Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session FJ: Ultrarelativistic Heavy Ions - Experiment |
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Chair: Ali Hanks, Stony Brook University Room: Queen's 5 |
Friday, October 10, 2014 9:00AM - 9:15AM |
FJ.00001: Studying the Phase Diagram on QCD Matter at RHIC Daniel Cebra In first phase of the Beam Energy Scan program at RHIC (BES-I), collisions energies of 200, 62.4, 39.0, 27.0, 19.6, 14.5, 11.5, and 7.7 GeV were studied. This program has allowed access to a region of the QCD phase diagram which statistical hadronization models suggest covers a range of baryon chemical potential ($\mu_B$) from 20 to 420 MeV. Some, but nor all, lattice QCD models suggest that interesting features of the phase diagram (i.e. the possible first-order phase transition and a possible critical point) may be accessible in this search region. Several analyses of BES-I data have further explored lines of analysis that have been used to support the claim of quark-gluon plasma (QGP) discovery at the top RHIC energy $\sqrt{s_{NN}}$ = 200 GeV. Results and conclusions from the BES-I program will be reviewed. Upgrades to the collider and to the STAR detector in the next few years will enable a second phase of the Beam Energy Scan (BES Phase-II) at RHIC in 2018 and 2019. These upgrades and the physics analyses which they make possible will be presented. [Preview Abstract] |
Friday, October 10, 2014 9:15AM - 9:30AM |
FJ.00002: ABSTRACT WITHDRAWN |
Friday, October 10, 2014 9:30AM - 9:45AM |
FJ.00003: $J/\psi$ production as a function of charged particle multiplicity in $p+p$ collisions at $\sqrt{s} = 510$ GeV Haiwang Yu In a high energy proton-proton collision, more than one inelastic parton-parton interaction can occur, which is described as multiple parton interaction (MPI). Each of the parton interaction would contribute to the overall particle multiplicity, as well as higher probability of producing a $J/\psi$ particle in the collision. Therefore, the MPI scenario can be tested by studying the yield of $J/\psi$ as a function of multiplicity. In addition, such measurement also provides additional information on the $J/\psi$ production mechanism, which is still not fully understood. During the 2013 RHIC run, the PHENIX experiment collected high statistics proton-proton collision data at $\sqrt{s} = 510$ GeV. Using the PHENIX muon spectrometers covering $1.2 < |\eta| < 2.4$, $J/\psi$ particles are identified by detecting the decayed $\mu^+ \mu^-$ pairs. The $J/\psi$ yield was studied against the charged particle multiplicity, measured by the recently installed forward silicon detectors. In this talk, the latest status of this analysis will be presented. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FJ.00004: J/$\psi $ photo-production measurement at RHIC using the STAR detector for $\surd $s$_{\mathrm{NN}} = $ 200 GeV Au$+$Au collisions Chanaka De Silva Ultra-peripheral collision events are effectively photo-production on nuclear targets. Relativistic heavy ions carry strong transverse electromagnetic fields that can be treated as sources of quasi-real virtual photons. The ions interact through photon-Pomeron and photon-photon collisions at impact parameters more than twice the nuclear radius, so hadronic interactions are suppressed in ultra-peripheral events. These events also provide an ideal proving ground for new programs in e$+$A physics. We present the latest results on J/$\psi $ photo-production using $\surd $s$_{\mathrm{NN}} = $ 200 GeV Au$+$Au collisions in the STAR experiment at RHIC. The p$_{\mathrm{T}}$ distribution of the J/$\psi $ mesons peaks at very low p$_{\mathrm{T}}$, consistent with expectations for coherent photo-production. We further discuss the current status of measurements that are expected to provide information on nuclear gluon distributions, gluon shadowing, generalized parton distributions and parton form factors. Finally, we present the measurement of the ratio of J/$\psi $ to $\rho $ production as a function of rapidity for $\surd $s$_{\mathrm{NN}} = $ 200 GeV Au$+$Au collisions. Possible theory comparisons are also discussed. [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FJ.00005: Balance Functions from Au+Au Collisions at $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV Gary Westfall We present balance functions from Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV measured at STAR and compare with recent results for Pb+Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV [1]. We find that the balance function narrows as the collisions become more central and as the incident energy increases, which is consistent with the concept of delayed hadronization of a deconfined quark-gluon plasma (QGP). We also present balance functions for $\pi^{+}\pi^{-}$ pairs, $K^{+}K^{-}$ pairs, $p\bar{p}$ pairs, and $pK^{-}$ pairs from central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. We compare to a model [2] that relates these balance functions to the correlations of up, down, and strange quarks in the QGP created in central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. Our results are consistent with two waves of charge creation in time, one early in the collision ($\sim 1$ fm/$c$) and a second at hadronization ($\sim 5-10$ fm/$c$). We find that the densities of up, down, and strange quarks in the QGP extracted from the model comparison are consistent with current lattice gauge calculations.