Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session MH: Ultrarelativistic Heavy Ions II |
Hide Abstracts |
Chair: Christopher Plumberg, University of Illinois at Urbana-Champaign Room: Whittier |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MH.00001: Centrality Determination in the Forward Region in the RHIC Beam Energy Scan at STAR Rachael Botsford The quark-gluon plasma (QGP) is a state of matter in which quarks and gluons are not confined into nucleons. A primary goal of the Beam Energy Scan (BES) at the Relativistic Heavy Ion Collider (RHIC) is to uncover information about the transition between QGP and ordinary matter by analyzing heavy-ion collisions at a variety of energies. The centrality of high energy nucleus-nucleus collisions is typically determined by the multiplicity of charged particles in the midrapidity range, which can lead to autocorrelations that affect the observables measured at mid-rapidity. One way to minimize these autocorrelations is to use a forward detector such as the Event Plane Detector (EPD) to determine centrality. However, the centrality resolution of the EPD may be impacted by spectator protons from the collisions. The EPD is made up of 744 scintillator tiles comprising 16 rings. An alternate approach to utilize the EPD for better centrality determination is to consider each EPD ring separately, rather than summing the contribution of the particles over the entire EPD. This talk will attempt to determine the effectiveness of this method using 2019 data from Au+Au collisions with center of mass energy √sNN=19.6 GeV, with an outlook for performance at other BES energies. |
Wednesday, October 13, 2021 4:12PM - 4:24PM |
MH.00002: Measurements of two-particle correlations in e+e- collisions at 91-209 GeV with ALEPH archived data YEN-JIE Lee, Janice Chen, Yi Chen, Marcello Maggi, Pao-Ti Chang Measurements of two-particle angular correlations of charged particles |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MH.00003: Centrality determination with a forward detector in the RHIC Beam Energy Scan Skipper Kagamaster In heavy ion collisions, centrality is the amount of overlap between nuclei in a collision event and is not a direct observable. Various methods are employed by experiments which use different observables as a proxy for centrality, and these centrality proxies form an important eventwise characteristic for many analyses. In the RHIC Beam Energy Scan (BES), centrality is usually determined at mid-rapidity where pseudorapidity η ≤ 1. Determining centrality within this η acceptance, however, could lead to the autocorrelation effect (ACE), which can suppress values such as kurtosis for net proton distributions (κσ2). Forward η centrality determination could be possible with the STAR Event Plane Detector (EPD), which would avoid ACE; however, the presence at lower collision energy (√sNN) of spectator protons from the initial collision complicates an EPD based centrality to the point that, when using a simple ``sum of particles" method, EPD centrality is not of sufficient resolution for use in BES analyses. This talk will discuss a technique of linearly weighting η rings of the EPD, which rectifies the forward centrality resolution issue. This technique will be demonstrated using UrQMD simulations of Au+Au collisions in the range of √sNN = 7.7-200 GeV. Implications of an EPD based centrality on measured κσ2 will also be discussed, as well as more sophisticated techniques that could be employed to form an EPD centrality measure. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MH.00004: Study of baryon fluctuations in azimuthal phase space and the search for critical phenomena at STAR Dylan Neff Divergence of correlation length is a universal feature of critical phenomena in phase transitions. In the search for a critical point in the QCD phase diagram, such a divergence may be reflected in particle yield fluctuations in phase space. Fluctuations of baryon multiplicities in heavy-ion collisions within a limited pseudo-rapidity range have been used to search for signs of a critical point in the STAR Beam Energy Scan (BES) Phase I data. Particle yield fluctuations arising from critical phenomena would naturally exist in both longitudinal and azimuthal subvolumes of phase space. In this analysis, proton fluctuations in azimuthal subvolumes are investigated via new observables. Mixed events are utilized as a baseline which allows for the measurement of correlation length proxies that are less sensitive to common experimental complications. Measurements of transformed proton multiplicity distributions in azimuthal partitions of Au+Au collisions from the STAR BES-I program will be presented. The kurtosis of these distributions will be shown as a function of beam energy and azimuthal partition size. The observed trends are compared with those obtained from the AMPT model. Future perspective with the STAR BES-II data will also be discussed. |
Wednesday, October 13, 2021 4:48PM - 5:00PM |
MH.00005: Study of event multiplicity and $J/\psi$ production in p+p and p+Au collisions at PHENIX experiment Ming X Liu $J/\psi$ production has been studied extensively in heavy ion collisions at RHIC and other facilities for decades. However, there are still large uncertainties in our understanding of the production mechanisms, and various contributions from the initial and final state effects quantitatively. To gain additional information that could help us to further constrain these uncertainties, we study the impacts of the event multiplicity on the J/ψ production. Specifically, we study the $J/\psi$ yields at the forward and backward rapidities (1.2<|y|<2.2) in 200 GeV p+p and p+Au collisions recorded by the PHENIX experiment at RHIC in the 2015 data taking period, as a function of the event charged track multiplicity in the forward, central, and backward rapidities. The latest status of this study will be presented. |
