Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session C13: Ultra-relativistic Heavy Ions |
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Sponsoring Units: DNP Chair: Dennis Perepelitsa, University of Colorado Room: Sheraton Plaza Court 2 |
Saturday, April 13, 2019 1:30PM - 1:42PM |
C13.00001: Anisotropic hydrodynamics approach to dilepton emission from quark-gluon plasma Babak Salehi Kasmaei, Michael Strickland Dileptons can provide information about different stages of evolution of the matter generated in heavy-ion collisions. Particularly, emission of the intermediate-mass dileptons are affected by statistical properties of the quark-gluon plasma. To model the evolution of a non-equilibrium quark-gluon plasma, relativistic anisotropic hydrodynamics takes into account the anisotropy of momentum distributions of the system constituents. We convolve the anisotropic hydrodynamic evolution with the local rest frame production rates of dileptons modified by the momentum anisotropic medium to calculate the differential yield and elliptic flow of dileptons emitted from quark-gluon plasma. We investigate effects of the model parameters on the observable quantities that can be extracted from heavy-ion collision experiments. |
Saturday, April 13, 2019 1:42PM - 1:54PM |
C13.00002: GPU-Accelerated Computation of Femtoscopic Correlation Functions for Heavy-Ion Collisions Sameed Pervaiz, Christopher Plumberg, Ulrich W Heinz Since its discovery, Hanbury-Brown Twiss (HBT) interferometry has served as an invaluable tool to particle physicists by allowing the precise measurement of spatio-temporal quantities of various particle-emission sources that are otherwise difficult to probe directly. In our study of Quark-Gluon Plasma (QGP), we overcome challenges posed by the small time and length scales (10e-23 s and 10e-15 m, respectively) involved in relativistic heavy ion collisions by analyzing average quantum correlation effects affecting the resulting particle shower from the QGP's hadronization. By computing the expected correlation functions and comparing them to experimental statistics, we are able to test the current theory of QGP's dynamics. However, as HBT calculations often suffer from poor serial performance, we directed our research on using conventional graphics processors to parallelize HoTCoffeeh, a C++ application created for calculating correlation functions (CFs) in 2+1D. Results indicate that our CF calculations decompose into several embarassingly parallelizable subproblems, leading to major computation time savings that allow larger quantities of events to be generated and analyzed than previously feasible in conventional supercomputing and grid computing environments. |
Saturday, April 13, 2019 1:54PM - 2:06PM |
C13.00003: Model studies of two-particle correlations in small and large collision systems Sedigheh Jowzaee The models UrQMD, AMPT and Hijing were used to study the two-particle correlations of identified hadrons in Au+Au collisions over a range of beam energies from 7.7 to 200 GeV at RHIC. The angular correlations of like-sign and unlike-sign mesons (π and K) and baryons (p) were measured allowing the contributions of different physics mechanisms to the observed correlations to be inferred. The model results will also be compared to preliminary experimental results from the STAR Collaboration which exhibit positive short-range correlations in two meson pairs, and a strong anticorrelation in proton pairs. The two particle correlations will also be presented for the small system of p+p at 200 GeV using different versions of the Pythia model. The implications of such model studies for the understanding of the two-particle correlations in both small and large systems will be discussed. |
Saturday, April 13, 2019 2:06PM - 2:18PM |
C13.00004: Longitudinal Flow Correlations in Xe-Xe Collisions at √sNN = 5.44 TeV with the ALICE Detector Raquel Quishpe, Anthony R. Timmins Anisotropic flow in relativistic heavy-ion collisions has been studied as a signature of the quark gluon plasma (QGP). For different colliding systems, anisotropic flow has been described by the decomposition of azimuthal correlations into Fourier coefficients, vn. More precisely, the second and third harmonics, v2 and v3, describe the eccentricity of the initial state and the response to the medium. In 2017, Xe-Xe collisions took place in the LHC at √sNN = 5.44 TeV. The v2 and v3 coefficients agreed with the expected behavior of the denser medium compared to others, e.g. Pb-Pb (arXiv:1805.01832v1). Furthermore, it has been seen that longitudinal correlations also show anisotropies in the medium which may be used to constrain the medium properties previously mentioned. These longitudinal correlations can be analyzed and described by Legendre Polynomials. For the Xe-Xe collisions data set recorded by ALICE in 2017, results from longitudinal correlations coefficients, an, are presented. |
Saturday, April 13, 2019 2:18PM - 2:30PM |
