### Session KG: Relativistic Heavy Ions: Au+Au

 Thursday, September 22, 2005 2:00PM - 2:15PM KG.00001: PHENIX Measurement of Particle Yields at High pT with Respect to Reaction Plane in Au+Au collisions at $\sqrt{s}$ = 200 GeV David Winter One of the most intriguing puzzles in RHIC physics is the origin of the azimuthal anisotropy of particle yields at high pT ($>$ 5 GeV/c). Traditional flow and parton energy loss pictures have failed to describe the magnitude of this anisotropy. Measurement of the azimuthal asymmetry v2 at high pT will shed light on the contributions from flow, recombination, and energy loss, as well as the transition from soft to hard production mechanisms. The PHENIX Run4 dataset provides a powerful opportunity for exploring the angular anisotropy of identified particle yields at high pT. Complementing traditional v2 measurements, we present pi0 and eta yields as a function of angle with reaction plane, up to pT of at least 10 GeV/c. The centrality dependence of the angular anisotropy allows us to probe the density and path-length dependence of the energy loss of hard-scattered partons. We will discuss various mechanisms for particle production in this high pT region. Thursday, September 22, 2005 2:15PM - 2:30PM KG.00002: Transverse momentum distributions and string percolation study in p+p, d+Au, and Au+Au at 200 GeV Terence Tarnowsky , Brijesh Srivastava Multiparticle production at high energies is described in terms of color strings stretched between the projectile and target. These color strings hadronize, producing the observed particles. As string density increases, overlap among the strings leads to cluster formation. At some critical density a macroscopic cluster appears, spanning the entire system. This marks the percolation phase transition. Data from pp, d+Au and Au+Au at 200 GeV has been analyzed to experimentally determine the percolation density parameter, $\rho$. This value is obtained by parameterization of 200 GeV pp data. The resultant particle pt spectrum from pp collisions was fit with a power law. Values of the fit parameters are used in d+Au and Au+Au analysis. For 200 GeV Au+Au collisions, the value of $\rho$ is determined to lie above the critical percolation threshold. while for 200 GeV d+Au collisions it is below the critical value. This supports the idea of string percolation, which at high enough string density is a possible mechanism to explore the hadronic phase transition to a quark-gluon plasma (QGP). Thursday, September 22, 2005 2:30PM - 2:45PM KG.00003: Measurement of D* in Au+Au collisions at $\sqrt{s}$=200 GeV An Tai We present the status of the D* analysis in Au+Au collisions at $\sqrt{s}$=200 GeV. Comparisons with open charm production in d+Au collisions will be made. Implications on nuclear dependence of the charm quark yield and the nuclear modification factor of open charm production at intermediate $p_{T}$ will be discussed. Thursday, September 22, 2005 2:45PM - 3:00PM KG.00004: $R_{CP}$ measurement at forward rapidities with muons from light meson decays in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV in the PHENIX experiment at RHIC WooJin Park We study high pT light meson production at forward rapidity as a function of centrality in Au-Au collisions. It is expected that the energy and parton density of the fireball created in Au-Au collisions would be smaller at a larger rapidity, thus reducing the “jet quenching effects” observed at central rapidity for light mesons. On the other hand, gluon saturation models predict a suppression of particle yields at small x, or at a large rapidity, for a given pT. We perform a quantitative analysis of the nuclear modification factor $R_{CP}$ for high pT light mesons at forward rapidities in Au+Au collision at $\sqrt{s_{NN}}$=200 GeV. Light meson yields are measured in the PHENIX muon spectrometers through their decay muons. The latest results from this analysis will be presented. Thursday, September 22, 2005 3:00PM - 3:15PM KG.00005: $\phi \rightarrow K^{+}K^{-}$ meson measurements in d+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV Dipali Pal The $\phi$ meson is an important probe for studying both medium effects and strangeness production in high energy heavy ion collisions. In order to distinguish between cold and hot nuclear matter effects we compare the $\phi$ meson yields and line shapes in d+Au and Au+Au collisions at RHIC. The PHENIX experiment has measured the $\phi$ mesons in the $K^{+}K^{-}$ channel in both Au+Au and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV including the data from recent high statistics ($\sim$ 1.5 $\times$ $10^{9}$ events) in the RHIC 2003-4 run. The latest results on the $\phi$ meson line shapes and yields at different