\\[4pt] [1] ALICE, Phys. Lett. B 723, 267 (2013).\\[0pt] [2] S. Pratt, Phys. Rev. Lett. 108, 212301 (2012); S. Pratt, Phys. Rev. C 85, 014904 (2012); S. Pratt, PoS(CPOD 2013)023. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FJ.00006: Energy Dependence of the Width of the Pion Rapidity Density Distribution from STAR Christopher Flores By analyzing events with longitudinally displaced vertices the STAR Collaboration will measure the width of the rapidity-density distribution of negatively charged pions. The ratio of the measured width to the width predicted by Landau hydrodynamics is interpreted analogously to the speed of sound and has previously been seen to exhibit a minimum as a function of center-of-mass energy [1]. Because the speed of sound is sensitive to the bulk properties of the medium through which it propagates, finding non-monotonic behavior in this ratio as a function of center-of-mass energy is suggestive of a change in the equation of state of the medium. The data used in this analysis cover center-of-mass energies of $\sqrt{s_{NN}} = 3.0, 3.5, 4.5, 11. 5$ and $19.6$ GeV. The lowest three energies were obtained from fixed-target interactions between heavy beam-halo nuclei and the aluminum vacuum pipe, while the remaining energies were obtained from Au+Au collider events. Here, we discuss the performance of the STAR detector for measuring these types of events, the methodology utilized in the analysis, and the measured dependence of the width of the pion rapidity-density distribution as a function of center-of-mass energy.\\[4pt] [1] H. Peterson, M. Bleicher, Proc. of Science arXiv:nucl-th/0611001 [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FJ.00007: Measurements of di-electron production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV by RHIC-PHENIX using Hadron Blind Detector Yosuke Watanabe Di-electron measurement is a powerful tool to diagnose the strongly interacting matter created in high-energy heavy ion collisions. Since electrons are not subject to final state interactions, they carry the information at the time of their production. In particular, low mass di-electron measurement allows us to study chiral symmetry restoration and possible medium modifications of the low mass vector mesons, such as $\rho$, $\omega$ and $\phi$. In an earlier di-electron measurement by PHENIX, a large enhancement of a factor of $\sim$5 with respect to expected hadronic sources was observed in the low mass region 0.15-0.75 GeV/$c^2$ for minimum bias events. However, the previous measurement suffer from a large number of background electrons originating from $\pi^0$ Dalitz decays and $\gamma$ conversions. A new detector, Hadron Blind Detector (HBD), is developed to reject those background electrons by exploiting the fact that the opening angle of such pairs is very small compared to the opening angle of other sources like the light vector mesons. In 2009 and 2010, the HBD was successfully operated and a data sample of p+p collisions and Au+Au collisions were collected. The current status of the di-electron analysis at RHIC-PHENIX is presented. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FJ.00008: The Study of Two Anti-Proton Interaction via Correlation Measurement at STAR Zhengqiao Zhang Two-particle correlations at small relative momenta are influenced by the nuclear force between the two particles, which has been intensively studied for nucleons and nuclei but not much for anti-nucleons or anti-nuclei. The study of the force between (anti)nucleons is a necessary step to understand the structure of (anti)nuclei and how (anti)nuclei interact with each other. In this presentation, by studying the two anti-proton correlation function in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 {\rm GeV} collected by the STAR experiment at RHIC, we show the attracting nuclear force between two anti-protons. We also present the measurement of the two key parameters that characterize the corresponding strong interaction, namely, the scattering length and the effective range. As a direct knowledge of the interaction between two anti-protons, the simplest system of anti-nucleons (nuclei), our result provides a fundamental ingredient for understanding the structure of more sophisticated anti-nuclei and their properties. