Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session HG: Ultrarelativistic Heavy Ions III |
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Sponsoring Units: DNP Chair: Julia Velkovska, Vanderbilt University Room: Gaylord Opryland Hermitage D |
Saturday, October 28, 2006 2:00PM - 2:12PM |
HG.00001: In-medium Modifications of Hadrons and the NA60 dimuon measurements Hendrik van Hees, Ralf Rapp The theoretical understanding of dimuon spectra as measured in 158~$A\,$GeV In-In collisions by the NA60 collaboration at the CERN SPS is summarized. The low-mass region, $M \leq 0.9 \; \mathrm{GeV}$, is well described by in-medium modifications of the $\rho$-meson spectral function within a hadronic many-body approach. To account for the yield in the intermediate-mass region, $0.9 \; \mathrm{GeV} \leq M \leq 1.5 \; \mathrm{GeV}$, four-pion contributions in the electromagnetic emission function have to be taken into account. The data are consistent with the assumption of chiral mixing of isovector-vector and -axialvector currents, which could be indicative for the onset of chiral-symmetry restoration in heavy-ion collisions. Our calculation also includes the contribution from the quark-gluon plasma phase which turns out to be small compared to that of the hadronic source. Predictions for the modifications of $\omega$- and $\phi$-meson spectral shape may be experimentally checked in future experiments. [Preview Abstract] |
Saturday, October 28, 2006 2:12PM - 2:24PM |
HG.00002: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 2:24PM - 2:36PM |
HG.00003: Probing Jet Topology with Multi-particle Correlations Nuggehalli Ajitanand Recent theoretical studies have indicated that jets can form a Mach cone like topology while traversing the low viscosity medium formed in the high energy Au+Au collisions at RHIC. Two particle azimuthal correlations are indicative of such a shape but can also be ascribed to away side jet deflection due to interactions with the strong flow field. Three particle correlations can distinguish between these scenarios. Use of a a high pT particle frame can enhance this capability. In this presentation results from the application of this method to simulations and RHIC 200 GeV Au+Au collisions will be shown. [Preview Abstract] |
Saturday, October 28, 2006 2:36PM - 2:48PM |
HG.00004: Two particle azimuthal correlations in $Cu+Cu$ collisions at $\sqrt{s_{NN}} = 200 GeV$ at RHIC Christine Nattrass Two particle correlations should yield information about jet quenching and production mechanisms at RHIC energies. They have already been studied extensively at RHIC in $Au+Au, d+Au$, and $p+p$ collisions at $\sqrt{s_{NN}} = 200 GeV $. Two particle azimuthal correlations in Cu+Cu collisions in the STAR detector at $\sqrt{s_{NN}} = 200 GeV $ using $\Lambda, \bar{\Lambda},$ and $K^0_S$ trigger particles are presented. Dependence of the near side peak on centrality and transverse momentum is investigated. Comparisons between baryons and mesons and between particles and antiparticles are made. [Preview Abstract] |
Saturday, October 28, 2006 2:48PM - 3:00PM |
HG.00005: Low- and intermediate-$p_T$ azimuthal di-hadron correlations from $\sqrt{s_{NN}}=200 \rm{GeV}$ central AuAu collisions measured in STAR Mark Horner Low- and intermediate-$p_T$ di-hadron correlations have already uncovered novel and exciting results at RHIC, tying together hard processes with bulk properties. We present systematic studies of di-hadron correlations for various trigger and associated $p_T$ selections, starting in the coalesence dominated region and extending up into the domain of fragmentation dominated triggers. We study the effects of varying the $\Delta\eta$- and $\Delta\phi$-integration windows within the STAR acceptance. The results are discussed in light of the interplay between radiative, hydrodynamic and recombination scenarios. [Preview Abstract] |
Saturday, October 28, 2006 3:00PM - 3:12PM |
HG.00006: ABSTRACT WITHDRAWN |
Saturday, October 28, 2006 3:12PM - 3:24PM |
HG.00007: Momentum dissipation and evolution of the bulk-medium produced in Au-Au collisions at RHIC Michael Daugherity A summary of two-particle number and transverse momentum ($p_t$) correlation results is presented which provides evidence for and properties of the highly dissipative medium formed in RHIC collisions. Large momentum scale two-particle correlation measurements in Au-Au collisions at $\sqrt{s_{NN}}$ = 130 GeV [1] have now been extended to 62 and 200 GeV, and to finer centrality bins. Number correlations on transverse momentum coordinates reveal strong momentum dissipation of low-$Q^2$ partons to the soft, bulk medium causing increased fluctuations. Similar correlation studies on pseudorapidity ($\eta$) and azimuth ($\phi$) indicate dramatic evolution of the same-side, low-$Q^2$ parton correlation peak with centrality. Net-charge correlations reveal a qualitative change of hadronization geometry from one-dimensional longitudinal fragmentation in p-p to two-dimensional bulk fragmentation in central Au-Au. Other features of the net-charge correlation data imply the development of an opaque medium. Transverse momentum correlations on $\eta,\phi$ suggest that the bulk medium recoils collectively in response to parton stopping. Current results will be shown and the data compared to Hijing and other model predictions. [1] J. Adams et al., Phys. Lett. B634, 347 (2006); nucl-ex/0411003; nucl-ex/0408012. [Preview Abstract] |
Saturday, October 28, 2006 3:24PM - 3:36PM |
HG.00008: Systematic Study of Di-Jet Shape Modification in hot QCD matter with the PHENIX detector Paul Constantin Experimental data collected at the Relativistic Heavy Ion Collider suggests the formation of a new state of dense deconfined QCD matter. One of the best tools to probe its properties is the study of its interaction with hard scattered partons that propagate through it. By using the method of di-hadron angular correlations, we study the shape modifications of hadronic di-jets produced from the fragmentation of such partons. We present a systematic study of the away-side ($\Delta\phi\sim\pi$) di-jet induced angular correlations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}} =$ 200 and 62 GeV in the intermediate (1-5GeV/c) transverse momentum region. [Preview Abstract] |