centralities will be discussed. Thursday, September 22, 2005 3:15PM - 3:30PM KG.00006: Photoproduction of $\rho$ mesons in Au+Au Ultra-Peripheral Collisions of $\sqrt{s_{NN}}$ = 200 GeV from STAR B.A. Haag Photoproduction between Au+Au ions in Ultra Peripheral Collisions (UPC's) at RHIC generates vector mesons including the $\rho$ meson. This occurs when a photon from one nucleus fluctuates into a quark-antiquark pair and scatters off the second nucleus which produces a vector meson. The $t$ = ${p_T}^{2}$ spectrum for $\rho$ production, 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. In this talk, we will present \textit{dN/dt} for $\rho ^{0 }$production from the STAR detector at RHIC. Correlations between the degree of interference and the features of the spectrum will be discussed. Thursday, September 22, 2005 3:30PM - 3:45PM KG.00007: Measurement of the low mass dielectron continuum in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions in the PHENIX Experiment at RHIC Ralf Averbeck Electromagnetic probes are ideally suited to investigate hot and dense matter produced in high energy heavy ion collisions. They do not undergo strong interactions and thus probe the full time evolution of the collision. The dielectron continuum is rich in physics. Dalitz decays of light hadrons and direct decays of vector mesons, which might be modified in the medium, and correlated charm decays contribute to the spectrum. Furthermore, exotic states, e.g quasi-particles predicted to exist in the medium only beyond the phase transition, might leave their footprint in the continuum. Although correlated e$^+$e$^-$ pairs are rare, the 0.24 nb$^{-1}$ collected by PHENIX for Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV in 2004 provides a significant sample to investigate the dilepton continuum. The continuum and its resonances are separated from the combinatorial background via an event mixing technique. Mass spectra are presented and compared with the expectations from decays of hadronic sources. Thursday, September 22, 2005 3:45PM - 4:00PM KG.00008: PHENIX Measurement of Azimuthally Sensitive Hanbury Brown-Twiss Interferometry in Au+Au Collisions at $\sqrt{s_{NN}}$=200GeV Jason Newby The initial spatial anisotropy of relativistic heavy-ion collisions with finite impact parameter has proven critical in understanding collision medium properties and system evolution. Nevertheless, our theoretical understanding remains incomplete and present hydrodynamic calculations are unable to simultaneously describe the experimentally observed elliptic flow and HBT radii. The Au+Au collisions recorded by the PHENIX experiment during the RHIC year 4 run provide a high statistics dataset to study observable trends in transverse momentum and collision geometry. We present an azimuthally sensitive measurement of the emitting source using Bose-Einstein correlations of identical charged pions. The excellent PHENIX particle identification provides sensitivity of extracted Bertsch-Pratt parameters across a broad range of pair transverse momentum essential for comprehensive evaluation of hydrodynamic calculations. Finally, we discuss promising experimental measurements of Bose-Einstein correlations with respect to the jet axis now possible at RHIC energies. Thursday, September 22, 2005 4:00PM - 4:15PM KG.00009: PHENIX Measurement of Charged Kaon Interferometry in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200GeV Akitomo Enokizono Detailed measurements of the Bose-Einstein correlations (HBT) of charged pions have revealed a fact that at RHIC energies the extents of source size and emission duration of charged pions were unexpectedly small and less changed from AGS energies. One of unresolved problems at RHIC is that such results are hard to be described by hydrodynamics calculations in conjunction with results of the single spectrum and elliptic flow of charged pions. Meanwhile, detailed studies of source sizes and emission durations of different particles are expected to give more insights in the freeze-out dynamics at RHIC. We present a HBT measurement of charged kaons by PHENIX in Au+Au collisions at $\sqrt{s_{NN}}$ = 200GeV. A high statistics data set taken during the Year-4 allows us to study the charged kaon source in several pair momentum and centrality regions. Both the recently developed imaging and a traditional HBT analysis schemes are applied to get detailed information of source functions and to compare with those of charged pions. Lastly, we discuss the possibility of measuring the space-time evolution of the source from photon correlations. Thursday, September 22, 2005 4:15PM - 4:30PM KG.00010: Methodology and Systematics for electron-hadron Correlations with the PHENIX Experiment