Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session KJ: Mini-Symposium on How Small is the QGP? Collectivity in Small Systems II |
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Chair: Julia Velkovska, Vanderbilt University Room: City Center A |
Friday, October 27, 2017 2:00PM - 2:12PM |
KJ.00001: Constraints on Three-dimensional Entropy Deposition in Relativistic Heavy-ion Collisions from Longitudinal Multiplicity Observables for pA and AA at the LHC Weiyao Ke, John Moreland, Jonah Bernhard, Steffen Bass Relativistic viscous fluid dynamics (rRFD) has been highly sucessful in describing bulk observables of the QGP formed in ultra-relativistic heavy-ion collisions. However, vRFD requires an initial condition that is challenging to calculate from first-principles. Although reliable boost-invariant (2D) initial conditions are well developed, little is known about the longitudinal structures. We systematically study a parametric model for the initial 3D entropy distribution of the QGP formed in the collisions. We apply a cumulant generating function approach to parametrize the rapidity dependence of local entropy deposition as functions of participant densities, extending the 2D initial condition model TRENTo to 3D. This initial condition is integrated into a 3+1D ideal (for computational expediency) hydrodynamic model and a hadronic afterburner to calculate the centrality dependent charged particle pseudorapidity density and two-particle pseudorapidity correlation. Parameters are optimized by comparing to experimental measurements for p+Pb and Pb+Pb collisions using Bayesian inference. Finally, we use the calibrated model and a 3+1D viscous hybrid model to predict pseudorapidity dependent flows, event-plane decorrelations and flow correlations beyond mid-rapidity as a validation. [Preview Abstract] |
Friday, October 27, 2017 2:12PM - 2:24PM |
KJ.00002: Azimuthal Angle correlations in Large and Small Systems - Why the fuss? Roy Lacey In this talk, I will discuss recent momentum anisotropy measurements for a broad range of systems at both RHIC and LHC energies. In particular, the respective roles of final state effects versus initial state momentum domain effects in explanations of the measurements, will be addressed. I will also discuss how these measurements can be leveraged to constrain the properties of the medium produced in these collisions. [Preview Abstract] |
Friday, October 27, 2017 2:24PM - 2:36PM |
KJ.00003: Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC Jie Zhao The chiral magnetic effect (CME) is a fundamental property of QCD. A major background source for CME measurements is the intrinsic particle correlations (such as resonances/jets decay) coupled with the azimuthal elliptical anisotropy $v_{2}$. In heavy-ion collisions, the magnetic field direction and event plane azimuthal angle $\Psi_{2}$ are correlated, thus the CME and the $v_{2}$-induced background are entangled. In small system p+Au and d+Au collisions, the $\Psi_{2}$ is mostly due to geometry fluctuations, and thus magnetic field direction and $\Psi_{2}$ are uncorrelated. The correlation measurements in small system collisions with respect to $\Psi_{2}$ are only sensitive to $v_{2}$-induced background while any CME is averaged to zero. In this talk, we will present the STAR measurements of two-particle correlations with respect to $\Psi_{2}$ in p+Au, d+Au and Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. These results are analyzed as a function of particle multiplicity to shed light on the background contaminations of the CME measurements in heavy-ion collisions. We will also report results from a new analysis approach as a function of the particle pair invariant mass in order to suppress non-CME related physics backgrounds. [Preview Abstract] |
Friday, October 27, 2017 2:36PM - 2:48PM |
KJ.00004: New insights on the chiral magnetic effect from small systems at CMS Wei Li Studies of charge-dependent azimuthal correlations for same- and opposite-sign particle pairs are presented in PbPb collisions at 5 TeV and pPb collisions at 5 and 8.16 TeV, with the CMS experiment at the LHC. The azimuthal correlations are evaluated with respect to the second- and also higher-order event planes. By employing an event-shape engineering technique, the dependence of correlations on azimuthal anisotropy flow is investigated. New results presented by comparing large and small systems provide new insights to the origin of observed charge-dependent azimuthal correlations, and have important implications to the search for the chiral magnetic effect in heavy ion collisions. [Preview Abstract] |
Friday, October 27, 2017 2:48PM - 3:00PM |
