Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session PG: Ultrarelativistic Heavy Ions III |
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Chair: Julia Velkovska, Vanderbilt University Room: Peralta |
Saturday, October 31, 2015 10:30AM - 10:42AM |
PG.00001: Charm and bottom nuclear modification in Cu+Au collisions at $\sqrt{s_{NN}}$=200 GeV Cesar da Silva Forward and backward rapidity measurements in heavy ion asymmetric collisions offer the opportunity to study the nuclear modification of particle yields versus path length, time inside the medium, particle densities and different mixtures of cold nuclear matter and quark-gluon plasma effects in the same collision. The PHENIX Experiment at RHIC collected data from a large sample of Cu+Au collisions at $\sqrt{s_{NN}}$=200 GeV and, for the first time, with forward vertex detectors (FVTX) which enabled the study of displaced vertex muon decays from heavy flavor at backward and forward rapidities. Charm and bottom yields can be separated in inclusive single muon yields and bottom yield can also be obtained from J/$\psi$ vertex displacements. The status of this analysis will be presented. [Preview Abstract] |
Saturday, October 31, 2015 10:42AM - 10:54AM |
PG.00002: Time-Dependence of the Survival Probability of Quarkonia in Quark-Gluon Plasma Noor Sabrina Mah Hussin, Asmaa Shalaby, Athanasios Petridis The time-dependent Schr\"odinger equation is used to study the formation of quarkonia and their propagation in Quark-Gluon Plasma (QGP). The initial bound (ground) state is computed using imaginary-time propagation in a confining potential. The QGP is simulated with a confining potential of an extended asymptotic freedom region. The interior of the QGP potential may correspond to a vacuum that differs from that of the exterior region. The initial state propagates through this potential in real time. The survival probability is calculated versus time for various potential parameters and relative momenta of the quarkonium by projecting the interacting wavefunction onto its freely-propagating counterpart. In these calculations the staggered-leap frog method is used with special attention paid to the issue of stability. It is found that quarkonium decay is typically non-exponential. Fast moving states decay faster. Connection with experimental results is done by means of cross-section ratios. [Preview Abstract] |
Saturday, October 31, 2015 10:54AM - 11:06AM |
PG.00003: Energy dependence of $J/\psi$ production in p+p collisions at STAR Qian Yang $J/\psi$ production in heavy-ion collisions is an important tool for studying the properties of Quark-Gluon Plasma (QGP). Interpretation of these results requires a good understanding of the production mechanisms in p+p collisions, which include direct production via gluon fusion, parton fragmentation, and feed down from excited charmonium states and B hadrons. Despite decades of efforts, the $J/\psi$ production mechanism still remains a puzzle in high energy physics. $J/\psi$ measurement at a new beam energy provides new insights on $J/\psi$ production mechanism and constrains theoretical parameters. In 2013, a large fraction of the Muon Telescope Detector (MTD) was installed at mid-rapidity in STAR. This enables, for the first time, the measurement of $J/\psi$ at STAR via the di-muon channel. In this talk, we will present the measurement on $J/\psi$ production in p+p collisions at $\sqrt{s} = 200$ and 500 GeV in a wide $p_{T}$ range up to 20 GeV/c, by combing measurements from the MTD and the other detectors. We will discuss the physics perspectives of $J/\psi$ measurement in the forward pseudo-rapidity range $2.5 < \eta < 4.5$ with the proposed future Forward Calorimeter System and Forward Tracking System at STAR. [Preview Abstract] |
Saturday, October 31, 2015 11:06AM - 11:18AM |
PG.00004: Study of heavy-quark production in $p$+$p$ collisions at RHIC using different Monte-Carlo event generators Yue Hang Leung, Alan Dion, Axel Drees, Deepali Sharma Heavy flavor is one of the most sought observables to study the properties of the hot and dense medium created in heavy-ion collisions. A variety of heavy-flavor (charm and bottom) related measurements in different collision systems, as well as different collision energies have been measured at RHIC. However, the total and differential charm and bottom cross-sections are still not understood in detail. We present a comprehensive study of all the heavy flavor measurements in $p$+$p$ collisions at RHIC at $\sqrt{s_{NN}}$ = 200 GeV. We compare the measured charm and bottom $p_T$, rapidity, and correlation distributions to three different Monte-Carlo event generators, PYTHIA, MC@NLO and POWHEG. Various data sets are fitted to the spectral shapes from these event generators with the charm and bottom cross-sections as free parameters. Although the spectral shapes are well described in general, the normalization of the simulated samples are different between data sets describing different regions of phase space. These measurements suggest that while current Monte-Carlo event generators describe experimental data near mid rapidity, they are inconsistent when compared over a wide range in phase space. [Preview Abstract] |
Saturday, October 31, 2015 11:18AM - 11:30AM |
PG.00005: Study of $b\bar{b}$ angular correlations in $p+p$ collisions at $\sqrt{s} = 510$ GeV at RHIC Tristan Haseler Heavy flavor quarks are an important probe of the initial state of the Quark Gluon Plasma formed in heavy ion collisions. Understanding beauty quark production in $p+p$ collisions can give a baseline reference for studying larger collision systems. The measurement of $b\bar{b}$ angular correlations gives insight into $b$ quark production mechanisms which can directly test pQCD predictions. The $b\bar{b}$ signal can be isolated by taking advantage of the properties of $B^{0}$ oscillations in the invariant mass region of 5-10 GeV. Measuring like-sign dimuons within this mass range provides an enriched beauty signal without any contributions from quarkonia and the Drell-Yan process. $b\bar{b}$ angular correlations will be measured through the like-sign dimuon signal, in the rapidity range 1.2 $<|y|< $ 2.2 and at $\sqrt{s} = 510$ GeV from data recorded in 2013 at the PHENIX experiment. In this talk, the status of the $b\bar{b}$ angular correlations study will be presented. [Preview Abstract] |