at RHIC Jennifer Klay High $p_T$ electron-hadron correlations offer a way to study heavy flavor production in the complicated environment of relativistic heavy ion collisions. Near angle correlations can result from the semi-leptonic decays of D and B mesons while the correlation of an electron with an opposite side hadron is sensitive to the back-to-back jet signature of hard-scattered c and b quarks. To extract information about particles containing c- and b-quarks requires corrections for detector systematics as well as detailed understanding of background correlations arising from the anisotropic source, photon conversions and other hadronic decays. This talk will focus on the techniques used to evaluate these contributions to the electron-hadron correlation signals measured by the PHENIX experiment in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200GeV. Prospects for measuring e-h correlations with respect to the reaction plane will also be discussed. Thursday, September 22, 2005 4:30PM - 4:45PM KG.00011: PHENIX measurements on High $p_T$ photon-hadron and $\pi^0$-hadron Azimuthal Correlations in $\sqrt{s_{NN}}=200$~GeV Au+Au Collisions Jiamin Jin PHENIX has measured direct photon production in Au+Au collisions at $\sqrt{s_{NN}}=200$~GeV. Due to the suppression of high-$p_T$ pion production, a large photon excess over meson decay background is seen in central AuAu collisions at $p_T>6$GeV/c. This large direct photon signal allows us to use jets tagged by direct photons to probe the dense medium created in ultra- relativistic heavy-ion collisions at RHIC. Since photons interact with the medium much more weakly than hadrons, they will carry roughly the same amount of energy as the scattered quarks, thus providing a better measurement of the energy and direction of the away side jets. We will present the PHENIX results on the measurements of photon-hadron and $\pi^0$-hadron azimuthal correlations with the photon or $\pi^0$ momentum above 5 GeV/c. The results will be shown as a function of centrality and associated hadron $p_T$. By comparing the photon-hadron and $\pi^0$-hadron correlations, we will discuss the use of these two measurements to perform the first extraction of a direct photon-hardon correlation measurement at RHIC. Thursday, September 22, 2005 4:45PM - 5:00PM KG.00012: Strangelet Search at RHIC Aihong Tang It is demonstrated that strangelet production could be enhanced at forward region due to Pomeron cuttings[1]. We report the results of a strangelet search using a triggered data-set that sampled 60 million central (4\%) Au+Au collisions at the top RHIC energy of $\sNN= 200$~$GeV$ in the very forward rapidity region at the STAR detector. Two position sensitive Shower Maximum Detector (SMDs) were installed in the Zero-Degree Calorimeters (ZDCs) at STAR prior to run 2004. The calorimeters are located on both sides of the interaction point along the beam axis downstream of strong magnetic fields which sweep away particles with low rigidity. The ZDC-SMDs provide energy deposition as a function of transverse position in ZDCs. The strangelets, which have very large rigidities reflecting their large mass-to-charge ratios, are expected to produce an energy profile significantly different from neutrons. This is the first effort of strangelet search at RHIC, and also the first search at forward region. [1]M. Bleicher et al., Phys. Rev. Lett. 92 072301 (2004) Thursday, September 22, 2005 5:00PM - 5:15PM KG.00013: Preliminary Results on Direct Photon-Photon HBT Measurements in $\sqrt {s_{NN} }$=200 GeV Au+Au Collisions at RHIC Guoji Lin , Alexei Chikanian , Evan Finch , Jack Sandweiss , Haibin Zhang Direct photons emitted from the early hot phase of relativistic heavy ion collisions and their HBT correlations are an important signature of the quark gluon plasma and its properties. Despite the large number of decay photons, direct photon HBT correlations were observed at SPS energies[1]. Monte Carlo simulations at RHIC energies also show promising possibilities. In this presentation, we will report the current status on the direct photon HBT measurements in Au+Au collisions at $\sqrt {s_{NN} }$=200 GeV at STAR. Photons have been reconstructed using conversions via $\gamma \to e^+e^-$ in the STAR Time Projection Chamber (TPC) and energy deposited by photons in the STAR Barrel Electromagnetic Calorimeter (BEMC). Correlations have been extracted using one photon reconstructed from conversions and the other measured with the BEMC. Preliminary results of the two-photon correlation function distributions will be presented. Possible solutions to some difficulties we currently face and future plans will be addressed. [1]M.M Aggarwal et al.,Phys Rev. Lett. 93,022301(2004).