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 FB: Ultrarelativistic Heavy Ions |
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Chair: Christine Nattrass, University of Tennessee Room: Salon 2 |
Thursday, October 26, 2017 4:00PM - 4:12PM |
FB.00001: Anisotropic hydrodynamic modeling of 2.76 TeV Pb-Pb collisions Mubarak Alqahtani, Michael Strickland In this talk, I will present some comparisons of phenomenological results from 3+1d quasiparticle anisotropic hydrodynamics (aHydroQP) with experimental data collected in LHC 2.76 TeV Pb-Pb collisions. In particular, I will present comparisons of particle spectra, average transverse momentum, and elliptic flow. This new model relies on the introduction of a single temperature-dependent quasiparticle mass which is fit to lattice QCD data. The dynamical equations can be obtained by taking moments of Boltzmann equation which are used in the hydrodynamic stage. In this work, we include the effects of both shear and bulk viscosities. At freeze-out, we use anisotropic Cooper-Frye freeze-out performed on a fixed-energy-density hypersurface to convert to hadrons. To model the production and decays of the hadrons we use THERMINATOR 2 which is customized to sample from ellipsoidal momentum-space distribution functions. Using smooth Glauber initial conditions, we find very good agreement with many heavy-ion collision observables. [Preview Abstract] |
Thursday, October 26, 2017 4:12PM - 4:24PM |
FB.00002: Search for gluon saturation at Bjorken-x of 10$^{-6}$-10$^{-5}$ with the LHCb detector. Cesar Da Silva Gluon saturation at small Byorken-$x$ has been in the minds of particle and nuclear physicists for decades. This state can explain several recent observations such as 1) particle collectivity observed in p+p, p+A and A+A collisions at RHIC and LHC; and 2) depleted yield of particles coming from soft gluons. Previous results from DIS experiments at HERA show a fast increase of gluons as their fractional momentum $x$ decreases. The LHCb experiment is a forward spectrometer with vertexing, tracking, $p$, $K$, $pi$, $e$, $\mu$ identification and calorimetry in the rapidity region 1.6$< \eta <$ 4.9. LHCb is the only experiment in the world which can probe $x \sim 10^{-6}-10^{-5}$, up to two orders of magnitude smaller than HERA. A direct probe of gluons at small-x and small $Q^2$ can be performed with $\gamma$+jet correlation measurements. The current detector acceptance is not optimized for soft particles coming from $Q^2<$10 [GeV/c]$^2$ processes, where gluon saturation is expected. R&D is underway for a new tracking detector to be placed inside the LHCb magnet, the Magnet Station (MS), which will enable measurements of these soft particles. This talk is going to report the status of the analysis efforts aimed at finding the gluon saturation scale at LHCb, and details of the MS. [Preview Abstract] |
Thursday, October 26, 2017 4:24PM - 4:36PM |
FB.00003: Studying Cold Nuclear Matter with the MPC-EX of PHENIX Nathan Grau Highly asymmetric collision systems, such as $d$+Au, provide a unique environment to study cold nuclear matter. Potential measurements range from pinning down the modification of the nuclear wave function, i.e.~saturation, to studying final state interactions, i.e.~energy loss. The PHENIX experiment has enhanced the muon piston calorimeter (MPC) with a silicon-tungsten preshower, the MPC-EX. With its fine segmentation the MPC-EX extends the photon detection capability at 3$<|\eta|<$3.8. In this talk we review the current status of the detector, its calibration, and its identification capabilities using the 2016 $d$+Au dataset. We also discuss the specific physics observables the MPC-EX can measure. [Preview Abstract] |
Thursday, October 26, 2017 4:36PM - 4:48PM |
FB.00004: The sPHENIX Experiment at RHIC John Haggerty The proposed sPHENIX experiment at RHIC will make high statistics measurements of jets, jet correlations, and upsilon states in heavy ion collisions in the early 2020's. High resolution tracking coupled with uniform electromagnetic and hadronic calorimetry will be used to characterize the temperature dependence of transport coefficients of the quark-gluon plasma. Progress on the design of the detector, test results of prototypes, and expectations from full detector simulation which demonstrate the capabilities of the experiment will be presented. [Preview Abstract] |
Thursday, October 26, 2017 4:48PM - 5:00PM |
FB.00005: Calculating Fragmentation Functions in Heavy Ion Physics Simulations Charles Hughes, Alex Aukerman, Thomas Krobatsch, Adam Matyja, Christine Nattrass, James Neuhaus, Soren Sorensen, William Witt A hot dense liquid of quarks and gluons called a Quark Gluon Plasma (QGP) is formed in high energy nuclear collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider. The high energy partons which scatter during these collisions can serve as probes for measuring QGP bulk properties. The details of how partons lose energy to the QGP medium as they traverse it can be used to constrain models of their energy loss. Specifically, measurements of fragmentation functions in the QGP medium can provide experimental constraints on theoretical parton energy loss mechanisms. However, the high background in heavy ion collisions limits the precision of these measurements. We investigate methods for measuring fragmentation functions in a simple model in order to assess their feasibility. We generate a data-driven heavy ion background based on measurements of charged hadron transverse momentum spectra, charged hadron azimuthal flow, and charged hadron rapidity spectra. We then calculate fragmentation functions in this heavy ion background and compare to calculations in proton-proton simulations. We present the current status of these studies. [Preview Abstract] |
