Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session H10: Ultra-Relativistic Collisions |
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Sponsoring Units: DNP Chair: Thomas Ludlam, Brookhaven National Laboratory Room: Governor's Square 10 |
Sunday, May 3, 2009 10:45AM - 10:57AM |
H10.00001: Formation of Black Hole in AdS/CFT and Equilibration of QGP Shu Lin, Edward Shuryak It is believed that the Quark Gluon Plasma matter produced in heavy ion collision is strongly coupled. The application of AdS/CFT correspondence allows for analytical study of gauge field in strong coupling regime. A gravity dual of heavy ion collision was proposed by Shuryak et al The particles productions in the collisions are identified as creation of stringy debris in gravity. We studied the falling of different debris in AdS space. The backreaction of these debris to the AdS gravity are studied by solving linearized Einstein equation. We found the stress tensor did not adopt a hydrodynamics parameterization. We also used a simple gravitational collapsing model to study the equilibration of QGP. The model corresponds to the evolution of plasma to thermal equilibrium. We found interesting phenomenon of quasi-equilibrium: While the stress tenosor of equilibrating plasma is identical to plasma in thermal equilibrium, the spectral density differs by some oscillation. The spectral density shows a universal feature as the plasma equilibrates: the oscillation damps in amplitude and grows in frequency, eventually the plasma loses all the coherence. An attempt to understand the formation of QGP in AdS/CFT context was made by Gubser et al, where entropy was estimated as a function of energy in central collision of heavy ion. We extend the work to non-central collision, where we obtain the entropy as a function of impact parameter [Preview Abstract] |
Sunday, May 3, 2009 10:57AM - 11:09AM |
H10.00002: Measurement of Quark Transversity through the Collins Mechanism in Mid-Rapidity Jets in $p^\uparrow p$ Collisions at STAR Robert Fersch The spin-dependent azimuthal distribution of leading charged hadrons within jets resulting from transversely polarized $p^\uparrow p$ collisions can be expressed as a convolution of three different quantities. The first of these, the quark transverse spin distribution ($\delta q(x,Q^2)$), quantifies the probability of the quark spin aligning with the transverse spin of the proton. There is also dependence upon a hard-scattering spin-transfer coefficient calculated using pQCD (estimated as $\sim$0.5 in the STAR detector acceptance and trigger). Finally, there is a dependence on the Collins fragmentation function ($\Delta{D(z)}$), previously extracted from measurements made by the Belle, HERMES, and COMPASS collaborations. Measurement of the asymmetry in the reaction $p^\uparrow p \rightarrow$ jet $+\;X \rightarrow \pi + X$ should allow for an independent extraction of $\delta q(x,Q^2)$ via the same methods used in existing global analysis by Anselmino, et al. Transversely polarized ($\sim$58\%) $p^\uparrow p$ collision data ($\sim$1 pb$^{-1}$) at $\sqrt{s} = $200 GeV from the Solenoidal Tracker at RHIC (STAR) enable a statistically significant measurement of this asymmetry. The STAR detector provides full azimuthal coverage for both charged and neutral particle identification, and thus full jet reconstruction, in the mid-rapidity region ($|\eta|<1$). Progress toward measurement of this asymmetry for leading charged pions will be presented. [Preview Abstract] |
Sunday, May 3, 2009 11:09AM - 11:21AM |
H10.00003: Measurement of the Double Longitudinal Spin Asymmetry for Hadron Production in 200 GeV Polarized p+p Collisions at RHIC Bernd Surrow A primary goal of the STAR spin physics program at RHIC is the measurement of the gluon polarization, $\Delta g$, in the proton. The STAR detector, with its large-acceptance tracking and calorimetry, provides a uniquely suited environment for asymmetry measurements in a number of different final-state channels in polarized p+p collisions such as inclusive jet production, charged and neutral pion production. These asymmetries will provide important contributions to a global analysis of $\Delta g$. We present here the most recent measurements of the double longitudinal spin asymmetry ($A_{LL}$) for the production of charged and neutral pions at mid-rapidity. These asymmetries are compared to NLO pQCD calculations for different gluon polarization scenarios and are used to provide constraints on $\Delta g$. Charged pions are of particular interest as they are sensitive to the sign of $\Delta g$. Results and continuing analyses are presented from RHIC runs 5 and 6. [Preview Abstract] |
Sunday, May 3, 2009 11:21AM - 11:33AM |