Wednesday, October 13, 2021 5:00PM - 5:12PM Not Participating |
MH.00006: Two particle correlations of neutral and charged kaons in heavy ion collisions Anjaly Sasikumar Menon Measurements of two particle correlations are sensitive to several characteristics of the medium created in heavy ion collisions. Looking at the correlations of charged and neutral kaons might provide information about the potential formation of disoriented chiral condensates (DCCs). Previous ALICE measurements have indeed shown a strong anti-correlation between charged and neutral kaons, which is qualitatively consistent with the formation of DCCs. The initial goal of this analysis is to perform charged and neutral kaon identification with high purity using the ALICE detector. Once the neutral and charged kaons are cleanly identified, they can be used to construct the two-particle correlation function. We will show measurements of a more differential analysis of these correlations as function of △Φ and △η from Pb-Pb collisions at √sNN = 5.02 TeV. |
Wednesday, October 13, 2021 5:12PM - 5:24PM |
MH.00007: X(3872) and Bc Kinetics in Heavy-Ion Collisions Biaogang Wu, Xiaojian Du, Matthew Sibila, Ralf F Rapp, Zhanduo Tang We investigate the in-medium kinetics of the X(3872) and Bc particles in ultra-relativistic heavy-ion collisions. Toward this end, we employ our well-tested rate equation approach for quarkonia to compute the time evolution of the X(3872) and Bc distributions, each governed by two transport parameters, i.e., the equilibrium limit and inelastic reaction rate. The equilibrium limits of X(3872) and Bc are entirely determined by the particles' masses and the previously calculated charm-quark and bottom-quark fugacities. The reaction rate for the X(3872) is believed to depend on its structure, being "large" for a DD* molecule and "small" for a tetraquark (diquark-antidiquark). The reaction rate of the Bc is calculated in the quasi-free approximation as previously used for charmonia and bottomonia. We evaluate the sensitivity of the final X(3872) abundance and pT spectra on different scenarios for its width and |
Wednesday, October 13, 2021 5:24PM - 5:36PM |
MH.00008: Spin-Orbit Interactions and Heavy-Quark Transport in the QGP Zhanduo Tang, Ralf F Rapp We employ a previously constructed T-matrix approach for heavy-quark (HQ) transport in the quark-gluon plasma (QGP) to compute the effects of spin-orbit interactions between partons. Based on the vacuum Cornell potential, we first confirm that the experimental values of the mass splittings in quarkonium P-wave states are improved by employing a confining potential that is a mixture of vector and scalar potentials rather than a purely scalar one. We then apply the refined potential to calculate the in-medium single-parton spectral functions at finite temperature self-consistently. The temperature corrections to the in-medium potential are constrained by results from thermal lattice-QCD for the HQ free energy and Euclidean correlator ratios of charmonium spectral functions. Finally, we study the in-medium charm quark transport coefficients at different temperatures. It turns out that the mixing effect for confining potential enhances the drag coefficient, A(p), for charm quarks in the QGP over previous calculations with a purely scalar potential, thereby also decreasing the pertinent diffusion coefficients, Ds. Our results thus advance the microscopic description of HQ transport, and are likely to improve the current phenomenology of open heavy-flavor observables at RHIC and the LHC. |
Wednesday, October 13, 2021 5:36PM - 5:48PM |
MH.00009: Spin polarization as a probe for local parity violation Matteo Buzzegoli Due to non-perturbative QCD topological transitions induced by high temperature, the Quark Gluon Plasma generated by ultra-relativistic heavy ion collisions is expected to be created with a chiral imbalance, whose value fluctuates in a event-by-event basis. In other words, we expect a local breaking of parity symmetry in hot QCD matter. However, this has never been observed. The search for local parity violation is primarily carried out through the Chiral Magnetic Effect that requires an accurate estimate of the magnetic filed generated during the collisions. There is an ongoing dedicated isobar run to search for this effect at Relativistic Heavy Ion Collider. In this talk, I will show that local parity violation due to chiral imbalance can also be revealed, without relying on the knowledge of the magnetic field, by measuring the projection of the polarization vector onto the momentum, i.e. the helicity, of final state baryons. I will show that the polarization of spin 1\2 baryons receives an additional contribution along their momentum proportional to the chiral chemical potential. This additional, parity-breaking, contribution to helicity can be detected by studying the helicity-helicity correlation of two particles with large azimuthal angle difference. |
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