Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session EG: Ultra Relativistic Heavy Ion Collisions II |
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Chair: Helen Caines, Yale University Room: Newport News Marriott at City Center Pearl Salon III |
Friday, October 12, 2007 2:00PM - 2:12PM |
EG.00001: Heavy quark energy loss in a dynamical QCD medium Magdalena Djordjevic, Ulrich Heinz The computation of radiative energy loss in a dynamically screened QCD medium is a key ingredient for obtaining reliable predictions for jet quenching in ultra-relativistic heavy ion collisions. We calculate, to first order in the opacity, the energy loss suffered by a heavy quark traveling through an infinite and time-independent QCD medium and show that the result for a dynamical medium is almost twice that obtained previously for a medium consisting of randomly distributed static scattering centers. A quantitative description of jet suppression in RHIC and LHC experiments thus must correctly account for the dynamics of the medium's constituents [1]. \newline [1] M. Djordjevic and U. Heinz, arXiv:0705.3439 [nucl-th] [Preview Abstract] |
Friday, October 12, 2007 2:12PM - 2:24PM |
EG.00002: Measurement of the D meson Production through Hadronic Decay Channel at PHENIX Sergey Butsyk The Open Charm production have always been considered as one of the unique and unbiased probes to study the properties of the dense matter produced in Heavy Ion collisions at RHIC. PHENIX experiment at RHIC has done a tremendous job of measuring the production rate of the Heavy Flavor particles through their semi-leptonic decay channels. By studying the production in a different colliding systems (p+p, d+Au, Au+Au) we were able to separate both initial and final state effects in nucleon+nucleon collisions at 200 GeV/N. The unanswered question for those measurements was a relative contribution of Open Charm to the mixture of Open Charm and Open Bottom particle decays that were accessible experimentally in semi-leptonic channel. The first results of the direct measurement of D meson production in proton+proton collisions through the hadronic decay channel will be presented. This measurement will should determine the contribution of the Open charm to the mix and also constrain the theoretical models for the Open Charm production at RHIC energies. The current status of analysis, as well as comparison with the most resent theoretical predictions will be presented. [Preview Abstract] |
Friday, October 12, 2007 2:24PM - 2:36PM |
EG.00003: Measurement of the Open Charm Cross Section in $\sqrt{s_{NN}}$ = 200 GeV Cu+Cu Collisions for the STAR Experiment at RHIC Stephen Baumgart Because charm is produced during initial gluon fusion it provides a good probe of the early stages of the matter produced in a relativistic heavy ion collision. Deviations from theoretical predictions for heavy ion collisions may show medium effects. STAR has measured charm production in p+p, d+Au, and Au+Au collsions at $\sqrt{s_{NN}}$ = 200 GeV using semi-leptonic decay channels and in d+Au and Au+Au collsions at $\sqrt{s_{NN}}$ = 200 GeV using the $D^{0} \rightarrow K\pi$ channel. We report on the measurement of $D^{0} \rightarrow K\pi$ in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV. A transverse momentum spectrum will be shown as well as the extrapolated open charm cross section. The charm cross section in Cu+Cu will be compared to previous experimental results as well as to FONLL theoretical predictions. [Preview Abstract] |
Friday, October 12, 2007 2:36PM - 2:48PM |
EG.00004: D0 measurements in Cu+Cu collisions at sqrt(s)=200 GeV Sarah LaPointe The heavy quark production in relativistic heavy ion collisions provides a reference for heavy meson formation, energy loss and collectivity of heavy quarks in nuclear medium. In this talk, we present preliminary results from D0 measurements in minimum bias Cu+Cu collisions at sqrt(s)=200 GeV. The measurements are performed using an exploratory analysis trying to optimize secondary vertexing. This provides a basis for future measurements of heavy quark energy loss and collectivity in heavy ion collisions at RHIC. [Preview Abstract] |
Friday, October 12, 2007 2:48PM - 3:00PM |
EG.00005: Two-component approach to $J/\psi$ $p_t$-Spectra at SPS and RHIC Xingbo Zhao, Ralf Rapp We investigate $J/\psi$ transverse-momentum distributions as well as their centrality dependence in Pb-Pb collisions at SPS and Au-Au collisions at RHIC within the framework of a two-component model, which includes (i) a primordial contribution coupled with various phases of dissociation, (ii) a statistical coalescence of $c$ and $\bar{c}$ quarks at the hadronization phase transition. We use a transport equation combined with expanding fireball equations to study the component (i) and use a blast-wave approach to study the component (ii). The influence of various physical mechanisms on the $J/\psi$ $p_t$ distributions are investigated, together with applications to experimental data. [Preview Abstract] |