H10.00004: Deep inelastic and dipole scattering on finite extent $\mathcal{N}$=4 SYM plasma Bowen Xiao, Alfred Mueller, Arif Shoshi Deep inelastic scattering of $\mathcal{R}$-currents and the scattering of a small dipole on finite length hot $\mathcal{N}$ =4 SYM matter are discussed. In each case we find the scale when scattering becomes strong is determined by a saturation momentum $Q^2_s \sim LT^3/x$ where $L$ is the length of the matter and $x=Q^2/2qT$. Using AdS/CFT correspondence, we calculate the structure function $F_i$ in finite length hot matter when $Q^2 \ll Q^2_s$. For infinite length matter the series generated by the OPE is not Borel summable but we are able to determine the exponential part of the tunneling amplitude determining $F_2$ when $\frac{Q^2}{Q^2_s}\gg 1$ from the position of the singularity closest to the origin on the real axis of the Borel plane. In finite length matter the OPE series is not convergent but it is Borel summable. When a small dipole of size $x_0$, and the string connecting the ends of the dipole, pass through hot matter there is an induced motion of the string in the $5^{th}$ dimension. We find that the energy of the string in the dipole rest frame gains a kinetic part($\textrm{KE}$) in addition to the Coulomb potential $\textrm{V}$. When $ T^4 L \gamma x_0^3\sim \mathcal{O}$(1), we find $E>0$ and there should be strong radiation and dipole dissociation which gives a limiting dipole size $x_L \simeq 1.1 \frac{1}{\pi T \left(\gamma \pi T L\right)^{1/3}}$ for a finite length plasma. [Preview Abstract] |
Sunday, May 3, 2009 11:33AM - 11:45AM |
H10.00005: Evaluation of the Underlying Event in pp collisions at $\sqrt{s} =$ 200 GeV at STAR Grant Webb The interpretation of STAR's published inclusive jet cross-section and longitudinal asymmetry data relies on a robust connection between the experimentally measured and theoretically calculated jet energy scale (JES). Evaluation of the underlying event (UE), the isotropic distribution of particles resulting from partonic interactions not associated with the inelastic collision producing the jet, is a necessary step in the quantification of the JES in hadronic collisions. This presentation will discuss progress toward the extraction of the UE in $\sqrt{s}=$ 200 GeV proton collisions produced at the Relativistic Heavy Ion Collider (RHIC) and detected in the Solenoidal Tracker at RHIC (STAR). Techniques, developed by the CDF collaboration at Fermilab, are used to isolate and charactertize the UE in dijet events. Comparisons between CDF and STAR results will be evaluated and progress towards quantifying the UE contribution to the JES for jets reconstructed at STAR will be reported. [Preview Abstract] |
Sunday, May 3, 2009 11:45AM - 11:57AM |
H10.00006: The STAR W Physics Program at RHIC Joseph Seele The STAR collaboration is preparing a tracking detector upgrade, the Forward GEM Tracker (FGT), which focuses on novel spin physics measurements in high-energy polarized proton-proton collisions, determining the flavor dependence ($\Delta \bar{u}$ versus $\Delta\bar{d}$) of the polarized sea. The production of $W^{-(+)}$ bosons provides an ideal tool to study the spin-flavor structure of the proton. $W^{-(+)}$ bosons are produced in $\bar{u}+d\,(\bar{d}+u)$ collisions and can be detected through their leptonic decays, $e^{-}+\bar{\nu}_{e}\,(e^{+}+\nu_{e})$, where only the respective charged lepton is measured. The sensitivity of those measurements is enhanced in the forward direction. The discrimination of $\bar{u}+d (\bar{d}+u)$ quark combinations requires distinguishing between high $p_{T}$ $e^{-(+)}$ through their opposite charge sign, which in turn requires precise tracking information. An upgrade of the STAR forward tracking system (FGT) is needed to provide the required tracking precision for charge sign discrimination. The FGT will consist of six triple-GEM detectors with two dimensional readout arranged in disks along the beam axis. Preparations are underway for the first collisions of polarized protons at a center-of-mass energy of $500\,$GeV in Run 9. The expected data sample will allow to study for the first time the collision of polarized protons mediated by W bosons at mid-rapidity prior to the anticipated installation of the FGT in summer 2010. The status of the FGT project together with plans for the first $500\,$GeV run in 2009 will be presented. [Preview Abstract] |
Sunday, May 3, 2009 11:57AM - 12:09PM |
H10.00007: The CMS ZDCs, from Beam Splash to Real Data F. Duane Ingram, Edwin Norbeck, Yasar Onel, Michael Murray, Oleg Grachov The CMS Zero Degree Calorimeters have been designed to measure forward photons and neutrons in proton-proton and heavy ion collisions. They are part of a large suite of forward detectors around the CMS interaction region. The ZDCs are also useful for beam tuning and luminosity measurements. The detectors were installed and ready for beam in the summer of 2008 and captured ``beam splash'' events on September 9th and 10th. We will present the status of the detectors and describe their physics capabilities, both singularly and in conjunction with other CMS detectors. [Preview Abstract] |
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