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 EC: Flow I |
Hide Abstracts |
Chair: Roy Lacey, Stony Brook |
Friday, October 30, 2020 10:30AM - 10:42AM |
EC.00001: Inferring properties of Quark Gluon Plasma Derek Everett We present state-of-the-art quantifications of transport properties of quark-gluon plasma using hadronic observables from both the Relativistic Heavy Ion Collider and the Large Hadron Collider, simulated with the JETSCAPE framework. We focus on the first-order transport coefficients of the Quantum Chromodynamic plasma, the specific shear and bulk viscosities. Important sources of theoretical uncertainty are quantified and accounted for in final estimates of the viscosities. These include the uncertainty in modelling the first fm/c of the collisions, as well as the theoretical ambiguity in mapping hydrodynamic fields to non-equilibrium hadronic spectra. Additionally, some uncertainty stemming from second-order transport coefficients is discussed. Finally, the hydrodynamic hybrid model is compared to model variations, strengthening its support. [Preview Abstract] |
Friday, October 30, 2020 10:42AM - 10:54AM |
EC.00002: Interferometric Signatures of Collectivity in Small Systems Christopher Plumberg Particle interferometry has proven to be an indispensable tool in probing the space-time evolution of femtoscopic collision systems. In this talk, I show how hydrodynamic predictions for the space-time evolution of high-multiplicity p$+$p and p$+$Pb collisions can be tested against interferometric observables designed to probe their size and shape. In particular, I consider how the dependence of these observables on the multiplicity $dN_{ch}/d\eta $ may reflect the hydrodynamic nature of the evolving system. [Preview Abstract] |
Friday, October 30, 2020 10:54AM - 11:06AM |
EC.00003: Flow Cumulants for Multi Particle Azimuthal Correlations in Heavy-Ion Collisions Somadutta Bhatta Cumulant expansion of multiparticle azimuthal correlations is one of the most effective methods to measure the transverse momentum azimuthal anisotropy without the errors arising from non-uniform detector acceptance. These correlations are sensitive to the initial fluctuations and transport properties of the medium created in heavy ion collisions. In one of the first ATLAS measurements of azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV using a dataset of approximately 7 $\mu$b$^{-1}$, the Fourier coefficients were evaluated using multi-particle cumulants calculated with the generating function method. This work shows that the $v_{n}$ measured with four-particle cumulants are significantly reduced compared to the measurement involving two-particle cumulants and that the models of the initial spatial geometry and its fluctuations fail to describe the flow fluctuations measurements. In another ATLAS measurement using using 470 $\mu$b$^{-1}$ of Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV provided new information to disentangle flow fluctuations from the initial and final states, as well as gave new insights on the influence of centrality fluctuations. Sign change of multi-particle mixed-harmonics was emphasized in this work. [Preview Abstract] |
Friday, October 30, 2020 11:06AM - 11:18AM |
EC.00004: Explore the nuclei deformation with mean transverse momentum and anisotropy flow in heavy-ion collisions Chunjian Zhang, Shengli Huang 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 mean $p_T$ and harmonic flow. In particular, due to prolate shape of the Uranium nuclei, significant difference between Au+Au and U+U collisions is expected for these observables. This talk presents new measurements 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. 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 harmonic flow $v_n$ from these two systems will be presented. The results will be compared with model calculations to constrain initial geometry as well as medium properties and final state effects in these collisions. [Preview Abstract] |
Friday, October 30, 2020 11:18AM - 11:30AM |
EC.00005: Flow and transverse momentum correlations in Pb+Pb and Xe+Xe collisions with ATLAS Arabinda Behera Correlation of mean transverse momentum ($[p_T]$) of particles with the n-th order anisotropic flow harmonics ($v_n$) in heavy ion collisions is sensitive to the initial-state conditions. Measurement of a modified Pearson’s Correlation Coefficient between $v_n$ and $[p_T]$ with the ATLAS detector are presented using 22~${\mathalpha{\mu}}\textrm{b}^{-1}$ of $\sqrt{s_{\mathrm{NN}}}=5.02$~$\TeV$ TeV Pb+Pb collisions for harmonics n=2, 3 and 4. The results are shown as a function of event centrality quantified as the number of charged particles ($N_{ch}$) or the number of nucleon participants. The correlation coefficient depends strongly on centrality and also on the choice of transverse momentum range of the particles for all harmonics. Similar ATLAS analysis is in process for 3~${\mathalpha{\mu}}\textrm{b}^{-1}$ of $\sqrt{s_{\mathrm{NN}}}=5.44$~$\TeV$ Xe+Xe collisions. Comparison between Pb+Pb and Xe+Xe collisions can shed light on the system-size dependence of this correlation and the impact of deformation. The measurement will provide inputs for better understanding of the dynamics of heavy ion collisions and can help constrain theoretical models. [Preview Abstract] |