Saturday, October 31, 2015 11:30AM - 11:42AM |
PG.00006: Multiplicity Dependence of Xi Production in pp, pPb and PbPb at CMS Hong Ni, Kong Tu, Wei Li, Julia Velkovska Identified strange and multi-strange particle production has long been considered as an important probe of thermalization and chemical equilibration of the strongly interacting system created in relativistic heavy ion collision. Recently, observations of long-range two-particle correlations in high-multiplicity pp and pPb collisions opened new opportunities for exploring QCD dynamics in small collision systems. These results pose the fundamental question of how small a system can exhibit thermalized behavior. Important parameters that could be varied in these studies are the mass of the particles, their baryon number, and their strangeness content. Multi-strange baryons provide unique probes to test baryon/meson dynamics and strangeness equilibration. The transverse momentum spectra of $\Xi^{-}$ and $\Xi^{+}$ at mid-rapidity are studied over a wide range of multiplicity in pp, pPb and PbPb systems using the CMS detector at LHC. The results are compared to the production of other strange mesons and baryons to study the baryon/meson differences and strangeness equilibration as a function of the multiplicity of final-state particles in different collision systems. [Preview Abstract] |
Saturday, October 31, 2015 11:42AM - 11:54AM |
PG.00007: $D_{s}^{\pm}$ meson production in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV in STAR Long Zhou Heavy quarks, produced in hard scattering processes in the initial stages of the collisions, are considered as excellent probes for the strongly interacting deconfined medium formed in heavy-ion collisions. The $D_{s}($c$\bar{s}/\bar{c}$s)production is affected by the strangeness enhancement and the primordial charm quark production. Thus the modification of the $D_{s}$ meson spectra in ultra-relativistic heavy-ion collisions provides a new interesting probe to the key properties of the hot nuclear medium. The Heavy Flavor Tracker, installed in STAR in 2014, has been designed to extend STAR's capability of measuring heavy flavor production by the topological reconstruction of displaced decay vertices. It provides a unique opportunity for precise measurement of the $D_{s}$ meson production. We will present the first measurement of $D_{s}$ meson production via two decay channels $D_{s}\rightarrow\phi(1020)+\pi$, and $D_{s}\rightarrow$$K+K^{\star}$(892) in Au+Au collisions at 200GeV. Preliminary results on the central-to-peripheral nuclear modification factor ($R_{cp}$) will also be presented. [Preview Abstract] |
Saturday, October 31, 2015 11:54AM - 12:06PM |
PG.00008: Nuclear Matter Effects on $\phi$ Production in Cu+Au Collisions at $\sqrt{s}_{NN}$ = 200 GeV with the PHENIX Muon Arms at RHIC Margaret Jezghani A major objective in the field of high-energy nuclear physics is to quantify and characterize the quark-gluon plasma formed in relativistic heavy-ion collisions. The $\phi$ meson is an excellent probe for studying this hot and dense state of nuclear matter due to its very short lifetime, and the absence of strong interactions between muons and the surrounding hot hadronic matter makes the $\phi$ to dimuon decay channel particularly interesting. Since the $\phi$ meson is composed of a strange and antistrange quark, its nuclear modification in heavy-ion collisions may provide insight on strangeness enhancement in-medium. Additionally, the rapidity dependence of $\phi$ production in asymmetric heavy-ion collisions provides a unique means to study the entanglement of hot and cold nuclear matter effects. In this talk, we present the measurement of $\phi$ meson production and nuclear modification in asymmetric Cu+Au heavy-ion collisions at $\sqrt{s}_{NN}$ = 200 GeV at both forward (Cu-going direction) and backward (Au-going direction) rapidities. [Preview Abstract] |
Saturday, October 31, 2015 12:06PM - 12:18PM |
PG.00009: $D^0$ Production in Au$+$Au Collisions at $\surd $sNN $=$ 200 GeV at STAR Guannan Xie The mass of charm quarks is larger than the scales of the medium created in heavy-ion collisions at RHIC energies ($m_c$$>>$$\Lambda_{QCD}$,T,$m_{u,d,s}$). This makes their production mainly feasible in the primordial nucleon-nucleon collisions, therefore, their final kinematics provide unique information on their interaction with the hot and dense medium produced in the early stages of heavy-ion collisions. Recent measurements of D0 nuclear modification factors shed light on the intricate interplay of Cold Nuclear Matter effects, hadronization mechanisms and energy loss of charm quarks in heavy-ion collisions. In this presentation, we will report D0 topological reconstruction via its golden hadronic decay channel (D0$\to$K$\pi)$ using STAR's recently installed Heavy Flavor Tracker (HFT) for reconstruction of secondary vertices. We will discuss studies of: HFT tracking efficiency from both data and simulation, D0 background reconstruction techniques, and the optimizations of D0 cuts using TMVA toolkit. The transverse-momentum and centrality dependence of D0 production in Au+Au Collisions at 200 GeV will be presented. We will also discuss nuclear modification factors and their comparison with published data from RHIC and the LHC and finally compare the results with models. [Preview Abstract] |
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