Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session LC: Heavy Ions and Thermal Fluctuations |
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Chair: Kevin Dusling, Phys Rev Letters |
Saturday, October 31, 2020 10:30AM - 10:42AM |
LC.00001: Fluctuations and Self-Correlations in Relativistic Heavy-Ion Collisions. Aritra De, Christopher Plumberg, Joseph Kapusta Hydrodynamic modelling explains the behavior of quark gluon plasma in heavy ion collisions very well. Fluctuations in such hydrodynamic equations lets us study the various thermal and transport properties of the medium. Since critical points are characterized by large fluctuations, the hope is that this line of investigation will help us identify the presence of a critical point in the QCD phase diagram. In this talk I will describe the study of fluctuations in electric charge in heavy ion collisions using a causal noise called Catteneo noise. We will discuss how a lattice of noise fluctuations is required to fully calculate the two-point correlators of charge. A numerical procedure will be introduced to solve the stochastic differential equations that arise from the charge conservation equation on the lattice event-by-event. I will also identify the `self-correlation' term in the case of Catteneo noise and provide a physical interpretation. In conclusion, I will also compare the hydrokinetic approach with our framework. [Preview Abstract] |
Saturday, October 31, 2020 10:42AM - 10:54AM |
LC.00002: Higher-Order Cumulants of Net-Proton Multiplicity Distributions in Au+Au $\sqrt{s_{NN}}$ = 3 GeV at STAR Samuel Heppelmann The first RHIC Beam Energy Scan (BES-I), $\sqrt{s_{NN}}$ = 7.7 GeV to $\sqrt{s_{NN}}$ = 200 GeV, was run from 2010-2014 to search for the turn-off signatures of the quark-gluon plasma (QGP). The QGP signatures studied in BES-I became insensitive at energies below $\sqrt{s_{NN}}$ = 19.6 GeV. The fluctuations in the event-by-event net-proton multiplicities exhibited a dip in the kurtosis $ \times $ variance of the net-proton number at $\sqrt{s_{NN}}$ = 19.6 GeV and a rise at 7.7 GeV. Motivated by the findings of BES-I, STAR has initiated a phase II of the BES program (BES-II) and the Fixed Target program. The BES-II program improves upon the earlier BES-I program with increased detector acceptance, luminosity, and statistics at each energy, while the Fixed Target Program extends the minimum energy. In this talk, results from the 2018 first dedicated fixed target physics run at $\sqrt{s_{NN}} = 3$ GeV will be presented. We will discuss the cumulants of event-by-event net-proton multiplicities as a function of rapidity and centrality. The results will be compared to results from the BES-I program and the HADES experiment. [Preview Abstract] |
Saturday, October 31, 2020 10:54AM - 11:06AM |
LC.00003: Hadronic resonances and the chemical-freeze out in heavy-ion collisions Jamie Stafford, Paolo Alba, Valentina Mantovani-Sarti, Jacquelyn Noronha-Hostler, Paolo Parotto, Israel Portillo, Claudia Ratti The influence of hadronic resonances on the chemical freeze-out in heavy-ion collisions is investigated in this study [1]. Detailed knowledge of the hadronic spectrum is still an open question, which has phenomenological consequences on the study of heavy-ion collisions. In this work, we determine the effect of varying the number of particles in the system on thermal fit parameters. We make use of several different hadron lists, including those that consider experimentally observed and theoretically predicted states, in order to provide a complete picture. The freeze-out parameters are extracted from thermal fits of particle yields and net-particle fluctuations, both calculated within the Hadron Resonance Gas model. We find that additional resonances tend to decrease the freeze-out temperature while exhibiting a mild effect on the baryonic chemical potential. We also note that the inclusion of heavier resonances is not sufficient to eliminate the gap between the light and strangeness freeze-out conditions. [1] P. Alba \textit{et al}. Phys.Rev.C 101 (2020) 5, 054905~ [Preview Abstract] |
Saturday, October 31, 2020 11:06AM - 11:18AM |
LC.00004: Centrality and Flavor Dependence of the Chemical Freeze-out of Light Nuclei in Heavy Ion Collisions via Statistical Hadronization Fernando Antonio Flor, Gabrielle Olinger, Rene Bellwied Statistical Hadronization Models (SHMs) have successfully reproduced hadronic particle abundances over nine orders of magnitude in high energy collisions of heavy ions. Experimental particle yields at RHIC and the LHC serve as the cornerstone for extracting common freeze-out parameters in the QCD phase diagram -- namely, the baryo-chemical potential ($\mu_B$) and the chemical freeze-out temperature ($T_{ch}$) -- via thermal fits in the SHM framework. The differences between the extracted $T_{ch}$ values of light hadrons and the strange hadrons becomes a point of interest when including light nuclei and hypernuclei in the PDG2016+ hadronic spectrum. In this talk, I will present calculations of the freeze-out parameters from hadronic yields from STAR and ALICE via the Grand Canonical approach within the framework of the Thermal FIST package. I will show that nuclei and hypernuclei yields can both be excellently described within the SHM framework. Lastly, I will show that the inclusion of light nuclei and hypernuclei in the light and strange fits, respectively, are consistent with our previously shown $T_{ch}$ values -- differing by more than 10 MeV; providing evidence for a flavor-dependent freeze-out in the QCD crossover region. [Preview Abstract] |
