Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session H14: Challenges for The Hydrodynamic Description of RHIC Data from All Kinds of CorrelationsLive Mini-Symposium
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Sponsoring Units: DNP Chair: Derek Teaney, Stony Brook |
Sunday, April 18, 2021 10:45AM - 11:21AM Live |
H14.00001: Hydrodynamics and RHIC data: successes, failures, and what comes next Invited Speaker: Ron Belmont In the standard model of heavy ion physics, energetic collisions of relativistic nuclei both large and small create a quark-gluon plasma that evolves hydrodynamically. A wide body of experimental evidence in support of this pictures has been collected over the last two decades of RHIC operations, alongside earlier data from the AGS and SPS and more recent data from the LHC. As a paradigm, this view seems to have very strong foundations. However, upon careful scrutiny, a portion of the body of experimental results has either not yet been described by hydrodynamics or exists in tension with current calculations. In this talk, we will discuss both the successes and failures of hydrodynamics and consider the possibilities for what comes next. [Preview Abstract] |
Sunday, April 18, 2021 11:21AM - 11:33AM Live |
H14.00002: Exploring theoretical uncertainties in the hydrodynamic description of relativistic heavy-ion collisions Cheng Chiu, Chun Shen We explore theoretical uncertainties in the hydrodynamic description of relativistic heavy-ion collisions by examining the full non-linear causality conditions and quantifying the second-order transport coefficients' role. The causality conditions impose physical constraints on the maximum allowed values of inverse Reynold's numbers during the hydrodynamic evolution. For large Au+Au collisions, we find the variations of final observables are small with and without imposing the causality conditions, suggesting a robust extraction of the transport coefficients through model-to-data comparisons. However, sizable sensitivity is present in small p+Au collisions, which poses challenges to studying the small systems' collectivity. [Preview Abstract] |
Sunday, April 18, 2021 11:33AM - 11:45AM Live |
H14.00003: ~~Geometry and Dynamics in Heavy-ion Collisions Seen by the Femtoscopy Method in the STAR experiment Hanna Zbroszczyk ~~Geometry and dynamics of the particle-emitting source in heavy-ion collisions can be inferred via the femtoscopy method. Two-particle correlations at small relative momentum exploit Quantum Statistics (QS) and the Final State Interactions (FSI), which allow one to study the space-time characteristics of the source of the order of fm and 10 to the power of -23 s. The RHIC Beam Energy Scan (BES) program covers a significant part of the QCD Phase Diagram using Au nuclei collisions for several beam energies from 7.7 to 200 GeV, where the baryon-rich region is studied via femtoscopy. Baryon measurements, together with meson ones, provide complementary information about source characteristics. In this talk, results on femtoscopic measurements of various particle combinations for different collision energies and centralities will be shown. The results of non-identical particles enable studies of space-time asymmetries in the emission process. Besides, femtoscopy enables the investigation of FSI between hadrons. [Preview Abstract] |
Sunday, April 18, 2021 11:45AM - 11:57AM Live |
H14.00004: Exploring the quadrupole deformation in uranium nuclei at STAR Chunjian Zhang Collective phenomena in heavy-ion collisions are very sensitive to initial geometry including nuclei deformation effects. Recent hydrodynamic model calculations suggest that such deformation effects can be probed by studying event-by-event mean $p_T$ ($\left \langle p_T \right \rangle$) fluctuation and the correlation between the mean $p_T$ and harmonic flow ($v_n$). In particular, due to prolate shape of the uranium nuclei, significant difference between Au+Au and U+U collisions is expected for these observables. Results on the high-order cumulants of $\left \langle p_T \right \rangle$ fluctuations and Pearson correlation coefficient between $\left \langle p_T \right \rangle$ and $v_n$ as a function of centrality from Au+Au at $\sqrt{s_{NN}}$ = 200 GeV and U+U at $\sqrt{s_{NN}}$ = 193 GeV collisions with the STAR detector will be presented. Precise data-model comparison could be helpful to constrain the quadrupole deformation parameter $\beta_2$ of uranium nuclei. [Preview Abstract] |
Sunday, April 18, 2021 11:57AM - 12:09PM Live |
H14.00005: Probing early-time longitudinal dynamics with the $\Lambda$’s polarization in relativsitic heavy-ion collisions Sangwook Ryu, Vahidin Jupic, Chun Shen We systematically study the global $\Lambda$ polarization sensitivity to collision systems’ initial longitudinal flow velocity in hydrodynamic simulations. By explicitly imposing energy-momentum conservation when mapping the initial collision geometry to macroscopic hydrodynamic fields, we study the evolution of systems’ orbital angular momentum and fluid vorticity. The spin polarization of $\Lambda$ is compared with the STAR measurements in the Au+Au collisions from 7.7 GeV to 200 GeV. We further extend our model to make predictions for Pb+Pb collisions at 5020 GeV and Au+Au collisions at 3 GeV in the STAR fix target experiments at RHIC. [Preview Abstract] |
Sunday, April 18, 2021 12:09PM - 12:21PM Live |
H14.00006: Cumulant analysis of deformed systems using AMPT model Somadutta Bhatta The collective phenomena in heavy ion collisions are sensitive to initial nuclear geometry. Data from heavy Ion collisions of $^{197}$Au+$^{197}$Au and $^{238}$U+$^{238}$U at $\sqrt{s_{NN}}=200$ GeV from STAR experiment have been studied extensively in the recent past. Between these systems, Au is a spherical system whereas U has a prolate deformation. This deformation effect is expected to affect the magnitude of flow fluctuations. A measurement of flow cumulants in these systems using models like AMPT will help us constrain the initial geometry and medium properties. An AMPT study of flow cumulants can also help resolve the disagreement between the different estimates of the deformation parameter $\beta_{2}$ of isobaric systems $_{44}^{96}$Ru and $_{40}^{96}$Zr. This talk will present a study on the effect of deformation on flow cumulants using AMPT simulation. Symmetric and asymmetric cumulants for both systems with varying deformation parameters will also be compared and discussed. [Preview Abstract] |
Sunday, April 18, 2021 12:21PM - 12:33PM Live |
H14.00007: Non-Trivial Initial State Anisotropies and their effects on observables Nicolas Fortier Initial state geometry is a key component of descriptions of observables in heavy ion collisions. It is usually entirely determined by the properties of the collision. That is, two spherically symmetric nuclei, such as Au or Pb, can only produce specific subtypes of anisotropies that are resolved by how much overlap between the two nuclei is generated by a specific event, modulo small fluctuations in nucleon configurations. These anisotropies and their primary effects have been studied at length both theoretically and experimentally. However, the study of spherically symmetric nuclei via heavy ion collisions alone cannot fully distinguish between the effects of collision centrality and initial state geometry on the intermediate (Quark-Gluon Plasma (QGP)) and final states. By using deformed collision systems, such as U$^{238}$, one can create non-trivial initial state anisotropies that help separate their effects from pure consequences of centrality. In this talk, we will show that the QCD-based initial state model IP-Glasma, coupled to relativistic hydrodynamics and hadronic cascade programs, is capable of reproducing STAR data for U+U at $\sqrt{s_{NN}} = 193$ GeV while providing key insights into how these anisotropies affect both QGP flow and observables. [Preview Abstract] |
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