Friday, October 30, 2020 11:30AM - 11:42AM |
EC.00006: How to observe initial state momentum anisotropies in nuclear collisions Bjoern Schenke, Giuliano Giacalone, Chun Shen We show that the correlation between the elliptic momentum anisotropy, $v_2$, and average transverse momentum, $[p_T]$, in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+Music+UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the Color Glass Condensate, predicts a characteristic sign change of the correlator $\rho(v_2^2,[p_T])$ as a function of charged particle multiplicity in p+Au and d+Au collisions at $\sqrt{s}=200\,{\rm GeV}$, as well as p+Pb collisions at $\sqrt{s}=5020\,{\rm GeV}$. This sign change is absent in calculations without initial state momentum anisotropies. The model also predicts a clear difference between the centrality dependence of $\rho(v_2^2,[p_T])$ in Au+Au collisions at $\sqrt{s}=200\,{\rm GeV}$ and Pb+Pb collisions at $\sqrt{s}=5020\,{\rm GeV}$, with only the latter showing a sign change in peripheral events. Experimental observation of these distinct qualitative features of $\rho(v_2^2,[p_T])$ in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the Color Glass Condensate. [Preview Abstract] |
Friday, October 30, 2020 11:42AM - 11:54AM |
EC.00007: Hydrodynamic generator in RTA kinetic theory Mike McNelis, Ulrich Heinz We resum the non-equilibrium gradient corrections to a single-particle distribution function evolved by the Boltzmann equation in the relaxation time approximation (RTA). We first study a system undergoing Bjorken expansion and show that (for a constant relaxation time) the exact solution of the RTA Boltzmann equation at late times generates the Borel resummed Chapman-Enskog series. Extending this correspondence to systems without Bjorken symmetry, we construct a (3+1)-dimensional hydrodynamic generator for RTA kinetic theory, which is an integral representation of the Chapman-Enskog series in the limit of vanishing non-hydrodynamic modes. Relaxing this limit we find at earlier times a set of non-hydrodynamic modes coupled to the Chapman-Enskog expansion. Including the dynamics of these non-hydrodynamic modes is shown to control the emergence of hydrodynamics as an effective field theory description of non-equilibrium fluids, which works well even for far-off-equilibrium situations where the Knudsen number is initially large. [Preview Abstract] |
Friday, October 30, 2020 11:54AM - 12:06PM |
EC.00008: Non-equilibrium attractor in high-temperature QCD plasmas Dekrayat Almaalol, Michael Strickland, Aleksi Kurkela We establish the existence of a far-from-equilibrium attractor in weakly-coupled gauge theory undergoing one-dimensional Bjorken expansion. We demonstrate that the resulting far-from-equilibrium evolution is insensitive to certain features of the initial condition, including both the initial momentum-space anisotropy and initial occupancy. We find that this insensitivity extends beyond the energy-momentum tensor to the detailed form of the one-particle distribution function. Based on our results, we assess different procedures for reconstructing the full one-particle distribution function from the energy-momentum tensor along the attractor and discuss implications for the freeze-out procedure used in the phenomenological analysis of ultra-relativistic nuclear collisions. [Preview Abstract] |
Friday, October 30, 2020 12:06PM - 12:18PM |
EC.00009: Hydrodynamics from free-streaming to thermalization and back again Chandrodoy Chattopadhyay, Ulrich Heinz We explore the interplay of thermalizing and decoupling dynamics in (0$+$1)-dimensional expanding fluids with Bjorken symmetry by parametrically modifying the relaxation-time dependence of the Knudsen number, which controls the deviation of the system from local equilibrium. The corresponding response of the system characterized by its Reynolds number is shown to depict near-universal behavior whose trajectory as a function of the Knudsen number makes a characteristic turn as the system transits from a thermalizing to a decoupling regime. We argue that this feature is robust and should manifest itself in realistic 3-dimensional simulations of heavy-ion collision fireballs. [Preview Abstract] |
Friday, October 30, 2020 12:18PM - 12:30PM |
EC.00010: Kinetic and Chemical Equilibration of Quark-Gluon Plasma Xiaojian Du, Soeren Schlichting We establish a non-equilibrium QCD evolution model with light quark and gluon degrees of freedom. By including both elastic and inelastic scattering for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of quark-gluon plasma, and thus connect the initial (semi-) hard production of partons at early times with the hydrodynamic description of a near-thermalized quark-gluon plasma after the first fm/c of collision. Within this approach, we investigate the time scales and mechanisms for kinetic and chemical equilibration of the quark-gluon plasma at zero and non-zero net-baryon density, and elaborate on the connections to jet quenching physics. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700