Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session LB: Ultrarelativistic Heavy-Ions II |
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Chair: Hirotsugu Fujii, University of Tokyo Room: Kona 4 |
Saturday, October 17, 2009 2:00PM - 2:15PM |
LB.00001: Two-dimensional charged particle correlations from 62 and 200 GeV Au+Au and Cu+Cu collisions from STAR Lanny Ray 2D angular correlations on relative pseudorapidity $\eta_{\Delta}=\eta_1-\eta_2$ and azimuth $\phi_{\Delta}=\phi_1-\phi_2$ are presented for charged particles with $p_t \geq 0.15$~GeV/$c$, $|\eta_{\Delta}| \leq 1$ and $2\pi$ in azimuth. A number of features are evident in the data including a 2D peak for small angle pairs and a ridge along $\eta$ at large azimuth. It is conjectured that both structures result from fragmenting, back-to-back semi-hard scattered partons, which follow binary scaling to mid-central collisions for each set of data. At a specific centrality, which varies with collision energy and ion, a transition to a qualitatively different trend is observed. This trend is characterized by rapidly increasing amplitudes, a much broader width on $\eta_{\Delta}$, and a reduced azimuth width for the small angle peak. Candidate scaling variables for the transition onset will be presented. These and other correlation data from STAR imply that correlated, low $p_t$ particles from fragmenting semi-hard scattered partons persist at RHIC energies, even in central collisions. The yields, including back-to-back processes, indicate relatively unsuppressed transport throughout the entire collision system, in strong contradiction with the expected attenuation of such processes in an opaque, thermalized medium. [Preview Abstract] |
Saturday, October 17, 2009 2:15PM - 2:30PM |
LB.00002: Two particle angular correlations in heavy ion collisions Siarhei Vaurynovich The nearly $4\pi$ angular acceptance of the PHOBOS silicon detector allows to perform measurements of 2-particle correlations over uniquely long distances in pseudorapidity with broad azimuthal angular coverage. Projections of the inclusive 2-particle angular correlation on the $\Delta\eta$ axis are studied in the context of a cluster model, allowing the extraction of the cluster size and decay width of the correlated particle production. This procedure reveals that particles are produced in very large clusters (up to an average size of around 6 charged particles) in the heavy ion collisions that were studied. Comparisons of the cluster size centrality dependence in Au+Au and Cu+Cu collisions demonstrate a scaling with the fractional cross section suggesting that the geometry of heavy ion collisions plays a significant role in the hadronization process. The high $p_{T}$-triggered correlations ($p_{T}>2.5$~GeV/c) are studied by comparing heavy ion collision data to p+p collisions simulated using PYTHIA, revealing in central Au+Au collisions an enhanced away-side yield much broader in $\Delta\phi$ and the presence of a near-side ``ridge'' extending continuously up to $\Delta\eta=4$. Comparison of the near-side correlated yield to PYTHIA suggests a decomposition into separate jet and ridge constituents, with the ridge yield having a significant centrality dependence. [Preview Abstract] |
Saturday, October 17, 2009 2:30PM - 2:45PM |
LB.00003: The ALICE EMCAL David Silvermyr The ALICE Electromagnetic Calorimeter (EMCAL) will provide the ALICE detector with enhanced jet triggering and reconstruction capabilities. This will allow detailed studies of the interaction and energy loss of high energy partons in the dense matter created in heavy ion collisions. The EMCAL consists of 12288 individual Pb-scintillator/shashlik towers grouped into 10 2/3 SuperModules. The detector thickness is approx. 20 X0 and the energy resolution has been measured to be better than 12\% ($\sqrt{E}$) + 2\%. The EMCAL's coverage will be 1.4 units in $\eta$ and 107 degrees in $\phi$ and it is positioned to provide partial back- to-back coverage with the PHOS calorimeter. The EMCAL will be installed in ALICE during the years 2009 - 2011, with four SuperModules ready for the first LHC 2009-2010 physics run. The detector status with a focus on readiness and plans for first physics measurements will be presented. [Preview Abstract] |