KJ.00005: Multiplicity evolution of identified particle charge-dependent correlations in Pb-Pb, p-Pb and pp collisions at the LHC with ALICE Jinjin Pan The charge pair creation and transport processes in heavy-ion collisions are investigated experimentally by measurements of charge-dependent correlations of identified particle pairs, related to the Balance Function[1]. The produced pair separation in rapidity is expected to be larger for hadrons arising from quark-antiquark pair creation in the early stages of the collision than for hadrons emerging from the later hadronization stage. Correlations are reported for charged-pion pairs in Pb-Pb, p-Pb and pp collisions at $\surd $s$_{\mathrm{NN}}=$2.76, 5.02 and 7 TeV, respectively; and for charged-kaon pairs in Pb-Pb collisions at $\surd $s$_{\mathrm{NN}}=$2.76 TeV. The correlations are measured as a function of relative rapidity $\Delta $y and azimuthal angle $\Delta \phi $, and are dominated by a peak centered at $\Delta $y$=\Delta \phi =$0. We observe that the peak widths in $\Delta $y and $\Delta \phi $ are narrower in higher multiplicity events in Pb-Pb, p-Pb, and pp collisions, which is consistent with the effects of radial flow, as well as the two-wave quark production mechanism. We investigate the charge transport and system evolution further by studying the $\Delta \phi $ width of the peak as a function of $\Delta $y. [1]Pratt,PRC85(2012)014904 [Preview Abstract] |
Friday, October 27, 2017 3:00PM - 3:12PM |
KJ.00006: Measurement of long-range correlations between muons and charged-particles in $p$Pb with the ATLAS detector Xiao Tu Two-particle correlations between charged-particle pairs and between charged-particle and muon pairs are measured as a function of pseudorapidity and azimuthal angle difference in $p$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV. Structure in the two-dimensional function centered at $\Delta\phi$ = 0 and extending over a large range of $\Delta\eta$ called “ridge” is seen in the data set. A template fitting method is implemented to extract the second Fourier coefficient of the long-range correlations. In this method a rescaled correlation function from peripheral events representing the recoil component plus a cosine modulation representing the ridge is used to describe the whole correlation function. In the analysis $v_{2,2}$ is factorized into the products of the single particle $v_2$. Therefore $v_2$ of the muons is obtained and its dependences on multiplicity and muon transverse momentum are presented. [Preview Abstract] |
Friday, October 27, 2017 3:12PM - 3:24PM |
KJ.00007: Open heavy-flavour production in p--Pb collisions measured with ALICE at the LHC Annelies Veen Heavy quarks (charm and beauty) are valuable probes for the study of the properties of the Quark-Gluon Plasma formed in high energy Pb--Pb collisions, since they are produced in hard scattering processes in the initial stages of the collision. In p--Pb collisions the production of open heavy flavour can be influenced by Cold Nuclear Matter effects (CNM), such as shadowing, $k_T$ broadening and initial-state energy loss. Studies of the effects on the heavy flavour production in p--Pb, in comparison to that in Pb--Pb collisions, makes it possible to distinguish between cold- and hot-nuclear matter effects.\\ The open heavy-flavour production is measured in ALICE at the LHC at mid-rapidity via D-meson reconstruction in hadronic decay channels and electrons from heavy-flavour hadron decays, and at forward rapidity via muons from heavy-flavour hadron decays. In this contribution, we present recent measurements on heavy flavour production from p--Pb collisions at $\sqrt{s_{\rm{NN}}}=$5.02 TeV collected during Run I and Run II of the LHC. Focussing in particular on the D-meson production cross-section and nuclear modification factor, heavy flavour electron and muon results and possible angular correlations, compared to theoretical model predictions. [Preview Abstract] |
Friday, October 27, 2017 3:24PM - 3:36PM |
KJ.00008: Partial Thermalization of Correlations in pA and AA collisionss Sean Gavin, George Moschelli, Christopher Zin Correlations born before the onset of hydrodynamic flow can leave observable traces on the final state particles. Measurement of these correlations can yield important information on the isotropization and thermalization process. Starting with Israel-Stewart hydrodynamics and Boltzmann-like kinetic theory in the presence of dynamic Langevin noise, we derive new partial differential equations for two-particle correlation functions [1,2]. To illustrate how these equations can be used, we study the effect of thermalization on long range correlations. We show quite generally that two particle correlations at early times depend on S, the average probability that a parton suffers no interactions. We extract S from transverse momentum fluctuations measured in Pb+Pb collisions and predict the degree of partial thermalization in pA experiments. [1] S. Gavin, G. Moschelli, C. Zin, Phys. Rev. C 94, 024921 (2016). [2] S. Gavin, G. Moschelli, C. Zin, Phys. Rev. C 9, 064901 (2017). [Preview Abstract] |
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