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 MJ: Mini-Symposium: Search for the Critical Point III |
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Chair: Derek Teaney, Stony Brook University Room: Salon C |
Wednesday, October 16, 2019 2:00PM - 2:36PM |
MJ.00001: Search for the QCD Critical Point at RHIC Invited Speaker: Roli Esha At large baryon chemical potentials, QCD-based models predict the phase transition from the Quark Gluon Plasma phase to the Hadron Gas phase to be a first-order phase transition that ends in a second-order critical point. The Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC) focusses on the searches for a possible critical point in the quark-hadron phase diagram. The experimental searches rely on studies of fluctuations of conserved quantum numbers, namely the baryon, strangeness or charge fluctuations. In this talk, the results and implications from such experimental measurements at RHIC will be reviewed. Future plans for the BES-II program will also be discussed. [Preview Abstract] |
Wednesday, October 16, 2019 2:36PM - 2:48PM |
MJ.00002: Search for the QCD critical end point with finite-size succeptibility scaling functions Roy Lacey Finite-size and Finite-time effects complicate the search for the critical endpoint (CEP) as well as its characterization because they impose non-trivial constraints on the growth of the correlation length. Thus, the observation of non-monotonic experimental signatures for the CEP is not sufficient to identify its location and assign its universality class. In this talk, I will discuss how susceptibility scaling functions can be leveraged to locate and characterize the CEP. To date, this constitutes the only credible experimental approach to discovering and characterizing the CEP. [Preview Abstract] |
Wednesday, October 16, 2019 2:48PM - 3:00PM |
MJ.00003: Fluctuation dynamics near the QCD critical point Lipei Du, Ulrich Heinz, Krishna Rajagopal, Yi Yin Near the QCD critical point (CP), critically slow processes can invalidate the conventional (dissipative) hydrodynamic description, which simply integrates out all non-hydrodynamic modes. We explore the critical dynamics near the QCD CP with the novel Hydro+ framework which extends the conventional hydrodynamic description by coupling it to additional explicitly evolving slow modes. Their slow relaxation is controlled by the correlation length in the critical region, which is independent from the density inhomogeneities of the QCD matter that control the evolution of the hydrodynamic quantities. In this presentation we study the evolution of a single critical slow mode on top of a simplified matter background with non-zero net baryon density undergoing Gubser flow, as a function of its wave number and the correlation length. We also discuss how the non-equilibrium slow mode affects the bulk properties of the matter, such as the pressure and entropy density. We find that over a wide range of wave numbers the non-equilibrium effects are dominated by the fluid expansion rather than by critical slowing-down. Last but not least we explore the critical fluctuation dynamics in systems of various sizes and at different collision energies. [Preview Abstract] |
Wednesday, October 16, 2019 3:00PM - 3:12PM |
MJ.00004: Relativistic Dynamics of Fluctuations Away and Near the QCD Critical Point Xin An, Gokce Basar, Mikhail Stephanov, Ho-Ung Yee To describe dynamics of bulk and fluctuations near the QCD critical point we develop general relativistic fluctuation formalism for a fluid carrying baryon charge. Feedback of fluctuations modifies hydrodynamic coefficients including bulk viscosity and conductivity. We perform necessary UV renormalization to obtain cutoff independent deterministic equations suitable for numerical implementation. Focusing on the critical mode we show how this general formalism matches existing Hydro+ description of fluctuations near the QCD critical point and nontrivially extends it inside and outside of the critical region. [Preview Abstract] |
Wednesday, October 16, 2019 3:12PM - 3:24PM |
MJ.00005: Bulk and shear thermal fluctuations in heavy-ion collisions Mayank Singh, Chun Shen, Sangyong Jeon, Charles Gale Hydrodynamical simulations of heavy-ion collisions largely ignore the thermal fluctuations demanded by the fluctuation-dissipation theorem. In this talk we present our full calculations showing the effect of fluctuations corresponding to both shear and bulk dissipation on the heavy-ion collision simulations, for the first time. Stochastic terms corresponding to thermal fluctuations are introduced in the state of the art (3+1) D viscous hydrodynamics package MUSIC. By the technique of noise filtering - selectively removing high wavenumber modes above a cutoff ($\lambda_{\text{cut}}$) - we are able to consistently introduce thermal noise as source terms for hydrodynamics fields [1]. We use IP-Glasma initial states and UrQMD hadronic cascade along with MUSIC to realize a comprehensive modeling. Our calculations quantify the impact of thermal fluctuations on two-point correlation in both short and long range. We compare our approach with the complementary hydro-kinetic method of studying hydrodynamic fluctuations in a Bjorken background flow. Renormalization group flow of transport coefficients as a function of $\lambda_{\text{cut}}$ will also be discussed. [1] Singh, M., Shen, C., McDonald, S., Jeon, S. and Gale, C., Nucl. Phys. A 982, 319-322 (2019) [Preview Abstract] |
