Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session GD: Mini-Symposium: Cold Nuclear Matter and Low-x Physics at RHIC |
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Chair: Jamie Nagle, University of Colorado Room: Jewett Ballroom G-H |
Saturday, October 25, 2008 10:30AM - 11:06AM |
GD.00001: Physics of strong color fields at RHIC Invited Speaker: Nuclear collisions at RHIC provide a unique window into the properties of strong color fields. I will review the current state of knowledge about the nuclear wave functions at small Bjorken $x$ and the early moments of nuclear collisions with an emphasis on theory predictions for various experimental observables in Deuteron - Gold collisions. [Preview Abstract] |
Saturday, October 25, 2008 11:06AM - 11:18AM |
GD.00002: Charmonium production and absorption in proton-nucleus collisions Carlos Lourenco, Ramona Vogt, Hermine Wohri The $J/\psi$, $\psi'$ and $\chi_c$ yields are expected to be considerably suppressed if a deconfined medium is formed in high-energy heavy-ion collisions. However, already in $pA$ collisions the charmonium production cross sections scale less than linearly with the number of binary $NN$ collisions. This ``normal nuclear absorption'' must be accounted for before signals of the QCD medium can be identified in the $AA$ measurements. We compare the $J/\psi$ and $\psi'$ production in fixed-target $pA$ interactions ($200 < E_{\rm lab} < 920$~GeV) and in d+Au collisions at RHIC ($\sqrt{s}=200$~GeV) with Glauber calculations using several sets of \emph{nuclear} parton densities. We find a significant energy dependence of the mid-rapidity charmonium ``absorption cross sections'', indicating stronger nuclear absorption than previously assumed at $E_{\rm lab} = 158$~GeV, the CERN SPS lead beam energy. We also show that the absorption depends on the charmonium rapidity, even close to mid-rapidity. These new findings indicate stronger nuclear absorption than previously estimated from the SPS heavy-ion data. [Preview Abstract] |
Saturday, October 25, 2008 11:18AM - 11:30AM |
GD.00003: Charmonium Cold Nuclear matter effects: Unraveling a unique signature of the QGP Loren Linden Levy Charmonium suppression in hot and dense nuclear matter has been touted as an unique signature for the production of deconfined QCD matter. In order to search for this effect one must have a clear understanding of the modifications present in the charmonium spectrum resulting from the interaction with normal cold nuclear matter. The PHENIX collaboration has measured J/Psi spectrum from deuteron-gold (d-Au) interactions at $\sqrt{s}=$200GeV and compared these with a proton-proton baseline in order to constrain these cold nuclear matter effects. We will present the latest analysis from RHIC Run-8, with an integrated luminosity of ~80 nb$^{-1}$, compared to the 2.4 nb$^{-1}$ collected in RHIC Run-3. [Preview Abstract] |
Saturday, October 25, 2008 11:30AM - 11:42AM |
GD.00004: $J/\psi$ Measurements in A+A Collisions at PHENIX Matthew Wysocki $J/\psi$ production in A+A collisions is expected to be an important probe of the produced medium. Suppression due to color-charge screening was long expected to be a smoking gun for the quark-gluon plasma. However, in recent years a more complex picture of in-medium charmonium production and evolution has emerged, including cold nuclear matter (CNM) effects and enhancement from recombination of c-cbar pairs. At the same time, new experimental results that extend our reach in $p_T$ and new observables such as $v_2$ will allow us to better constrain theoretical models. The most recent $J/\psi$ results in $\sqrt{s_{NN}}$=200 GeV A+A collisions from the PHENIX experiment will be presented. By measuring these observables as functions of transverse momentum and rapidity PHENIX hopes to put quantitative constraints on the various effects that contribute to charmonium suppression in hot and dense QCD matter. [Preview Abstract] |
Saturday, October 25, 2008 11:42AM - 11:54AM |
GD.00005: Transverse energy in ultra-relativistic heavy ion collisions with the PHENIX MPC Brett Fadem The muon piston calorimeter (MPC), one of the detector upgrades to the PHENIX experiment, has only been in place since 2006. Consisting of two stations, North and South, the MPC significantly extends PHENIX's kinematic acceptance into the range $3.1<|\eta|<3.8$. In 2007, $\sqrt{s}$ = 200 GeV Au+Au collisions were produced at RHIC. Progress in measuring the transverse energy in the forward region of these collisions using the MPC will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 11:54AM - 12:06PM |
GD.00006: Are direct photons suppressed at high pT in relativistic heavy ion collisions? Gabor David Preliminary results from PHENIX on direct photon production in 200GeV Au+Au collisions indicated that while at moderate pT (4-14GeV/c) the nuclear modification factor for photons is unity, at higher pT it may be significantly less, maybe even similar to the well-established hadron-suppression (``jet quenching''). Such suppression might have both trivial reasons (``isospin effect'') and be the consequence of genuine nuclear effects. On the other hand this pT region is very challenging experimentally. Applying the latest analysis techniques to the 200GeV and 62GeV Au+Au data from PHENIX we will investigate if direct photons are suppressed at high pT and if so, what are the physics implications. [Preview Abstract] |
Saturday, October 25, 2008 12:06PM - 12:18PM |
GD.00007: Particle production at large Feynman-x in d-Au and p-p collisions at $\sqrt{s}$ = 200\,GeV Chris Perkins We report the status of the analysis of particle production in the pseudorapidity range $\eta$ = 2.5 to 4.2 using the Forward Meson Spectrometer (FMS) at STAR. The data used in this analysis were collected during the 2008 d-Au and p-p RHIC run at $\sqrt{s} = 200\,\mathrm{GeV}$. An integrated sampled luminosity of 50 nb$^{-1}$ (7.8 pb$^{-1}$) of d-Au (p-p) collisions were collected for this analysis. Particles are produced at large rapidity by asymmetric partonic collisions at this $\sqrt{s}$. This analysis focuses on pairs of clustered energy depositions in the FMS, arising primarily from incident photons, electrons and positrons. Of particular interest is the possible observation of J/Psi through its electron+positron decay. Event reconstructions are applied to both data and to full simulations using PYTHIA for event generation and GEANT for detector response, and then intercompared. Observation of large $x_F$ J/Psi production is of interest because of the possibility that intrinsic charm components in the proton wave function contribute to its production. [Preview Abstract] |
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