Friday, October 12, 2007 3:00PM - 3:12PM |
EG.00006: Determining Relative Contributions of Charm and Bottom to Single Electron Spectra in pp Collisions at RHIC Harry Themann Heavy quark production has always been considered as one of the unique and unbiased probes to study the properties of the dense matter produced in Heavy Ion collisions at RHIC. The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) with its exceptional electron identification system enables us to perform high precision measurements of electron yields. By measuring electron production at high transverse momentum, we can disentangle the contribution of electrons originating from semi-leptonic decays of heavy quarks (charm or bottom) from the less interesting ``photonic" decay modes of light mesons. The ability to disentangle the relative contribution of charm and beauty to the electron yield has not been available. We have combined the data of the 200GeV pp Run 5 with Run 6. This combination allows the electron p$_{T}$ spectrum to be extended to at least 10 GeV where the contribution from bottom is expected to dominate. We compare these spectra to pQCD calculations to attempt to quantify the relative contributions of charm and bottom. [Preview Abstract] |
Friday, October 12, 2007 3:12PM - 3:24PM |
EG.00007: High-$p_T$ $J/\Psi$ production in p+p collisions at $\sqrt{s}$=200 GeV Zebo Tang, Lijuan Ruan, Zhangbu Xu We report our preliminary analysis of high-$p_T$ $J/\Psi \rightarrow e^+e^-$ production at $p_T \sim 6$ GeV/c at mid-rapidity in p+p collisions at $\sqrt{s}$=200 GeV. The datasets are from RHIC run V and VI, sampling more than a few hundreds(nb)$^{-1}$ of p+p collisions in a trigger on energy deposit in Electromagnetic Calorimeter with energy threshold of $\sim>$2.6GeV. This provides a baseline for future study of $J/\Psi$ suppression at high-$p_T$ in heavy-ion collisions at RHIC. [Preview Abstract] |
Friday, October 12, 2007 3:24PM - 3:36PM |
EG.00008: Beam Energy and System Size Dependence of Dynamical Netcharge Fluctuations Monika Sharma, Claude Pruneau, Sergei Voloshin, Madan Aggarwal, Gary Westfall, Bedanga Mohanty We present measurements of net charge fluctuations in Au + Au collisions at $\sqrt{s_{NN}} = $ 20, 62.4, 130, and 200 GeV, Cu + Cu collisions at $\sqrt{s_{NN}} = $ 62.4, 200 GeV, and p + p collisions at $\sqrt{s_{NN}} = $ 200 GeV, using the net charge dynamical fluctuations measure $\nu_{+-,dyn}$. We observe the dynamical fluctuations are finite at all energies and exhibit a rather modest dependence on beam energy. We also observe weak system size dependence. We examine the collision centrality dependence of the net charge fluctuations and find net charge violate the trivial $1/N_{CH}$ scaling expected for nuclear collisions consisting of independent nucleon-nucleon interactions but however display $1/N_{part}$ scaling. We also studied the azimuthal and rapidity dependence of the net charge correlation strength and observed strong dependence on the azimuthal angular range and pseudorapidity bins integrated to measured the correlation. We argue this dependence may arise due to large radial flow. [Preview Abstract] |
Friday, October 12, 2007 3:36PM - 3:48PM |
EG.00009: Transverse momentum broadening of vector bosons in nuclear collisions Zhong-Bo Kang, Jian-Wei Qiu We calculate in perturbative QCD the transverse momentum broadening of vector bosons in nuclear collisions. We evaluate the effect of initial-state parton multiple scattering for the production of Drell-Yan and $W/Z$ bosons, and both initial- and final-state multiple scattering effect for heavy quarkonium production. We predict the transverse momentum broadening of $W/Z$ bosons in heavy ion collisions at the LHC energies, and argue that the broadening should be a clean probe of initial-state medium effect [1]. For heavy quarkonium production, we found in both NRQCD and Color Evaporation model that the transverse momentum broadening of heavy quarkonia in hadron-nucleus collision is close to $2C_A/C_F$ times the corresponding Drell-Yan broadening, which is consistent with Fermilab E866 data [1]. We also predict a significant reduction of the transverse momentum broadening for heavy quarkonia in relativistic heavy ion collisions if a dense medium is formed. \newline [1] Z.~B.~Kang and J.~W.~Qiu, arXiv: 0707.0276 [hep-ph] [Preview Abstract] |
Friday, October 12, 2007 3:48PM - 4:00PM |
EG.00010: Physics with the PHENIX muon trigger upgrade Brett Fadem The upgrade of the PHENIX first level muon trigger will consist of new muon tracker front end electronics and a new dedicated trigger spectrometer with three resistive plate chambers stations in each PHENIX muon arm. This will make it possible to efficiently trigger on those polarized proton-proton collisions that result in the formation of a W-boson. PHENIX will use this capability to obtain spin sorted measurements of the charge dependent yields of W bosons. These measurements will allow us to determine flavor-separated quark and anti-quark polarizations in the proton. [Preview Abstract] |
