Bulletin of the American Physical Society
Fall 2022 Meeting of the APS Division of Nuclear Physics
Volume 67, Number 17
Thursday–Sunday, October 27–30, 2022; Time Zone: Central Daylight Time, USA; New Orleans, Louisiana
Session DF: Mini-Symposium: The Initial State of Heavy-Ion Collisions I |
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Chair: Jorge Noronha, University of Illinois at Urbana-Champaign Room: Hyatt Regency Hotel Celestin F |
Friday, October 28, 2022 8:30AM - 9:06AM |
DF.00001: Unraveling the Physics of the Initial State of Heavy-Ion Collisions Invited Speaker: Bjoern P Schenke One of the major uncertainties in the theoretical description of heavy ion collisions is the initial state, typically referring to how energy, momentum, and conserved charges are deposited in space immediately after the collision. Computing such initial states involves descriptions of the incoming nuclei at high energy, and a mechanism for energy, momentum and charge deposition. I will review the state of the art in modeling the initial state with focus on the color glass condensate effective theory, the use of Bayesian analyses to extract initial state properties, and how small systems can give additional insight into the details of the initial state. I will discuss how the increasing experimental precision in heavy ion collisions provides us with new access to nuclear structure at high energy, including detailed information on nuclear deformation and the size of fluctuating nuclear constituents. Finally, I will comment on the transition to hydrodynamics and what we know about the pre-equilibrium stage in heavy ion collisions. |
Friday, October 28, 2022 9:06AM - 9:18AM |
DF.00002: Assessing the ultra-central flow puzzle in the Bayesian era MaurĂcio Hippert, AndrĂ© Veiga Giannini, Mauricio Narciso Ferreira, David Dobrigkeit Chinellato, Gabriel S Denicol, Matthew Luzum, Jorge Noronha, Tiago Nunes da Silva, Jun Takahashi An outstanding problem in heavy-ion collisions is the inability for models to accurately describe ultra-central experimental flow data, despite that being precisely the regime where a hydrodynamic description is most applicable. We reassess the status of this puzzle by computing the flow in ultra-central collisions obtained from multiple recent Bayesian models that were tuned to various observables in different collision systems at typical centralities. While central data can now be described with better accuracy than in previous calculations, tension with experimental observation remains and worsens as one goes to ultra-central collisions. Tuning the model parameters cannot remove this tension without destroying the fit at other centralities. Our results show that the ultra-central flow puzzle cannot be resolved by state-of-the-art simulations, suggesting that modifications are needed in the standard modeling of heavy-ion collisions. |
Friday, October 28, 2022 9:18AM - 9:30AM |
DF.00003: Precision initial condition via nuclear structure imaging technique in high-energy heavy-ion collisions Jiangyong Jia The hydrodynamic modeling of the quark-gluon plasma (QGP) permits us today not only to perform quantitative extractions of the transport properties of the QGP, but also to strongly constrain its initial condition. A growing body of experimental evidence shows that the QGP initial condition is strongly impacted by the shape and radial structure of the colliding nuclei. We discuss the exciting prospect of using precision flow measurements as a tool to image the structure of atomic nuclei, and show how such measurements probe the quadrupole, octupole, and triaxial deformations of the colliding ions, as well as their neutron skin. Motivated by recent groundbreaking measurements from RHIC and LHC, we discuss in particular the case of collisions of isobaric nuclei, which provide a clean access route to the collective structure of the colliding ions. We discuss the implications of nuclear structure on the initial condition of heavy ion collisions as well as the complementarity to the low-energy experiments. We argue that a scan of stable isobars at high-energy colliders may open a new exciting direction of research in nuclear physics. |
Friday, October 28, 2022 9:30AM - 9:42AM |
DF.00004: Probing nuclear deformation at LHC energies using AMPT Somadutta Bhatta Deformation in nuclear geometry arises from collective motion of nucleons and are generally estimated by measuring transition probabilities between low-lying nuclear rotational states. Recent experimental and theoretical developments have established that multi-particle correlations in heavy-ion collisions are also sensitive to nuclear deformation parameters owing to the small time-scale involved in such events. This presentation shows the dependence of various 2, 3 and 4-particle flow correlations in heavy ion collisions on the deformation parameters of the nucleus using A Multi Phase Transport Model (AMPT) for heavy ion collisions at LHC energies. This work establishes consistency across RHIC and LHC energies on the sensitivity of heavy ion observables towards deformation in nuclear geometry. |
Friday, October 28, 2022 9:42AM - 9:54AM |
DF.00005: Probing Effect of Nuclear Shape Coexistence in Heavy-Ion Collisions using Glauber Model Aman Dimri, Somadutta Bhatta, Jiangyong Jia The effect of deformation in nuclear geometry on both initial and final state observables has been reported by recent theoretical developments as well as experimental studies. However, in addition to fixed nuclear deformation, the nuclear geometry can manifest "Shape Coexistence" as evident from low-energy spectroscopic measurements. This study aims to quantify the effects of shape coexistence in heavy-ion collisions using the Glauber model. The effect of shape coexistence on the initial state observables such as eccentricity and area fluctuations are reported in this work. |
Friday, October 28, 2022 9:54AM - 10:06AM |
DF.00006: Effect of Fine Radial Structure in Nuclear Density Distributions on Heavy-Ion Collison Observables Zhengxi Yan The final state observables in heavy-ion collisions depend critically on the states of initial ions, which are governed by the nuclear density distributions. A common approach for modeling a density distribution is to estimate it with a 2-parameter Fermi function (2PF), but as the precision of the measurement increases, the detail smoothed out by the approximation becomes significant. We incorporate the fine radial structure of the density distribution from density functional theory calculations, focusing on the unevenness of the radial distribution rather than the half-height radius or skin depth differences. Using Monte Carlo Glauber simulation, we measure the effect of the fine radial structure on the eccentricity observables, and participant nucleon distributions. We report a difference on the order of 1% compared to the 2PF approximation. This indicates that the fine radial structure needs to be taken into account for high-precision modeling. |
Friday, October 28, 2022 10:06AM - 10:18AM |
DF.00007: The scientific case for and against baryon junctions James Nagle Baryon junctions are a conjectured gluon configuration that carries the baryon quantum number in baryons - rather than each of the quarks carrying baryon numuber 1/3. Such baryon junctions have been proposed to help explain experimental results on baryon stopping in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions. Recently a resurgence of this proposal has led to a re-examination of past data, as well as ideas for new measurements. In this talk, we examine the scientific case for and against baryon junctions. In particular, we detail the level of scientific scrutiny necessary to claim a discovery in this area. |
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