Saturday, October 28, 2006 3:36PM - 3:48PM |
HG.00009: Temperature uniformity of the bulk medium produced in relativistic heavy-ion collisions Lanny Ray The success of hydrodynamic models of elliptic flow in relativistic heavy ion collisions is often touted as evidence for rapid thermal equilibration. However, large momentum scale two-particle correlations indicate that a significant fraction of the final-state hadrons retain jet-like correlation structure associated with early stage, non-equilibrated low-$Q^2$ partons [1]. In addition, correlations on transverse momentum $(p_{t1} \times p_{t2})$ suggest that low-$Q^2$ parton momentum is partially dissipated causing fluctuations in the effective temperature (thermal and/or collective motion) of the bulk medium[2]. We first show that both global and local temperature fluctuation models describe the available $(p_{t1} \times p_{t2})$ correlation data equally well. Results of an analytical model are then presented which tests the sensitivity of $(p_{t1} \times p_{t2})$ correlations to the first few lower-order cumulants of the two-point temperature distribution for the event ensemble. Unique signatures in the predicted $(p_{t1} \times p_{t2})$ correlations are observed for each cumulant term studied. The prospects for direct measurement of the absolute temperature distribution in the bulk medium produced in relativistic heavy-ion collisions using $(p_{t1} \times p_{t2})$ and other correlation measures are discussed. [1] J. Adams et al., Phys. Rev. C {\bf 73}, 064907 (2006); J. Phys.G. {\bf 32}, L37 (2006). [2]J. Adams et al., nucl-ex/0408012. [Preview Abstract] |
Saturday, October 28, 2006 3:48PM - 4:00PM |
HG.00010: Study of dihadron fragmentation functions in $Au-Au$ at $\sqrt{s_{NN}} = 200 GeV $ collisions at RHIC as a probe of the medium Oana Catu Previous studies have shown jet modification in heavy ion collisions due to parton energy loss. One way to investigate this phenomenon is to study the dihadron fragmentation functions. In this work we use azimuthal correlations of high transverse momentum ($p_T$) hadrons to extract dihadron fragmentation functions. We study the correlations as a function of $p_T$ of the trigger and associated particles in $Au-Au$ collisions at $\sqrt{s_{NN}} = 200 GeV$ as measured in STAR. Earlier results showed that the ratio of opposite-sign pairs to same-sign pairs from Pythia simulations describe charge ordering in p-p collisions for lower $p_T$. We investigate charge ordering in heavy ion collisions and compare it to results from Pythia simulations. These new results will help gain insight into jet modification in the hot medium of high energy collisions, and hence put constraints on the nature and the magnitude of energy loss in this medium. [Preview Abstract] |
Saturday, October 28, 2006 4:00PM - 4:12PM |
HG.00011: Azimuthal $\gamma-h^{\pm}$ and $\pi^0-h^{\pm}$ jet correlations in 200 GeV CuCu collisions at RHIC Andrew Adare Azimuthal 2-particle jet correlations involving direct photons provide an important opportunity to study energy loss and jet fragmentation in the dense nuclear medium produced in heavy-ion collisions. A promising analysis technique is the statistical subtraction method, which involves obtaining direct $\gamma-h^{\pm}$ jet pairs by removing the decay component from inclusive $\gamma-h^{\pm}$ jet pairs. A description of this process is presented in addition to an update on recent results from the PHENIX experiment. [Preview Abstract] |
Saturday, October 28, 2006 4:12PM - 4:24PM |
HG.00012: The Impact Parameter Dependence of Heavy Ion Lepton Pair Production to All Orders in {\boldmath $Z \alpha$} Anthony J. Baltz The impact parameter dependence of the ultrarelativistic exact Dirac equation solution of heavy ion electron and muon pair production has been investigated. The exact formulation obtained differs from perturbation theory in such a way that the usual Feynman integral techniques cannot be used for the intermediate photon integral in the impact parameter dependent amplitude. Therefore a piecewise analytic numerical technique has been exploited. The total probability for electromagnetic pair production is found to be smaller than the pertubation theory result for both $e^+ e^-$ and $\mu^+ \mu^-$ pairs throughout the entire impact parameter range. This result may find application in heavy ion experimental conditions, where accepted events are triggered by zero degree calorimeter detection of neutrons from Coulomb dissocation. Detected pair production is thus more heavily weighted at small impact parameters. Predicted cross sections are then appropriately constructed from the integral of the product of the pair production probability times the dissociation probability. [Preview Abstract] |
Saturday, October 28, 2006 4:24PM - 4:36PM |
HG.00013: Fast Forward Calorimetry for CMS Jessica Snyder The CMS experiment at the LHC will study heavy ion and p-p collisions at 5 and 14 TeV respectively. The CMS heavy ion group has designed and built a Zero Degree Calorimeter (ZDC), to measure the topology of these collisions. This is part of a general effort in CMS to study low X physics and dense gluonic systems such as the Color Glass Condensate. The calorimeters are comprised of electromagnetic (EM) and hadronic sections with the Berkely shower maximum detector in between. The EM section is segmented transverse to the beam while the hadronic portion is segmented along the beam axis. For p-p collisions, we will study pomeron and odderon production since these are sensitive to the gluonic component of the proton wave function. For heavy ion collisions, we will measure the centrality of the events and provide a fast trigger for ultra-peripheral collisions. I will report on results from our recent beam test at CERN and extrapolate the ZDC's performance to LHC energies. [Preview Abstract] |
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