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FJ.00009: Transverse Energy Distributions Measured in the RHIC Beam Energy Scan Using the PHENIX Muon Piston Calorimeter Brett Fadem Most RHIC beam energy scan results have been obtained at midrapidity. Using the PHENIX Muon Piston Calorimeter, which covers a pseudorapidity range of $3.1<|\eta|<3.8$, measurement of transverse energy distributions can be extended to forward/backword rapidities which are associated with larger values of baryon chemical potential and represent a different region of the phase diagram. In this talk, we present the latest PHENIX results for this observable in Au+Au collisions at $\sqrt{s_{NN}}=$200, 62.4, 39, and 7.7~GeV. [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FJ.00010: An iPython-based Monte-Carlo Glauber Model of Nuclear Collisions Jennifer Klay, Chad Rexrode, Kathryn Tzekov An iPython-based package to simulate the Monte-Carlo Glauber model of nuclear interactions was developed and published online for broad distribution. The simulation utilizes compiled data on nuclear charge density distributions to create nuclei and cross-section data from the Particle Data Group to generate large statistics simulations across a broad range of energies and collision systems. The simulation correlates the number of nucleons participating in a collision as well as the number of binary collisions with the impact parameter for each event. Individual collisions can be visually represented, demonstrating the event-by-event variation of particular geometric overlaps, which are obscured in the ensemble data. Good agreement between the program and expected results for Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV is demonstrated. Examples of possible future RHIC experiments such as He$^3$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV will be shown. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FJ.00011: Study of direct photon asymmetry via dielectron pairs at RHIC-PHENIX Tomoya Hoshino Creation of a strong magnetic field in non-central heavy ion collisions is predicted by several theoretical models. The field can reach as high as $10^{14}$ teslas at RHIC. Theoretical calculation using vacuum polarization tensor in an external strong magnetic field predicts an asymmetry of virtual photon decays with respect to the reaction plane [1]. In addition, polarization of direct (virtual) photons via gluon-quark Compton scattering was predicted by [2]. These two phenomena may cause an asymmetry of the decay angle of dielectron pairs with respect to the reaction plane. The PHENIX experiment has excellent electron identification capabilities and can be used for search of such asymmetry. We report current status of the analysis aiming on the measurement of dielectron pair asymmetry and discuss experimental challenges to measure asymmetry of direct virtual photons. \\[4pt] [1] K. Ishikawa et. al., Int. J. Mod. Phys. A28, 1350100 (2013)\\[0pt] [2] G. Baym and T. Hatsuda, arXiv:1405.1376 [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FJ.00012: Measurement of $\pi^{0}$ mesons in p-Pb collisions at $\surd $s$_{\mathrm{NN}} = $ 5.02 TeV with PHOS in ALICE at LHC Tsubasa Okubo Suppression of high p$_{\mathrm{T}}$ charged particles has been observed in heavy-ion collisions at LHC energies, however the suppression mechanism has not been understood yet. Studies of particle production in p-A collisions provide us new information whether the suppression is originated from an initial condition of colliding nuclei or due to the final effects in quark matter created by the collision. We have measured neutral pions emitted in p-Pb collisions at $\surd $s$_{\mathrm{NN}} = $ 5.02 TeV with PHOS at the ALICE experiment. The PHOS is a unique and precise photon spectrometer composed of lead tungstate crystals. With its outstanding performances of precise-granularity and high energy resolution, neutral pions can be identified via two photon decays at an excellent mass resolution $\delta $m/m $=$ 3{\%}. Raw yields of pions out of a 90 million minimum-bias event sample were counted in invariant mass spectra. The raw yields were corrected for reconstruction efficiencies and acceptances with Monte-Carlo analyses. We will discuss the corrected p$_{\mathrm{T}}$ spectrum up to 20 GeV/c. [Preview Abstract] |
Friday, October 10, 2014 12:00PM - 12:15PM |
FJ.00013: Azimuthal quadrupole correlation from gluon interference in 200 GeV p+p collisions Robert Ray The BFKL multi-Pomeron model of Levin and Rezaeian [1], with extension to the gluon saturation region, is applied to long-range pseudorapidity correlations on relative azimuth for intermediate momentum (few GeV/$c$) final-state hadrons produced in $\sqrt{s}$ = 200~GeV p+p collisions [2]. The multi-Pomeron exchange probabilities in the model were estimated by fitting the minimum-bias p+p multiplicity frequency distribution. The multi-Pomeron model prediction for the amplitude of the minimum-bias average quadrupole correlation, proportional to $\cos 2(\phi_1 - \phi_2)$, is consistent with preliminary measurements from STAR [3]. The gluon saturation momentum scale required by the model to describe the measured multiplicity dependence of the quadrupole correlation is also consistent with theoretical expectations for the saturation scale. The results presented here support a multiple parton-shower, gluon interference mechanism for generating the long-range pseudorapidity, azimuthal quadrupole correlation observed in high-energy p+p collisions.\\[4pt] [1] E. Levin and A. Rezaeian, Phys. Rev. D {\bf 84}, 034031 (2011);\\[0pt] [2] Ray, arXiv:1406.2736;\\[0pt] [3] D. Prindle, T. Trainor (STAR Collaboration), arXiv:1310.0408v1. [Preview Abstract] |
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