Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session S12: MiniSymposium on Initial State and Earlytime Dynamics of Heavy Ion Collisions IMiniSymposium

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Sponsoring Units: DNP Chair: Julia Velkovska, Vanderbilt University Room: A222223 
Monday, April 16, 2018 1:30PM  2:06PM 
S12.00001: The initial state and early time dynamics in heavyion collisions Invited Speaker: Ronald Belmont The standard picture of heavy ion collisions is that large systems (collisions of large nuclei like Au+Au and Pb+Pb) create a quarkgluon plasma that exhibits collective behavior indicative of nearly inviscid hydrodynamical evolution. Recently, data from small systems (collisions of a small projectile and a large target like d+Au and p+Pb) have been found to exhibit strikingly similar evidence for collective behavior. Contrariwise, while there is a wealth of evidence for particle suppression and jet attenuation in large systems, such effects are notably absent in small systems. In this talk we give an introduction to the initial state and early time dynamics of heavy ion collisions, giving an overview of results in large and small systems. [Preview Abstract] 
Monday, April 16, 2018 2:06PM  2:18PM 
S12.00002: (3+1)D Viscous Anisotropic Hydrodynamics for Nonconformal Fluids Michael McNelis, Ulrich Heinz, Dennis Bazow Anisotropic hydrodynamics improves upon standard viscous hydrodynamics by treating certain large dissipative corrections nonperturbatively. Relativistic heavyion collisions feature two such large viscous effects: (i) Strongly anisotropic expansion along the beam direction generates a large shear stress, leading to very different longitudinal and transverse pressures at early times. (ii) Critical fluctuations near the quarkhadron phase transition lead to a large bulk pressure on the conversion surface between hydrodynamics and a hadronic cascade description of the final collision stage. We present a new dissipative hydrodynamic formulation for nonconformal fluids where both of these effects are treated nonperturbatively using an anisotropic leadingorder distribution function with two momentumspace deformation parameters. Generalized Landau matching conditions are required to fix these parameters, accounting for the longitudinal and transverse pressures. Residual shear stresses are treated perturbatively, as in standard viscous hydrodynamics. The resulting hydrodynamic evolution equations are derived from the Boltzmann equation in 3+1 dimensions and tested in a (0+1)dimensional Bjorken expansion. Comparisons with viscous hydrodynamical frameworks are presented. [Preview Abstract] 
Monday, April 16, 2018 2:18PM  2:30PM 
S12.00003: Anisotropic Hydrodynamics with a Realistic Scalar Scattering Kernel Dekrayat Almaalol, Micheal Strickland Prior studies of nonequilibrium dynamics using anisotropic hydrodynamics have all relied on the use of the relativistic AndersonWitting scattering kernel. In this paper, we make the first study of the impact of using a more realistic scalar scattering kernel in anisotropic hydrodynamics. For this purpose, we consider a conformal transversally homogenous system undergoing boostinvariant Bjorken expansion and take the collisional kernel to be given by the leading order $2 \leftrightarrow 2$ scattering kernel in scalar $\lambda \phi^4$. We consider both classical and quantum statistics in order to assess the impact of Bose enhancement on the dynamics. We also determine the anisotropic nonequilibrium attractor of a system subject to this collisional kernel in the context of anisotropic hydrodynamics. We find that, when the shear viscosity to entropy density ratio ($\eta/s$) obtained using the AndersonWitting and scalar collisional kernels is matched, the system develops a higher degree of earlytime momentumspace anisotropy given the same value of $\eta/s$. Additionally, we find that taking into account Bose enhancement further increases earlytime momentumspace anisotropy. [Preview Abstract] 
Monday, April 16, 2018 2:30PM  2:42PM 
S12.00004: Quark and Gluon Collective Modes with Momentum Anisotropy Babak Salehi Kasmaei, Michael Strickland The Selfenergies and dispersion relations of the quark and gluon collective excitations are modified by medium effects in a hot and momentum anisotropic quarkgluon plasma. This can affect various observables of the heavyion collision experiments and provide information about earlier stages of the quarkgluon plasma evolution. We calculate the hard loop selfenergies and dispersion relations of the collective excitations for both of the quark and gluon modes with various types and strengths of momentum anisotropy. We show the full direction dependence of the effective masses and unstable modes of the quark and gluon quasiparticles. [Preview Abstract] 
Monday, April 16, 2018 2:42PM  2:54PM 
S12.00005: Freestreaming as a preequilibrium model for use with (3+1)dimensional hydrodynamical evolution models Derek Everett, Ulrich Heinz A (3+1)dimensional freestreaming module has been developed that converts an initial energy momentum tensor for a system of massless partons with arbitrary initial energy density but zero collective flow at time zero into an evolved energy momentum tensor at any later time. By writing the evolved energy momentum tensor at that later time in hydrodynamic form one obtains nontrivial initial conditions, including initial collective flow profiles and dissipative flows, for subsequent hydrodynamic evolution. [Preview Abstract] 
Monday, April 16, 2018 2:54PM  3:06PM 
S12.00006: Measurement of charged particle mixed higher order flow harmonics and nonlinear response coefficients in PbPb collisions Shengquan Tuo Higherorder flow harmonics can be measured either with respect to the event plane of the same order, a lower order event plane, or a mixture of lower order planes. Studies of flow harmonics using the same order event plane have been used to extract the transport properties of the hot and dense medium produced in the collisions and to explore initial state effects. The mixed higherorder harmonics have been proposed to have sensitivity to initial conditions and shear viscosity over entropy density ratio of the medium during the hydrodynamic evolution and at freezeout. In this talk, the mixed higher order flow harmonics and nonlinear response coefficients of charged particles are measured as a function of $p_{T}$ and centrality in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV and 5.02 TeV with the CMS detector. The results are obtained using the scalarproduct method, and cover a $p_{T}$ range from 0.3 to 8.0 GeV/c, pseudorapidity $\eta<0.8$, and a centrality range of 0  60\%. It is observed that the nonlinear response coefficients of the odd harmonics are larger than the even harmonic ones for $p_{T}$ less than 3 GeV/c. The results are compared with hydrodynamic predictions with different shear viscosity to entropy density ratios and different initial conditions. [Preview Abstract] 
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