Saturday, October 17, 2009 2:45PM - 3:00PM |
LB.00004: Study of jet modification at LHC-ALICE Masato Sano ALICE is the experiment at CERN-LHC to study the property of quark-gluon-plasma (QGP) which is the QCD phase of matter at high temperature and density, and which is expected to be created by high energy heavy-ion collision. In heavy-ion collision, the initial hard scattered partons interact with the matter and loose its energy, and the effects appear as the modifications of the jet energy and structure compared to proton-proton collision. This means the jet modification can be a good probe to understand the property of QGP especially at CERN-LHC compared to BNL-RHIC because the jet production is significantly increase due to the higher collision energy. And jet tomography can be done by researching gamma/jet-hadron correlations. In this talk we report the capability of jet tomography at ALICE, comparing gamma/jet-hadron correlations in heavy-ion collision with the ones in proton-proton collision. [Preview Abstract] |
Saturday, October 17, 2009 3:00PM - 3:15PM |
LB.00005: Optimization of Jet Finding Algorithm in High energy heavy ion collisions with ALICE at LHC Dousatsu Sakata, Takuma Horaguchi The A Large Ion Collider Experiment (ALICE) is to study physics of strongly interacting matter and the quark-gluon plasma (QGP) in heavy ion collisions at Large Hadron Collider (LHC). Production of deconfined partonic phase has been basically proven at the BNL-RHIC, via high pt jet suppression. LHC will provide a high dence, high temperature and longer life time matter comparing with BNL-RHIC,therefore strong suppression and modification in jet production will be expected. A unified picture of jet quenching scenario is awaited at LHC-ALICE in wide energy range and various heavy ion collisions. However, jet finding in heavy ion collisions will be difficult at LHC due to the high multiplicity comparing with BNL-RHIC. Jet finding algorithm study for high multiplicity heavy ion collisions at LHC is so important. In this talk, we will present the results of comparison with some jet finding algorithms and study of the optimization of the algorithm for heavy ion collisions at LHC-ALICE. [Preview Abstract] |
Saturday, October 17, 2009 3:15PM - 3:30PM |
LB.00006: A light-front wavefunction approach to heavy quark dynamics in the QGP Ivan Vitev, Rishi Sharma, Benwei Zhang We calculate the charm and beauty fragmentation functions in the vacuum using their operator definitions in factorized perturbative QCD and find leading corrections that arise from the structure of the final-state hadrons. In the framework of potential models we demonstrate the existence of open heavy flavor bound states in the QGP in the vicinity of the critical temperature and provide first results for the in-medium modification of the heavy quark distribution and decay probabilities in a co-moving plasma. In an improved perturbative QCD description of heavy flavor dynamics in the thermal medium we combine D and B meson formation and dissociation with parton-level charm and beauty quark quenching to obtain predictions for the heavy meson and non-photonic electron suppression in Cu+Cu and Pb+Pb collisions at RHIC and the LHC, respectively. We discuss possible applications of this theoretical approach to the production of charmonium and bottomonium states in heavy ion reactions. [Preview Abstract] |
Saturday, October 17, 2009 3:30PM - 3:45PM |
LB.00007: ABSTRACT WITHDRAWN |
Saturday, October 17, 2009 3:45PM - 4:00PM |