Thursday, October 26, 2017 5:00PM - 5:12PM |
FB.00006: Photon-hadron correlations and jet fragmentation in Au+Au 200 GeV collisions measured with PHENIX Zachary Rowan Because of the observed jet suppression in heavy ion collisions, typical jet reconstruction, or high pt hadron jet tagging, results in a surface bias. Prompt photons, produced in the Compton scattering and annihilation of quarks, easily escape the quark gluon plasma and, when used to tag away side jets, introduce no such bias. However a bias towards quark jets is introduced as the Compton production process dominates, making these tagging methods complimentary. With the additional benefit of the photon $p_T$ being a suitable proxy for the jet $p_T$, photon-hadron correlations in Au+Au 200 GeV collisions are analyzed with PHENIX. Through the analysis of mixed events with reaction plane classification, the background contribution to the azimuthal correlation function can be removed, revealing an away side jet peak. By characterizing the structure in multiple centrality classes; photon emission angles measured with respect to reaction plane orientation; and photon energies, the collision geometry and relative levels of bremsstrahlung and fragmentation photons can be varied, allowing for a detailed study of path length dependent jet fragmentation. The status of this analysis will be discussed. [Preview Abstract] |
Thursday, October 26, 2017 5:12PM - 5:24PM |
FB.00007: Photon - Hadron Correlations in Heavy Ion Collisions from PHENIX Tyler Danley Direct photon-jet pairs are produced in the initial hard scattering of nucleons in A+A collisions in which a quark-gluon plasma is formed. The photon is not affected by the quark-gluon plasma, while the jet loses energy. This allows the direct photon to be an energy calibrator for the jet which can then be studied through photon-hadron pair correlations. Obtaining direct photons is challenging because of the myriad of background photons. Typically, a statistical subtraction method is used in A+A at RHIC. In addition to a statistical method, we have also developed a direct method to obtain isolated photons in A+A by using an isolation cut like those used in direct photon identification in p+p collisions. The isolation cut provides for a cleaner sample of direct photons, potentially reducing the systematic uncertainties on direct photon-hadron correlations when compared to the statistical subtraction sample but presents its own new challenges in the A+A high multiplicity environment. We present the status of centrality-dependent direct photon-hadron angular correlations and fragmentation functions in A+A collisions as well as recent results from recent high-statistics PHENIX datasets. [Preview Abstract] |
Thursday, October 26, 2017 5:24PM - 5:36PM |
FB.00008: Di-jet Hadron Correlations in Central Au+Au Collisions at $\sqrt{s_{NN}}=200$ GeV at STAR Nicholas Elsey Jets and their modifications due to partonic energy loss provide a powerful tool to study the properties of the QGP created in ultrarelativistic heavy-ion collisions.\\ For jets reconstructed with the anti-$k_T$ algorithm with resolution parameter $R=0.4$, previous measurements of the di-jet asymmetry $A_J$ at STAR\cite{A} indicate that the observed imbalance of an initial ``hard-core" di-jet selection with $p_T^{\mathrm{const}}>2.0$ GeV/c, $p_T^{\mathrm{lead}}>20.0$ GeV/c and $p_T^{\mathrm{sub}}>10.0$ GeV/c is restored to the balance of the pp reference when soft constituents are included. The lost energy recovered with soft constituents suggests soft gluon radiation by high $p_{T}$ partons.\\ Jet-hadron correlations with respect to di-jets allow a differential assessment of the kinematic properties of the soft gluon radiation spectrum induced by partonic energy loss in the QGP. We present charged hadron correlations with respect to the di-jets found in the above $A_J$ analysis, and compare to similar measurements using a jet trigger at RHIC\cite{B}.\\ \\L. Adamczyk {\it et al.} (STAR), arXiv:1609.03878 [nucl-ex]. \bibitem{B} L. Adamczyk {\it et al.} (STAR), Phys.\ Rev.\ Lett.\ {\bf 112}, 122301 (2014). [Preview Abstract] |
Thursday, October 26, 2017 5:36PM - 5:48PM |
FB.00009: Dual-Differential Cross Section Measurements for Inclusive Jets in pp Collisions at $\sqrt{s}=5\ TeV$ with the CMS Detector Ian Laflotte, John Strologas, Raghav Kunnawalkam Elayavalli, Sevil Salur, Owen Baron Jets, collimated high-energy showers of particles, act as proxies for hard scattered partons in pp, pPb, and PbPb collisions as seen by the CMS detector. Though at minimum, jets related to partonic degrees of freedom, fully reconstructed anti-$k_{t}$ Particle Flow jets are subject to significant intermediate and final state effects, including but not limited to; radiation, fragmentation, underlying event background, and detector/reconstruction inefficiencies. Such effects can artificially alter rates of jet production across commonly utilized ranges of jet transverse-momentum, rapidity, and radii. A variety of high-energy physics measurements use fully reconstructed jets, thus, parameterizing intermediate and final state effects is paramount to providing a solid foundation for both past and future jet measurements. In this presentation, preliminary measurements of the dual-differential jet production cross section in pp collisions at center-of-mass energy 5 TeV are shown for small radii, anti-$k_{t}$ Particle Flow jets in a large rapidity window, as observed with the CMS detector. Future extensions featuring a wider range of jet radii and direct comparisons with theoretical NLO and NNLO jet production calculations are planned. [Preview Abstract] |
Thursday, October 26, 2017 5:48PM - 6:00PM |
FB.00010: ABSTRACT WITHDRAWN |
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