Friday, October 12, 2007 4:00PM - 4:12PM |
EG.00011: Pixel telescope test in STAR at RHIC Xiangming Sun, Michal Szelezniak, Leo Greiner, Howard Matis, Chinh Vu, Thorsten Stezelberger, Howard Wieman The STAR experiment at RHIC is designing a new inner vertex detector called the Heavy Flavor Tracker (HFT). The HFT's innermost two layers is called the PIXEL detector which uses Monolithic Active Pixel Sensor technology (MAPS). To test the MAPS technology, we just constructed and tested a telescope. The telescope uses a stack of three MIMOSTAR2 chips, Each MIMOSTAR2 sensor, which was designed by IPHC, is an array of $132\times128$ pixels with a square pixel size of $30 \mu$. The readout of the telescope makes use of the ALICE DDL/SIU cards, which is compatible with the future STAR data acquisition system called DAQ1000. The telescope was first studied in a 1.2 GeV/c electron beam at LBNL's Advanced Light Source. Afterwards, the telescope was outside the STAR magnet, and then later inside it, 145 cm away from STAR's center. We will describe this first test of MAPS technology in a collider environment, and report on the occupancy, particle flux, and performance of the telescope. [Preview Abstract] |
Friday, October 12, 2007 4:12PM - 4:24PM |
EG.00012: Heavy Flavor Measurements with FVTX Upgrade Detector at PHENIX Sergey Butsyk The Relativistic Heavy Ion Collider at Brookhaven National Laboratory opened a new era in Heavy Ion Physics. Measurement of heavy flavor (charm and bottom) production at RHIC is one of the most important goals of the RHIC physics program. Open Charm and Bottom is born in the early stages of the collision and carries the full information about the evolution of the collision. Over the last 6 years the PHENIX experiment has developed techniques for disentangling the yield of muons from heavy flavor particles from the single muon spectrum. However, this analysis relies on the precise knowledge of the background muon sources: muons from hadronic decays and punch-through hadrons that pass through the material of absorber. Large systematical errors come from poor knowledge of the background muon sources. To significantly improve the current heavy flavor program in muon channel PHENIX plans to construct a Forward Vertex Detector, consisting of four disks of silicon strips in the muon arm acceptance and install it by Year 2011. I would like to describe the physics goals for the proposed upgrade and to present the current expectations for the background rejection improvement for the heavy flavor measurenent with FVTX detector. [Preview Abstract] |
Friday, October 12, 2007 4:24PM - 4:36PM |
EG.00013: Heavy Flavour and calibration of the STAR Preshower Calorimeter Rory Clarke Heavy flavour quarks provide a unique probe into the hot dense deconfined medium expected to form during heavy ion collisions, the Quark Gluon Plasma. One of the signals of this state of matter is the suppression of the J/Psi signal, observed in PHENIX and the SPS. However, this is complicated by the recombination of charm quarks in the medium. A possible signal that would not undergo recombination is the Upsilon and this could be used to compliment the J/Psi signal. The wide opening angle of the dilepton decay channel makes the large acceptance of the STAR detector ideal for reconstructing this signal. The preshower detector is part of the STAR Barrel Electromagnetic Calorimeter (BEMC). The calorimeter surrounds the STAR tracking chamber and measures particle energies via secondary showers that pass though it. The preshower detects the early showering of electrons, which can then be separated from later interacting hadrons. The setup will be discussed along with a tour of the methods used to calibrate signals from this detector. Finally, the increased hadron rejection possible from this detector will be discussed for heavy flavour programs being conducted at RHIC, such as the Upsilon and J/Psi searches. [Preview Abstract] |
Friday, October 12, 2007 4:36PM - 4:48PM |
EG.00014: Electron identification at STAR and the Barrel Preshower detector Matthew Cervantes The Barrel Electromagnetic Calorimeter (BEMC) in the STAR experiment at RHIC is a sampling lead scintillator consisting of 4800 towers. The data from the first 2 layers of each tower is read out separately and formally defines the Barrel Preshower (BPRS) detector. The BPRS distinguishes between electrons developing a shower early in the calorimeter tower as opposed to interactions that occur beyond these first 2 layers. We will report on the commissioning of the BPRS into the STAR detector and its implementation into an electron-based analysis. We present the standard method of particle identification currently used for electron selection and investigate the effect of using the BPRS detector. Comparison of such an analysis with and without the BPRS will be shown. [Preview Abstract] |
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