LB.00008: J/$\psi$ production in minimum-bias d+Au collisions at $\sqrt{s_{NN}} = $200 GeV in STAR Christopher Powell The production of J/$\psi$ and other heavy quarkonia is of particular interest in relativistic heavy ion collisions, as their yields are supposed to be suppressed in the presence of the hypothesised hot, dense quark gluon plasma. However, there are other in-medium effects which will also suppress/enhance the production of J/$\psi$ (eg. Cronin effect, nuclear absorbtion and (anti-)shadowing effect). To understand the suppression and enhancement of heavy quarkonia in A+A collisions, we must first understand how yields are modified by a nuclear medium where no hot matter is present. Light systems such as p+p, p+A and d+A are particularly interesting as there are only cold nuclear matter effects present. We present the analysis of J/$\psi$ production in d+Au at $\sqrt{s_{NN}} = 200$ GeV (year 2008) with the STAR detector. Since this is the first run with a reduced amount of material in the centre of the detector (low material run), we expect a significant decrease in the number of background electrons as compared to previous runs. This provides a better handle on background and improves the signal quality. [Preview Abstract] |
Saturday, October 17, 2009 4:00PM - 4:15PM |
LB.00009: $J/\psi$ production in minimum bias Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV at STAR Daniel Kikola $J/\psi$ production is considered to be a sensitive probe of the properties of quark gluon plasma created in nucleus+nucleus collisions at RHIC. It has been studied in Au+Au and Cu+Cu collisions in the last years, and new Au+Au data taken by the STAR detector in year 2007 has recently become available, significantly improving statistics. In this presentation, the analysis of mid-rapidity($\left|y \right| < 1$) $J/\psi$ production via the dielectron decay channel in Au+Au(year 2007) and Cu+Cu(year 2005) collisions at $\sqrt{s_{NN}}=200$ GeV at STAR is reported. It is compared to STAR p+p results in order to study the nuclear modification factor as a function of transverse momentum and centrality. The results are compared to previously published data and available theoretical models. [Preview Abstract] |
Saturday, October 17, 2009 4:15PM - 4:30PM |
LB.00010: Quarkonia Melting in expanding hot and dense medium at RHIC Taku Gunji, Hideki Hamagaki, Tetsuo Hatsuda, Tetsufumi Hirano, Yukinao Akamatsu It is observed that $J/\psi$ production in Au+Au collisions at RHIC is stronly suppressed compared to the expectation from $p+p$ collisions. This may be the key to understand the properties of hot and dense medium created at RHIC since suppression would depend on the temperature of the medium and the size of $q\bar{q}$ system. One of the proposed scenarios is the sequential melting of charmonium states, where the absense of the feed down $J/\psi$ may occur just above the critical temperature ($T_{c}$) and melt of directly produced $J/\psi$ at much higher temperature. To study the sequential charmonia suppression in a dynamically evolving matter produced in Au+Au collisions at RHIC, we have recently developed a hydro+$J/\psi$ model. Melting temperatures of $J/\psi$, $\chi_c$ and $\psi~{\prime}$ are studied to describe momentum dependence and centrality dependence of the suppression and the results show melting temperature of $J/\psi$ can be determined around 2~$T_{c}$. Details of this model and results of the model calculations will be presented and discussed. [Preview Abstract] |
Saturday, October 17, 2009 4:30PM - 4:45PM |
LB.00011: Muons with High Transverse Momentum in IceCube Lisa Gerhardt Muons with a large transverse momentum ($p_{T}$) are produced in cosmic ray air showers via semileptonic decays of heavy quarks and the decay of high $p_{T}$ kaons and pions. These high $p_{T}$ muons will have a large lateral separation from the shower core. IceCube, a neutrino telescope consisting of a three-dimensional array of photodetectors buried in the ice of the South Pole and a surface air shower array, is well suited for the detection of high $p_{T}$ muons. The surface shower array can determine the energy, location and direction of the cosmic ray air shower while the in- ice array can do the same for the high $p_{T}$ muon. This makes it possible to measure the decoherence function (lateral separation spectrum) at distances greater than $\sim$150 meters. The muon $p_{T}$ can be determined from the muon energy (measured by dE/dx) and the lateral separation. The high $p_{T}$ muon spectrum may be calculated in a perturbative QCD framework; this spectrum is sensitive to the cosmic-ray composition. [Preview Abstract] |
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