Wednesday, October 16, 2019 3:24PM - 3:36PM |
MJ.00006: Evolution of critical fluctuations in Bjorken expansion and its effects on two-particle rapidity correlations Chandrodoy Chattopadhyay, Lipei Du, Ulrich Heinz A novel way of locating the QCD critical point is to look for correlations in certain final state observables of heavy ion collisions which may be potential signatures of long-range correlations and large fluctuations taking place in the hot and dense systems as they transit the critical domain. In this work, we study two-particle rapidity correlations induced from fluctuations of hydrodynamic variables in a system undergoing Bjorken expansion which passes close to the QCD critical point. The dynamics of fluctuations are described by deterministic hydro-kinetic equations for out-of-equilibrium two-point functions, and the effects of critical behaviour of transport coefficients and correlation length, and of the medium expansion are systematically investigated. Differences of our findings from those obtained using a straightforward extrapolation of the traditional theory of hydrodynamic fluctuations to the critical regime are discussed. Comparisons with results for two-particle correlations stemming from fluctuations away from the critical point are presented to distinguish the effects of criticality. [Preview Abstract] |
Wednesday, October 16, 2019 3:36PM - 3:48PM |
MJ.00007: Proton Yields, Multiplicities, and Event-by-event Fluctuations for Au + Au at $\sqrt{s_{NN}}$ from 3 GeV samuel heppelmann The first RHIC Beam Energy Scan (BES-I) was run from 2010-2014 to search for the turn-off of signatures of the quark-gluon plasma (QGP), evidence of the first-order phase transition, and the possible QCD critical point. Motivated by the findings of BES-I, STAR has initiated a phase II of the BES program (BES-II). The BES-II program improves upon the earlier BES-I program with detector upgrades to extend the acceptance, higher luminosity to provide 10-20 times better statistics at each energy, and a Fixed-Target program to extend the range of BES-II below the expected critical point. In this talk, results from the first dedicated fixed-target physics run at $\sqrt{s_{NN}} = 3$ GeV will be presented. We present proton (and antiproton) yields and multiplicities. These measurements will be compared with results from AGS experiments E866 and E895. We will discuss the implications of the observed multiplicities and efficiency corrections to the study of cumulants of event-by-event net-proton multiplicities up to the fourth order as a function of rapidity. Results at this energy will help to understand the trends observed in the previous results from the BES program and preliminary results from HADES. We will discuss the future of BES-II fixed-target measurements at RHIC. [Preview Abstract] |
Wednesday, October 16, 2019 3:48PM - 4:00PM |
MJ.00008: Initial Conditions from Gluon Multiplicity in Heavy Ion Collisions Patrick Carzon, Jacquelyn Noronha-Hostler, Matthew Sievert A great uncertainty in heavy-ion collisions is the initial state immediately after the collision. A question remains regarding the optimal method of determining the energy density deposited at mid-rapidity by a collision. This is important because the viscosity of the quark-gluon plasma is very small, and the final-state flow will be sensitive to this choice in the initial state. TRENTO accomplishes this in a phenomenological way by taking $\sqrt{T_A T_B}$ to provide a reduced thickness function, that when scaled by a data-determined factor provides an entropy density. Another way of calculating the initial energy density is using a proportionality to $T_A T_B$, which comes from Color-Glass Condensate calculations at $\tau = 0$. I will present a new method of calculating the reduced thickness using the single-inclusive gluon cross section in the dilute-dense limit of the CGC framework. There is a noticeable difference, across system size, between observables in the standard setting of TRENTO and this new method. We also study quantitatively various approximations which are commonly made in such calculations. The gluon distribution employed here provides a platform on which to later introduce new conserved charges into hydrodynamics when supplemented by quark splitting functions. [Preview Abstract] |
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