Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session NG: Ultrarelativistic Heavy Ions III |
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Chair: Bjorn Schenke, Brookhaven National Laboratory Room: 105AB |
Saturday, October 29, 2011 10:30AM - 10:42AM |
NG.00001: $\pi^{0}$\ production in p+p and Pb+Pb collisions at the LHC Jocelyn Mlynarz We report results of the $\pi^{0}$\ reconstruction in p+p and Pb+Pb at $\sqrt(S_{NN})$ = 2.76 TeV collisions at the LHC, using invariant mass and shower shape analysis based on signals from the ALICE EMCal and PHOS electromagnetic calorimeters, and $e^{+}e^{-}$ conversion pair reconstruction with the central tracking system. We present measurements of the $\pi^{0}$ production cross section as a function of transverse momentum and the neutral pion elliptic flow compared with the $v_{2}$ of charged pions. We use the measured spectra to determine the nuclear modification factor, $R_{AA}$, of Pb+Pb collisions which we compare to theoretical predictions, results from RHIC as well as from the charged pion analysis, showing a strong supression of the $\pi^{0}$ spectrum at high-$p_{T}$. [Preview Abstract] |
Saturday, October 29, 2011 10:42AM - 10:54AM |
NG.00002: Jet-underlying event studies with ALICE detector at the LHC Betty Abelev Relativistic heavy ion collisions produce a state of strongly interacting matter of quarks and gluons, called the Quark Gluon Plasma (QGP). Measuring particle production via fragmentation (specifically in jets) and understanding parton energy loss in the QGP enables one to directly probe the medium. One of the necessary components in studying jets in heavy ion events is the ability to isolate jets from the soft physics background, i.e., the underlying event. Thus it is important to understand the underlying event properties, in particular, energy fluctuations. This presentation will address the initial studies done to map out the underlying event in $\sqrt{s}=7$ TeV pp collisions measured with the ALICE detector at the LHC, as preparation for extending these studies to Pb-Pb collisions. The focus will be on the analyses performed with the ALICE Electro-Magnetic Calorimeter (EMCal). EMCal is especially well-suited for the measurement of high-momentum particles which are produced predominantly in jets and therefore is a useful tool in subtracting the jet cone from the underlying event. [Preview Abstract] |
Saturday, October 29, 2011 10:54AM - 11:06AM |
NG.00003: Electrons from B-meson semileptonic decay in 2.76 TeV p-p collisions identified by the ALICE EMCal Tomas Aronsson High-energy heavy ion (HI) collisions at the LHC allow physicists to study the properties of the quark-gluon plasma (QGP). Heavy quarks produced in the hard-scattering of the HI collision are excellent probes of the QGP. When they traverse the QGP the heavy quarks are expected, according to pQCD, to suffer an energy loss per unit distance proportional to the inverse of the quark mass. Experimental data from RHIC indicate small or no such mass dependence. Beauty quarks, which are considered heavy quarks, produce hadrons with a relatively long lifetime ($c_{\tau}$ $\sim$ 100 - 500 $\mu$m). The semileptonic decay of these hadrons can be identified against the background by secondary vertex reconstruction from high momentum electrons and associated hadrons. The ALICE EMCal detector possesses outstanding particle identification for electrons at high transverse momentum $p_T$. This in combination with the ALICE central tracking detectors provides identification of secondary verticies from semileptonic decay of B-mesons. The electron associated with the secondary vertex is then tagged as a B-electron and the resulting B-jets can be used to extract information on the transport properties of the QGP. In this talk we present initial studies of the identification of electrons from B-meson decay by using primarily the EMCal in the ALICE experiment from p-p data. The data analyzed is 2.76 TeV p-p collisions recorded in 2011 which is to be compared to Pb-Pb collisions in order to determine the effects of the medium. [Preview Abstract] |
Saturday, October 29, 2011 11:06AM - 11:18AM |
NG.00004: Heavy flavor electrons in $\surd $s = 2.76 TeV p-p collisions using the ALICE detector Bernard Hicks Recent measurements from RHIC and the LHC seem to confirm T.D.Lee's hypothesis that a hot and dense strongly interacting matter, the quark-gluon plasma (QGP), could be formed in heavy-ion collisions at high energies. Perturbative QCD predicts that high energy partons passing through a QGP will loose a fraction of their energy (jet quenching) proportional to the density and the traversed distance in the medium. Moreover, for quarks, the amount of the energy lost to the medium depends on their flavor and is inversely proportional to their mass. Heavy quarks (b and c) being formed in the early stages of heavy-ion collisions, are a good probe for the properties of the QGP and allow to study the predicted flavor dependence of jet quenching. Consequently, the spectrum of electrons from the semi-leptonic decays of heavy quarks at intermediate/high p$_{T}$ can provide additional constraints to the theoretical descriptions of the energy loss mechanism. Electrons are identified using the ALICE Electro-Magnetic Calorimeter (EMCal) in conjunction with the mid-rapidity tracking detectors, the Inner Silicon Tracker (ITS) and the Time Projection Chamber (TPC). The major sources of background electrons, such as those from photonic decays, are identified and then subtracted to produce a non-photonic electron spectrum. We present studies towards the crucial reference measurement of the production cross-sections of electrons from b and c decays from pp collisions at $\surd $s=2.76 TeV at the LHC reconstructed in ALICE. [Preview Abstract] |
Saturday, October 29, 2011 11:18AM - 11:30AM |
