Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session KJ: Mini-symposium: Search for the Critical Point I |
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Chair: Jacquelyn Noronha-Hostler, Rutgers University Room: Salon C |
Wednesday, October 16, 2019 8:30AM - 9:06AM |
KJ.00001: QCD phase diagram from lattice Invited Speaker: Peter Petreczky I will discuss recent lattice results on the QCD phase diagram at non-zero temperature and density using Taylor expansion. I will present results on the chiral and deconfinement aspects of the QCD transition as function of the light quark mass. I will clarify the relation of the phase transition at zero quark mass to the crossover and critical point at small densities and physical pion masses. [Preview Abstract] |
Wednesday, October 16, 2019 9:06AM - 9:18AM |
KJ.00002: Phase transitions and transport in dense nuclear matter from relativistic density functional theory Agnieszka Wergieluk, Volker Koch The equation of state of dense nuclear matter, while central in simulations of QCD systems under extreme conditions, is currently inaccessible to first principles calculations. Using relativistic density functional theory, we model the thermodynamics and single-particle equations of motion of nuclear matter over a broad range of temperatures and densities encompassing nuclei, neutron stars, neutron star mergers, and relativistic heavy ion collisions. We obtain a flexible and thermodynamically consistent framework to parameterize the known properties of ordinary nuclear matter and postulate a family of equations of state compatible with the QCD phase transition. Eventually, these equations of state will be constrained by comparison with experimental data. As a first step, we implement the corresponding relativistically covariant single-particle equations of motion within a hadronic transport model and investigate the behavior of dense nuclear matter close to the phase transition. [Preview Abstract] |
Wednesday, October 16, 2019 9:18AM - 9:30AM |
KJ.00003: Using Characteristic Temperatures of Transport Coefficients to Search for the QCD Critical Point Travis Dore, Jacquelyn Noronha-Hostler, Matt Sievert While at at zero baryon chemical potentials one expects a minimum in the shear viscosity over entropy density and a maximum in the bulk viscosity to entropy density ratio, the exact values where these characteristic temperatures occur has not yet been determined from first principle Lattice QCD calculations and may occur anywhere within the cross-over regime of the phase transition. However, if there is a critical point in the QCD phase diagram then all characteristic temperatures should converge and, depending on the universality class, some of the hydrodynamic transport coefficients themselves may diverge. In order to explore out-of-equilibrium effects in the QCD phase diagram we use 1+0D (Bjorken flow) viscous hydrodynamics to study the hydrodynamical lifetime, cavitation, and attractor physics in a simple cross-over phase transition versus one with a critical point (where we expect all characteristic temperatures to converge). Comparisons between results obtained using an equation of state with nonzero baryon, strange, and electric charge chemical potentials and results obtained using the assumption of only a finite baryon chemical potential (i.e. $\mu_S=\mu_Q=0$) are also made. [Preview Abstract] |
Wednesday, October 16, 2019 9:30AM - 9:42AM |
KJ.00004: Transits of the QCD Critical Point Derek Teaney, Fanglida Yan, Yi Yin, Yukinao Akamatsu We analyze the evolution of hydrodynamic fluctuations in a heavy ion collision as the system passes close to the QCD critical point. We introduce two small dimensionless parameters $\lambda$ and $\Delta_s$ to characterize the evolution. $\lambda$ compares the microscopic relaxation time (away from the critical point) to the expansion rate $\lambda \equiv \tau_0/\tau_Q$, and $\Delta_s$ compares the baryon to entropy ratio, $n/s$, to its critical value, $\Delta_s\equiv (n/s - n_c/s_c)/(n_c/s_c)$. We determine how the evolution of critical hydrodynamic fluctuations depends parametrically on $\lambda$ and $\Delta_s$. Finally, we use this parametric reasoning to estimate the critical fluctuations and correlation length for a heavy ion collision, and to give guidance to the experimental search for the QCD critical point. [Preview Abstract] |
Wednesday, October 16, 2019 9:42AM - 9:54AM |
KJ.00005: System size and flavor dependence of chemical freeze-out in relativistic particle collisions from RHIC-BES to LHC energies Gabrielle Olinger, Rene Bellwied, Fernando Flor The Statistical Hadronization Model (SHM) has been tested to adequately reproduce hadronic particle abundances over nine orders of magnitude in high energy collisions of heavy ions. Experimental particle yields at RHIC and the LHC are used in determining freeze-out parameters of the QCD phase diagram via thermal fits in the SHM framework. When comparing extracted freeze-out parameters obtained using different sets of particles in the thermal fit, differences in the chemical freeze-out temperature arise between light and strange hadrons. In this talk, I will show recent calculations of freeze-out parameters using particle yields from STAR and ALICE collisions at $\sqrt{s_{NN}}=$ 7.7 GeV - 7.0 TeV. Using the Grand Canonical approach within the Thermal FIST HRG model, I will show evidence for a flavor-dependent freeze-out in the QCD crossover region and compare to lattice calculations. Lastly, I will compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions. With the same approach applied to pp and pPb collisions, I will show that the SHM is applicable to small systems and that flavor dependencies in the freeze-out parameters lead to a natural explanation of strangeness enhancement from small to large systems. [Preview Abstract] |
