Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session R9: Ultrarelativistic Heavy Ions: Correlations, Spin |
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Sponsoring Units: DNP Room: Governor's Square 11 |
Monday, April 15, 2013 1:30PM - 1:42PM |
R9.00001: Long-Range Rapidity Correlations in Heavy-Light Ion Collisions Yuri Kovchegov, Douglas Wertepny We study two-particle long-range rapidity correlations arising in the early stages of heavy ion collisions in the saturation/Color Glass Condensate framework, assuming for simplicity that one colliding nucleus is much larger than the other. We calculate the two-gluon production cross section while including all-order saturation effects in the heavy nucleus with the lowest-order rescattering in the lighter nucleus. We find four types of correlations in the two-gluon production cross section: (i) geometric correlations, (ii) HBT correlations, (iii) back-to-back correlations, and (iv) near-side azimuthal correlations which are long-range in rapidity. The geometric correlations (i) are due to the fact that nucleons are correlated by simply being confined within the same nucleus and may lead to long-range rapidity correlations for the produced particles without strong azimuthal angle dependence. Somewhat surprisingly, long-range rapidity correlations (iii) and (iv) have exactly the same amplitudes along with azimuthal and rapidity shapes: one centered around $\Delta \phi =\pi$ with the other one centered around $\Delta \phi =0$ (here $\Delta \phi$ is the azimuthal angle between the two produced gluons). This prediction is in agreement with the recent ALICE p+Pb data. [Preview Abstract] |
Monday, April 15, 2013 1:42PM - 1:54PM |
R9.00002: Near- and Away-side Long-Range Angular Correlations in $d$+Au Collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV Michael McCumber Recent results from LHC experiments have demonstrated a near- and away-side excess that is present in central $p$+Pb collisions at $\sqrt{s_{_{NN}}}$ = 5.02 TeV. The pair-yield excess can be approximated by a second-order azimuthal modulation and has competing explanations from Color-Glass Condensate and hydrodynamic model calculations. The beam energy lever arm provided by comparison measurements at RHIC will aid in understanding the origin of these new measurements. To that end, we will present the results from a study of this phenomenon at the PHENIX detector in $d$+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. [Preview Abstract] |
Monday, April 15, 2013 1:54PM - 2:06PM |
R9.00003: A structure based study of initial state fluctuations in D-Au collisions Michael Kordell, Abhijit Majumder We study the spectrum and correlation between nucleon density fluctuations in the Au nucleus as probed in Deuteron(D)-Gold(Au) collisions at the Relativistic Heavy-Ion Collider (RHIC). Modeling the D with both hard sphere and Hulthen forms, we study the effect of various classical nucleon density distributions for the Au nucleus such as hard sphere, Gaussian and Woods-Saxon, as well as quantum distributions such as shell model based density distributions. Various means to incorporate the short distance hard sphere repulsion and resulting nucleon-nucleon correlation within shell-model based calculations will also be explored. In order to study initial state fluctuations, separated from any final state effects, we will focus on hard probes of initial density such as high transverse momentum hadron production in comparison with that from proton-proton collisions. Special emphasis will be placed on the new D-Au data from the PHENIX experiment at RHIC. [Preview Abstract] |
Monday, April 15, 2013 2:06PM - 2:18PM |
R9.00004: Angular distributions of partons inside the parton shower: from vacuum to dense QCD matter Ivan Vitev, Grigory Ovanesyan We study the angular distributions of next-to-leading order splitting functions describing the probability of one parton to branch into three partons. We perform this analysis for both vacuum splittings as well as splittings inside dense QCD matter. The motivation for this study is to numerically quantify to what extent the angular ordering phenomenon, which is widely used in parton shower generators in proton-proton collisions, is present both in vacuum and in dense QCD matter. We find unexpected results with important implications for QCD phenomenology. [Preview Abstract] |
Monday, April 15, 2013 2:18PM - 2:30PM |
R9.00005: Prompt photon measurements with the PHENIX MPC-EX detector Sarah Campbell The MPC-EX detector is a preshower extension to PHENIX's Muon Piston Calorimeter (MPC). It consists of eight layers of alternating W absorber and Si mini-pad sensors. Located at forward rapidity, $3.1<|\eta|<3.8$, the MPC and MPC-EX access low-x partons in the Au nucleus in p+Au collisions and high-x partons in the projectile in polarized p+p collisions. With the MPC-EX, photon and $\pi^{0}$ separation extends to $E>80$ GeV, allowing the measurement of prompt photons using the double ratio method. At forward rapidities, prompt photons are dominated by direct photons produced by quark-gluon Compton scattering. In transversely polarized p+p collisions, the prompt photon single spin asymmetry measurement, $A_{N}$, will resolve the sign discrepancy between the Sivers and twist-3 extractions of $A_{N}$. In p+Au collisions, the prompt photon $R_{pAu}$ will quantify the level of gluon saturation in the Au nucleus at low-x, $10^{-3}$, with a projected systematic error band a factor of four smaller than EPS09's current allowable range. The MPC-EX detector will expand our understanding of gluon nuclear parton distribution functions, providing information about the initial state of heavy ion collisions, and clarify how valence parton's $p_{T}$ and spin correlate to the proton spin. [Preview Abstract] |
Monday, April 15, 2013 2:30PM - 2:42PM |
R9.00006: Single Spin Asymmetries in polarized proton nucleus collisions with the MPC-EX detector Richard Seto The strength of transverse spin asymmetries in polarized proton nucleus collisions has been proposed as a~measure of the saturation scale. The RHIC facility is unique in its capability to provide the collisions of~transversely polarized protons on heavy nuclei for such studies.~ The existing PHENIX Muon-Piston Calorimeter (MPC)~ together with a new preshower extension - the MPC-EX - covers a~ pseudorapidity region 3.1 \textless \textbar $\eta $\textbar \textless 3.8 and is ideally suited for such studies. The combined detector system can identify neutral pions to high energy (80 GeV), direct photons, and charged tracks. This talk will cover the motivation and possible signatures which can be measured and the implications for gluon saturation. [Preview Abstract] |
Monday, April 15, 2013 2:42PM - 2:54PM |
R9.00007: Electromagnetic Dissociation at the Large Hadron Collider John Norbury Neutron production via electromagnetic dissociation in Pb-Pb collisions has recently been measured at the Large Hadron Collider (LHC). The very large experimental cross section of 196 barn is in excellent agreement with simple first order Weizsacker-Williams theory based on single photon exchange. The present work considers the effects of other corrections to Weizsacker-Williams theory such as electric quadrupole interactions, Rutherford bending of the beam trajectories, multiple photon exchange and strong interaction contributions to the total cross section. At LHC energies, it is found that all such corrections are negligible and this explains why the simplest Weizsacker-Williams theory is in excellent agreement with experiment. [Preview Abstract] |
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