeV, with transverse momentum $p_t \geq 0.15$~GeV/$c$ and $|\eta| \leq 1$. Significant correlations are observed, including a peaked structure for same-side pairs (relative $\phi < \pi/2$) and a closely related away-side ridge. The same-side peak, associated with semihard parton scattering and fragmentation (minijets) in peripheral Au-Au and p-p collisions, follows binary-collision scaling in Au-Au collisions until mid-centrality where an abrupt transition to a qualitatively different centrality trend is observed. The transition (especially the large increase in $\eta$ width) leads to a manifestation at lower $p_t$ of the ridge phenomenon observed in trigger-associated particle correlations at higher $p_t$. Above the transition the number of same-side correlated particles increases rapidly relative to binary-collision scaling. The transition point at both energies occurs at a common transverse density of $\sim$2.5~particles/unit-$\eta$/fm$^{2}$. Our results contradict heavy ion collision scenarios which invoke rapid formation of an opaque, locally thermalized medium. [Preview Abstract] |
Sunday, October 26, 2008 9:18AM - 9:30AM |
LD.00003: Probing the medium response by two-particle correlations in Au+Au Collisions at $\sqrt{S_{NN}}$ = 200 GeV by the PHENIX Experiment Chin-Hao Chen PHENIX has measured the two-particle inclusive photon-hadron $\Delta\eta$-$\Delta\phi$ correlations at intermediate $p_T$. We decompose the away-side into a head region corresponding to the jet remnant which punches through the medium, and the shoulder, which contains the medium response. We report the per trigger yield of correlated particles in the two away-side components as well as in the trigger jet and near-side ridge in pseudorapidity. In order to study momentum flow between the jet and the medium, we weight the associated particle yields with transverse momentum, and compare the $p_T$ flow of the different components of the correlation function. [Preview Abstract] |
Sunday, October 26, 2008 9:30AM - 9:42AM |
LD.00004: Transition in same-side $(\eta,\phi)$ correlation for Cu-Cu data from STAR Duncan Prindle Two-dimensional angular correlations on relative pseudorapidity $\eta$ and azimuth $\phi$ are presented for charged particles from Cu-Cu collisions at $\sqrt{s_{NN}}$ = 62 and 200~GeV, with transverse momentum $p_t \geq 0.15$~GeV/$c$ and $|\eta| \leq 1$. For Au-Au data we observe a number of significant structures, including a peaked structure for same-side pairs (relative $\phi < \pi/2$) and a closely related away-side ridge. That peak follows binary-collision scaling in Au-Au until mid-centrality where an abrupt transition to a qualitatively different centrality trend is observed, leading to a manifestation at lower $p_t$ of the ridge phenomenon observed in trigger-associated particle correlations at higher $p_t$. Here we present results using the same analysis technique but on Cu-Cu collisions at $\sqrt{s_{NN}}$ = 62 and 200~GeV. Here we also observe a same-side peak and away side ridge. We focus on a comparison of the centrality trend of transition points in Cu-Cu to that of corresponding transitions previously observed in Au-Au. [Preview Abstract] |
Sunday, October 26, 2008 9:42AM - 9:54AM |
LD.00005: Onset of collective flow due to Weibel instabilities Jorgen Randrup, Stanis{\l}aw Mr{\'o}wczy{\'n}ski Since the local momentum density is highly anisotropic at the early stage of an ultra-relativistic nuclear collision, it is expected that Weibel instabilities will generate color currents with a characteristic (preferentially transverse) wave vector. As demonstrated first by Amp{\'e}re, different currents repel and in the SU(3) plasma there is therefore a net tendency for the Weibel currents to experience a mutual repulsion. This feature is phenomenologically important since the associated increase of the pressure provides a mechanism for the early development of collective flow. For the purpose of establishing a framework for examining this effect, we have extended our earlier work to encompass the evolving correlation function for the local momentum density. Starting from the fluctuations in a free gas of gluons, quarks and anti-quarks, we treat the self-consistent feed-back of the amplified chromodynamic fields on the phase-space densities. [Preview Abstract] |
Sunday, October 26, 2008 9:54AM - 10:06AM |
LD.00006: Measurements of Differential Transverse Momentum Correlation Function from the STAR Experiment Monika Sharma The event anisotropy measurements at RHIC have revealed that the
matter created in heavy ion collisions flows with very little
viscosity. The estimation of ``viscosity-to-entropy'' ratio is
currently a subject of extensive study [1]. In order to find
quantitative experimental information on the viscosity of the
medium we present measurements of differential transverse
momentum correlation function from the STAR experiment in $Au +
Au$ collisions at $\sqrt{s_{NN}} = $ 200 GeV. We study the
correlation function of the particles as a function of
pseudo-rapidity
and azimuthal angle in the range $0.2 |
Sunday, October 26, 2008 10:06AM - 10:18AM |
LD.00007: Constraining the Geometry to Study Jet Energy Loss with ``2+1'' correlations in PHENIX Hua Pei The RHIC at BNL collides heavy nuclei to create a medium at unprecedented density and temperature, commonly known as Quark Gluon Plasma (QGP). Jets of hadrons from quarks and gluons experiencing initial state hard scattering interact strongly with medium and provide a probe of transmission through the QGP that exists early in the collision. In back-to-back jets events, both partons survive to produce high-pt hadrons, and the distribution of hard-scattering locations is likely different than the surface-bias that affects single-particle studies, hence provide a better understanding of energy loss, and constrain the plasmas properties. Achieving these goals requires that we control the path-length traveled by the partons as much as possible and observables that are sensitive to the amount of energy loss of partons. We require a high-pt hadron in the back-hemisphere to the trigger particle, i.e., 2+1 particle correlations. We will present how correlations change as a function of these selection variables, and compare the Au+Au and Cu+Cu results with the baseline p+p results. [Preview Abstract] |
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