C13.00005: Measurement of the D0-meson elliptic and triangular flow in Au+Au collisions √sNN = 200 GeV collisions from STAR Yue Liang Azimuthal anisotropic flow coefficients (vn) are valuable tools to study the Quark-Gluon Plasma (QGP) created in heavy ion collisions. Recent results from the STAR experiment show that in 10-40% central Au+Au collisions at the top RHIC energy the elliptic flow (v2) of D0 mesons follow the Number-of-Constituent-Quark(NCQ) scaling in the same way as it does for light-flavor hadrons. This suggests that charm quarks have gained large collectivity through their interactions with the QGP medium. |
Saturday, April 13, 2019 2:30PM - 2:42PM |
C13.00006: Soft and Collective Particle Generator for a Better Understanding of Heavy Ion Background in Jet Studies Charles P Hughes, Alex L Aukerman, Thomas Krobatsch, Adam Matyja, Christine E Nattrass, James C Neuhaus, William E Witt At the Large Hadron Collider (LHC), nuclei are made to collide at near light-speed. These collisions generate a novel phase of matter: the Quark Gluon Plasma (QGP). One set of tools used to study the properties of the QGP are jets. Jets are generated early in the nuclear collision when internal quarks and gluons scatter with high momentum transfer. These quarks and gluons traverse the QGP as it forms, lose energy, and re-hadronize into collimated streams. The main difficulty in measurements of jets is the large background of spatially correlated hadrons due to the multitude of soft collisions from the expansion and cooling of the short lived QGP. We generate a data-driven background for jets based on measurements of soft charged hadron transverse momentum spectra and charged hadron azimuthal flow at the LHC. We use this data-driven background in concert with Monte-Carlo parton shower generators and jet-finding algorithms to better understand how lower momentum jets are modified. We present the current status of these studies. |
Saturday, April 13, 2019 2:42PM - 2:54PM |
C13.00007: Heavy Ion Physics with LHCb J Matthew Durham The LHCb experiment at the Large Hadron Collider provides a unique facility for the study of heavy ion collisions. LHCb has a precision silicon detector that allows unparalleled measurements of heavy flavor, and is the only detector at the LHC which can measure fully identified particles at forward rapidity. This enables measurements of fully reconstructed charm and bottom mesons and baryons, along with measurements of quarkonia decays to dimuons. In addition, LHCb has the ability to record data on beam collisions with noble gases injected into the interaction region, allowing it to function as a fixed target experiment. An overview of the LHCb heavy ion program will be given, and selected results will be discussed. |
Saturday, April 13, 2019 2:54PM - 3:06PM |
C13.00008: Measurement of Higher Moments of Multiplicity Distributions of Conserved Quantities in the STAR Experiment at RHIC. Debasish Mallick The higher moments of multiplicity distributions of the net proton (proxy for net baryon), net kaon (proxy for net strangeness) and net charge are expected to show large fluctuations near the QCD critical point. The STAR experiment performed measurements of various higher order moments and moments products of net proton, net charge and net kaon distributions in Au+Au collisions as a function of collision energy (√sNN = 7.7 - 200 GeV) in the Beam Energy Scan I (BES-I) program.
We will present results on collision energy and centrality dependence of higher moments of the net proton, net kaon and net charge multiplicity distribution over all BES-I energies from STAR. In the most central (0-5%) collisions, the κσ2 of net proton distribution as a function of collision energy exhibit a non-monotonic behaviour and shows deviation in the lower energy region from corresponding predictions from a Poisson baseline, a transport model and a thermal model, none of which include any physics of criticality. We will also discuss results from measurements of the ratio of sixth to second order cumulant (C6/C2) of net charge and net proton distributions, motivated towards the search for possible signals of a crossover transition. |
Saturday, April 13, 2019 3:06PM - 3:18PM |
C13.00009: Net-lambda fluctuations in Pb-Pb collisions at √SNN = 5.02 TeV in ALICE at the LHC Ejiro Naomi Umaka The analysis describes the measurement of the first and second cumulants of net-Λ distribution in Pb-Pb collisions at √SNN = 5.02 TeV using the ALICE detector. A fundamental goal of heavy-ion collision experiment is to map out the temperature (Tf) and baryon chemical potential (µBf) parameters of the Quantum chromodynamics (QCD) phase diagram at which chemical freeze-out occurs – a point on the phase diagram when particle species produced are fixed. The cumulants of conserved quantities (net-charge, net-baryon, net-strangeness) are directly related to the quark number susceptibilities calculated with lattice QCD. In a fluctuation analysis, net-pion, net-proton, and net-kaon are typically used as proxies for net-charge, net-baryon, and net-strangeness respectively. The lambda particle consists of a strange quark and it is as well a baryon. Hence, measuring the cumulants of net-Λ provides insight into the fluctuations of net-strangeness and net-baryon number. In addition, the ratios of the net-Λ cumulants used to extract Tf and μBf can be compared to those of net-proton to identify the signature of a flavor hierarchy, that is, if heavier quarks freeze-out at a different Tf and μBf from lighter quarks. |
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