Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session C12: Ultrarelativistic Heavy Ions |
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Sponsoring Units: DNP Chair: Justin Frantz, Ohio University Room: A222-223 |
Saturday, April 14, 2018 1:30PM - 1:42PM |
C12.00001: Causal Charge Diffusion and Fluctuations in Heavy-Ion Collisions Christopher Plumberg, Joseph Kapusta We present a relativistic causal description of conserved-charge diffusion for heavy-ion collisions and show that it produces measurable effects in observables such as the charge balance functions. Other descriptions, based on ordinary diffusion, are known to produce charge fluctuations which propagate with infinite velocity, thus violating a fundamental postulate of special relativity. We present an alternative approach based on Cattaneo diffusion which restores relativistic causality, and show how to generalize this approach to dynamical, rapidly evolving systems such as heavy-ion collisions. We demonstrate that this approach leads to measurable consequences for the balance functions constructed from electrically charged hadrons in a simple 1+1 dimensional Bjorken hydrodynamic model. We find that limiting the speed of propagation of charge fluctuations increases the height and reduces the width of these balance functions when plotted versus separation in rapidity. We conclude by estimating the numerical value of the associated diffusion time constant from AdS/CFT. [Preview Abstract] |
Saturday, April 14, 2018 1:42PM - 1:54PM |
C12.00002: Response studies of the CME-sensitive sine observable to heavy ion backgrounds Yicheng Feng, Jie Zhao, Fuqiang Wang A new sine observable, $R(\Delta S)$, has been proposed to measure the Chiral Magnetic Effect (CME) in heavy ion collisions. Studies with A Multi-Phase Transport (AMPT) and Anomalous Viscous Fluid Dynamics (AVFD) models show concave $R(\Delta S)$ distributions for CME signals and convex ones for typical resonance backgrounds. A recent hydrodynamic study, however, indicates concave shapes for backgrounds as well. Preliminary STAR data, on the other hand, reveal concave $R(\Delta S)$ distributions in 200 GeV Au+Au collisions. To better understand these results, we present a systematic study of the $v_{2}$ and $p_{T}$ dependences of resonance backgrounds by toy-model simulations and Central Limit Theorem calculations. The resonance $v_{2}$ introduces different numbers of decay $\pi^+\pi^-$ pairs in the in-plane and out-of-plane directions. The resonance $p_{T}$ affects the opening angle of the decay $\pi^+\pi^-$ pair. For example, low $p_{T}$ resonances decay into large opening-angle pairs, result in more ``back-to-back'' pairs out-of-plane, mimicking a CME signal, or a concave $R(\Delta S)$. With these insights, we further investigate the responses of the $R(\Delta S)$ observable to AMPT backgrounds and AVFD CME signals, and the possible implications of the preliminary STAR data. [Preview Abstract] |
Saturday, April 14, 2018 1:54PM - 2:06PM |
C12.00003: Bulk viscosity of strongly interacting media: a dilepton perspective Gojko Vujanovic, Jean-Francois Paquet, Sangwook Ryu, Chun Shen, Gabriel Denicol, Sangyong Jeon, Charles Gale, Ulrich Heinz Recent viscous hydrodynamical studies of both photon [1] and hadron [2] observables at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC), show that bulk viscosity plays an important role in their phenomenological description. As bulk viscosity is a temperature-dependent quantity, it affects the development of the hydrodynamic momentum anisotropy differently in high- and low-temperature regions, thus also affecting anisotropic flow coefficients of different particles. Anisotropic flow coefficients of hadrons are sensitive to bulk viscosity at low temperatures of a hydrodynamical evolution, while dileptons are sensitive to all temperatures. Thus, bulk viscosity should affect dileptons and hadrons differently. This presentation studies how dilepton production gets modified owing to the presence of bulk viscosity at RHIC and LHC energies. Given the different collision energies (and thus temperatures) probed by RHIC/LHC, better conclusions regarding the role of bulk viscosity in high energy heavy-ion collisions can be drawn via comparisons of RHIC versus LHC results. \newline \newline [1] J.-F. Paquet et al., Phys. Rev. C 93, 044906 (2016) \newline [2] S. Ryu et al., Phys. Rev. Lett. 115, 132301 (2015) [Preview Abstract] |
Saturday, April 14, 2018 2:06PM - 2:18PM |
C12.00004: The static hard-loop gluon propagator to all orders in anisotropy Mohammad Nopoush, Yun Guo, Michael Strickland We calculate the (semi-)static hard-loop self-energy and propagator using the Keldysh formalism in a momentum-space anisotropic quark-gluon plasma. The static retarded, advanced, and Feynman (symmetric) self-energies and propagators are calculated to all orders in the momentum-space anisotropy parameter $\xi$. For the retarded and advanced self-energies/propagators, we present a concise derivation and comparison with previously-obtained results and extend the calculation of the self-energies to next-to-leading order in the gluon energy, $\omega$. For the Feynman self-energy/propagator, we present new results which are accurate to all orders in $\xi$. We compare our exact results with prior expressions for the Feynman self-energy/propagator which were obtained using Taylor-expansions around an isotropic state. We show that, unlike the Taylor-expanded results, the all-orders expression for the Feynman propagator is free from infrared singularities. Finally, we discuss the application of our results to the calculation of the imaginary-part of the heavy-quark potential in an anisotropic quark-gluon plasma. [Preview Abstract] |
Saturday, April 14, 2018 2:18PM - 2:30PM |
C12.00005: Bottomonium suppression at RHIC and LHC Brandon Krouppa, Alexander Rothkopf, Radoslaw Ryblewski, Michael Strickland Bottomonium suppression has long been discussed as a probe of quark-gluon plasma dynamics in ultra-relativistic heavy ion collisions and has been observed at both the LHC and RHIC particle accelerators. Using a realistic hydrodynamic background, we compute the suppression of bottomonium states and compare to data from STAR 200 GeV/nucleon and CMS/ALICE collisions, both at 2.76 TeV/nucleon and 5.02 TeV/nucleon collision energies. We find that models which incorporate in-medium suppression of heavy quark bound states can explain experimental observations reasonably well and that the level of suppression is incompatible with only cold nuclear matter effects. Recent work incorporates a lattice-vetted heavy-quark potential and regeneration effects on bottomomium states. [Preview Abstract] |
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