NG.00005: Heavy flavor electron $v_{2}$ in Au$+$Au Collisions at $\sqrt{s_{NN}}$=62.4 GeV Lei Ding Heavy quarks are produced early in relativistic heavy ion collisions and propagate through and interact with the medium created in the collisions. The measurement of azimuthal anisotropy $v_{2}$ of single electrons from semi$-$leptonic decay of open heavy flavor mesons in PHENIX experiment has provided important understanding of the geometrical dependence of partonic energy loss. PHENIX results of $v_{2}$ in Au$+$Au collision at $\sqrt{s_{NN}}$=200GeV for heavy-flavor decays are comparable to the $v_{2}$ measurements of other hadrons, which is not well understood. We extend the PHENIX systematic study of azimuthal anisotropy by reducing the beam energy to $\sqrt{s_{NN}}$=62.4GeV. We will present $v_{2}$ of heavy flavor electrons at 62.4GeV. [Preview Abstract] |
Saturday, October 29, 2011 11:30AM - 11:42AM |
NG.00006: Measurement of Upsilon suppression in Au+Au collisions at 200 GeV Shawn Whitaker Understanding the quarkonium suppression mechanisms of the QGP is one of the outstanding challenges for theorists and experimentalists at RHIC. Measuring several states in the charmonium and bottomonium families is predicted to provide an indication of the temperature of the plasma since in a hot medium less tightly bound states are predicted to dissociate at lower temperatures than the more tightly bound ground states. A large sample of Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV was collected during 2010 data taking run with the PHENIX detector at RHIC. From this sample $\Upsilon$ yields at mid-rapidity from the di-electron decay channel were determined and used to calculate its nuclear modification factor. [Preview Abstract] |
Saturday, October 29, 2011 11:42AM - 11:54AM |
NG.00007: The elliptic flow of di-leptons in 200 GeV Au+Au collisions at STAR Xiangli Cui Di-leptons are ideal probes of the strongly interacting hot, dense medium created at RHIC. They are not affected by the strong interaction once produced, therefore they can probe the whole evolution of the collision.The di-lepton spectra in the intermediate mass range are directly related to thermal radiation of the QGP. In the low mass range, we can study the vector meson in-medium properties through their di-lepton decays, the observable of possible chiral symmetry restoration. In addition to the spectrum, the elliptic flow of di-leptons, which is sensitive to the early time dynamics, might also shed light on the properties of the medium. In year 2010, a large amount of data were taken in 200 GeV Au+Au collisions with the full time-of-flight detector in operation, which enables the elliptic flow measurements of di-leptons. In this poster, we will present the details of the analysis including background subtraction and elliptic flow methodology. The status of the elliptic flow measurements of di-leptons from low to intermediate mass region will be presented in 200 GeV Au+Au collisions. [Preview Abstract] |
Saturday, October 29, 2011 11:54AM - 12:06PM |
NG.00008: Tagging Jets with Heavy Flavor using the PHENIX VTX Detector Alexander Shaver To better understand the behavior of hadron jets containing heavy flavor (charm, beauty), measurements by a silicon vertex detector (VTX) will be used to tag jets reconstructed by the anti-k$_{T}$ algorithm. The VTX provides precise measurements of particle tracks near the vertex, and allows us to determine quantities such as reconstructed secondary vertices, and the distance of closest approach of each track to the collision vertex. By taking advantage of the longer lifetimes of hadrons with heavy flavor (D and B mesons, for example), we can preferentially select jets containing heavy flavor for further study. I will show results from simulated data of the predicted VTX capabilities for tagging jets containing heavy flavor. The status of performing such measurements in p+p and Au+Au data collected in the RHIC 2011 run will be discussed. [Preview Abstract] |
Saturday, October 29, 2011 12:06PM - 12:18PM |
NG.00009: A Novel and Compact Muon Telescope Detector at STAR for Midrapidity Di-lepton Physics at RHIC Lijuan Ruan Data taken over the last decade have demonstrated that RHIC has created a hot, dense medium with partonic degrees of freedom. One of the physics goals for the next decade is to study the fundamental properties of this medium such as temperature, density profile, and color screening length via electro-magnetic probes such as di-leptons. Muons have a clear advantage over electrons due to reduced Bremsstrahlung radiation in the detector material. This is essential for separating the ground state (1S) of the Upsilon from its excited states (2S+3S) which are predicted to melt at very different temperatures. We propose a novel and compact Muon Telescope Detector (MTD) in the Solenoidal Tracker at RHIC (STAR) at mid-rapidity to measure different Upsilon states, J/psi over a broad transverse momentum range through di-muon decays to study color screening features, and muon-e correlations to distinguish heavy flavor correlations from initial lepton pair production. In this talk, we will present the physics cases for the proposed MTD. We will report the R\&D results including simulations and MTD prototype performance at STAR. [Preview Abstract] |
Saturday, October 29, 2011 12:18PM - 12:30PM |
NG.00010: The PHENIX MuTrig Local Level One Trigger Upgrade at PHENIX Joshua Perry The PHENIX detector at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory has had robust forward muon tracking and identification from the MuTracker and MuID detector systems for many years. The addition of the resistive plate chamber (RPC) detectors in the forward region as well as the upgrade of the muon tracker (MuTr) front-end electronics allows for greater rejection of both collision related and non-collision related backgrounds at the trigger level. The MuTrig Local Level One (LL1) trigger system allows for the rejection of events without high momentum muons originating from the collision; this allows for collision event selection (such has W boson production). This updated trigger system will ultimately increase the trigger rejection factor from a few hundred to over 9,000. The LL1 trigger system is a very sensitive system which requires active monitoring. This presentation focuses on commissioning of the MuTrig LL1 and the implementation and monitoring of the trigger system during its installation in 2011. [Preview Abstract] |
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