Wednesday, October 16, 2019 9:54AM - 10:06AM |
KJ.00006: Yields of weakly-bound light nuclei as a probe of the statistical hadronization model Yukari Yamauchi, Yiming Cai, Thomas Cohen, Boris Gelman The statistical hadronization model is a simple and efficient phenomenological framework in which the relative yields for very high energy heavy ion collisions are essentially determined by the chemical freeze-out temperature. Recent measurements of yields of hadrons and light nuclei from the ALICE collaboration at the LHC were described by the model with remarkable accuracy with a chemical freeze-out temperature of 156.5 $\pm$ 1.5 MeV. A key physical question is whether the freeze-out temperature can be understood as the temperature at which the various species of an equilibrated gas of hadrons (including resonances) and nuclei chemically freeze out as the model assumes, or whether it successfully parametrizes the yield data for a different reason. The analysis of the yields of weakly-bound light nuclei indicates that a key assumption underlying the model---that hadrons (and nuclei), just prior to chemical freeze-out temperature, are in thermal equilibrium and are sufficiently dilute as to have particle distributions accurately described statistically by a nearly ideal gas of hadrons and nuclei with masses given by their free space values --- appears to be inconsistent with the chemical freeze-out temperature output by the model, at least for these weakly-bound light nuclei. [Preview Abstract] |
Wednesday, October 16, 2019 10:06AM - 10:18AM |
KJ.00007: Charged Particle Distributions in Central Au+Au Collisions at $\sqrt{s_{NN}}=3.0$ GeV at STAR Benjamin Kimelman The RHIC Beam Energy Scan phase I (BES-I) program provided a detailed study of nuclear matter over a wide range of energies. Below $\sqrt{s_{NN}}<19.6$ GeV, interesting results were shown in hadron azimuthal anisotropies, particle ratios, and net-proton higher moments. These results motivate the Beam Energy Scan phase II (BES-II). Compared to BES-I, BES-II will have improvements including increased statistics by a factor of 10 to 20 for each energy, improved acceptance from upgrades to the STAR experiment, and an extension of the energy reach from $\sqrt{s_{NN}}=7.7$ GeV to $\sqrt{s_{NN}}=3.0$ GeV with the STAR fixed-target program. This talk will present results from the lowest fixed target energy to be studied in BES-II including transverse mass spectra, rapidity density distributions, particle ratios, and centrality dependence for charged hadrons. These results are analyzed with a chemical equilibrium model to determine the chemical temperature and potential at freeze-out. The pion ratio and Coulomb potential will also be presented. At low energy, produced particles are sensitive to a Coulomb potential from a net positive source at low momenta which modifies the transverse mass spectra. These new data are compared to previously published results from experiments at the AGS. [Preview Abstract] |
Wednesday, October 16, 2019 10:18AM - 10:30AM |
KJ.00008: Charged Particle Spectra from Au+Au $\sqrt{s_{NN}}=27$ GeV Collisions at STAR Matthew Harasty The RHIC beam energy scan I (BES-I) ran from 2010 to 2014 and covered a range of energies from $\sqrt{ s_{NN} } $ = 62.4 to 7.7 GeV. Midrapidity spectra for $\pi$, $K$, and p have been published from those data. Those and other results have justified a new beam energy scan (BES-II) with high statistics and a series of detector upgrades. The first collider energy from BES-II, 27 GeV, was run in 2018. For this run a single sector of the inner time projection chamber (iTPC) upgrade was available. This detector upgrade extended the coverage of the STAR detector to lower $p_T$ and higher $\eta$. This talk will report the spectra and yields of $\pi$, $K$, and p as a function of rapidity and centrality from the 27 GeV Au+Au collisions from 2018 at the Relativistic Heavy Ion Collider. The relative yields of the various particle species allows one to measure the chemical freeze-out temperature and baryon chemical potential. The extended coverage provided by the iTPC upgrade will improve estimates of the full 4$\pi$ yields. The parameters extracted from the 4$\pi$ yields in the current analysis are compared to previous experimental results extracted from midrapidity particle yields to address the evolution of the baryon chemical potential as a function of rapidity. [Preview Abstract] |
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