Saturday, October 31, 2020 11:18AM - 11:30AM |
LC.00005: System size dependence of the hadronization temperature for light and strange baryons in relativistic particle collisions at ALICE Gabrielle Olinger, Fernando Flor, René Bellwied Statistical Hadronization Models (SHMs) have been shown to adequately reproduce hadronic particle abundances produced in high energy collisions of heavy ions at ALICE. Identified particle yields are used in determining freeze-out parameters of the QCD phase diagram via thermal fits in the SHM framework. When comparing fit results to varying sets of particles, differences in the chemical freeze-out temperature ($T_{ch}$) arise between light and strange hadrons. In this talk, I will show the system size and flavor dependence of $T_{ch}$ via fits to experimental yields for several centrality classes in PbPb, pPb, and pp collisions measured by ALICE. I will compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions. Additionally, I will examine how the normalized hadron to pion yield ratios of light and strange baryons, as well as the $\phi$ meson, evolve within a flavor dependent model. Through a unique two-temperature approach, I will show that flavor dependence of the freeze-out parameters leads to a natural explanation of strangeness enhancement from small to large systems. [Preview Abstract] |
Saturday, October 31, 2020 11:30AM - 11:42AM |
LC.00006: Bulk Viscosity and Cavitation in Heavy Ion Collisions Megan Byres, Sanghoon Lim, Chris McGinn, Jeff Ouellette, James Nagle Relativistic heavy ion collisions generate nuclear-sized droplets of quark-gluon plasma (QGP) that exhibit nearly inviscid hydrodynamic expansion. Smaller collision systems such as p+Au, d+Au, and $^{3}$He+Au at the Relativistic Heavy Ion Collider, as well as p+Pb and high-multiplicity p+p at the Large Hadron Collider may create even smaller droplets of QGP. If so, the standard time evolution paradigm of heavy ion collisions may be extended to these smaller systems. These small systems present a unique opportunity to examine pre-hydrodynamic physics and extract properties of the QGP, such as the bulk viscosity, where the short lifetimes of the small droplets makes them more sensitive to these contributions. Here we focus on the influence of bulk viscosity, its temperature dependence, and the implications of negative pressure and potential cavitation effects on the dynamics in small and large systems using the publicly available hydrodynamic codes SONIC and MUSIC. We also discuss pre-hydrodynamic physics in different frameworks including AdS/CFT strong coupling, IP-GLASMA weak coupling, and free streaming. [Preview Abstract] |
Saturday, October 31, 2020 11:42AM - 11:54AM |
LC.00007: The thermodynamics of large-N QCD and the nature of metastable phases Yukari Yamauchi, Thomas Cohen, Scott Lawrence In the limit of a large number of colors ($N$), both Yang-Mills and quantum chromodynamics are expected to have a first-order phase transition separating a confined hadronic phase and a deconfined plasma phase. The existence of a first-order transition suggests that the hadronic phase can be superheated and the plasma phase supercooled. The talk will focus on the thermodynamic nature of such metastable phases and beyond their endpoints. The supercooled deconfined plasma at large $N$, if it exists, has negative absolute pressure -- a pressure below that of the vacuum. For energy densities beyond the endpoint of the hadronic superheated phase, a description of homogeneous matter composed of ordinary hadrons with masses of order unity in a $1/N$ expansion can exist, and acts as though it has the constant Hagedorn temperature in the $N \rightarrow \infty$ limit. In this regime, the connection between the canonical and microcanonical descriptions breaks down and the system cannot fully equilibrate as $N \rightarrow \infty$. Rather, in a hadronic description, energy is pushed to hadrons with arbitrarily large masses. [Preview Abstract] |
Saturday, October 31, 2020 11:54AM - 12:06PM |
LC.00008: High-Energy Phase Diagrams with Charge and Isospin Axes under Heavy-Ion Collision and Stellar Conditions Krishna Aryal, Veronica Dexheimer We investigate the phase transition from hadron to quark matter in the general case without the assumption of chemical equilibrium with respect to weak decays. The effects of net strangeness on charge and isospin fractions, chemical potentials, and temperature are studied in the context of the Chiral Mean Field (CMF) model that incorporates chiral symmetry restoration and deconfinement. The extent to which these quantities are probed during deconfinement conditions expected to exist in protoneutron stars, binary neutron-star mergers, and heavy-ion collisions is analyzed quantitatively via the construction of 3-dimensional phase diagrams. [Preview Abstract] |
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