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Träfflista för sökning "WFRF:(Chang Hong) ;srt2:(2005-2009)"

Sökning: WFRF:(Chang Hong) > (2005-2009)

  • Resultat 11-20 av 48
  • Föregående 1[2]345Nästa
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11.
  • Adare, A., et al. (författare)
  • Dihadron azimuthal correlations in Au+Au collisions at root s(NN)=200 GeV
  • 2008
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 78:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Azimuthal angle (Delta phi) correlations are presented for a broad range of transverse momentum (0.4 < p(T) < 10 GeV/c) and centrality (0-92%) selections for charged hadrons from dijets in Au+Au collisions at root s(NN) = 200 GeV. With increasing p(T), the away-side Delta phi distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons with p + p data suggest that the away-side distribution can be divided into a partially suppressed "head" region centered at Delta phi similar to pi, and an enhanced "shoulder" region centered at Delta phi similar to pi +/- 1.1. The p(T) spectrum for the associated hadrons in the head region softens toward central collisions. The spectral slope for the shoulder region is independent of centrality and trigger p(T). The properties of the near-side distributions are also modified relative to those in p + p collisions, reflected by the broadening of the jet shape in Delta phi and Delta eta, and an enhancement of the per-trigger yield. However, these modifications seem to be limited to p(T)less than or similar to 4 GeV/c, above which both the hadron pair shape and per-trigger yield become similar to p + p collisions. These observations suggest that both the away- and near-side distributions contain a jet fragmentation component which dominates for p(T) greater than or similar to 5 GeV/c and a medium-induced component which is important for p(T) less than or similar to 4 GeV/c. We also quantify the role of jets at intermediate and low p(T) through the yield of jet-induced pairs in comparison with binary scaled p + p pair yield. The yield of jet-induced pairs is suppressed at high pair proxy energy (sum of the p(T) magnitudes of the two hadrons) and is enhanced at low pair proxy energy. The former is consistent with jet quenching; the latter is consistent with the enhancement of soft hadron pairs due to transport of lost energy to lower p(T).
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12.
  • Adare, A., et al. (författare)
  • Dilepton mass spectra in p plus p collisions at root s=200 GeV
  • 2009
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 670:4-5, s. 313-320
  • Tidskriftsartikel (refereegranskat)abstract
    • PHENIX has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c(2) in p + p collisions at root s = 200 GeV. The contributions from light meson decays to e(+)e(-) pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of similar to 20% they account for all e(+)e(-) pairs in the mass region below similar to 1 GeV/c(2). The e(+)e(-) pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) pb. which is consistent with QCD calculations and measurements of single leptons by PHENIX. (C) 2008 Elsevier BV. All rights reserved.
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13.
  • Adare, A., et al. (författare)
  • Energy loss and flow of heavy quarks in Au+Au collisions at root s(NN) = 200 GeV
  • 2007
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 98:17
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured electrons with 0.3 < p(T) < 9 GeV/c at midrapidity (y < 0.35) from heavy-flavor (charm and bottom) decays in Au + Au collisions at root s(NN) = 200 GeV. The nuclear modification factor R-AA relative to p + p collisions shows a strong suppression in central Au + Au collisions, indicating substantial energy loss of heavy quarks in the medium produced at RHIC energies. A large azimuthal anisotropy v(2) with respect to the reaction plane is observed for 0.5 < p(T) < 5 GeV/c indicating substantial heavy-flavor elliptic flow. Both R-AA and v(2) show a p(T) dependence different from those of neutral pions. A comparison to transport models which simultaneously describe R-AA(p(T)) and v(2)(p(T)) suggests that the viscosity to entropy density ratio is close to the conjectured quantum lower bound, i.e., near a perfect fluid.
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14.
  • Adare, A., et al. (författare)
  • J/psi production in root s(NN)=200 GeV Cu+Cu collisions
  • 2008
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 101:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Yields for J/psi production in Cu+Cu collisions at root s(NN) = 200 GeV have been measured over the rapidity range |y|< 2.2 and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data offer greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, in the range where the quark-gluon plasma transition threshold is predicted to lie. Cold nuclear matter estimates based on ad hoc fits to d+Au data describe the Cu+Cu data up to N-part similar to 50, corresponding to a Bjorken energy density of at least 1.5 GeV/fm(3).
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15.
  • Adare, A., et al. (författare)
  • J/psi production versus centrality, transverse momentum, and rapidity in Au+Au collisions at root S(NN) = 200 GeV
  • 2007
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 98:23
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2 < y < 2.2 in Au+Au collisions at root s(NN)=200 GeV. The J/psi invariant yield and nuclear modification factor R-AA as a function of centrality, transverse momentum, and rapidity are reported. A suppression of J/psi relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy J/psi data at the CERN Super Proton Synchrotron invoking only J/psi destruction based on the local medium density predict a significantly larger suppression at RHIC and more suppression at midrapidity than at forward rapidity. Both trends are contradicted by our data.
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16.
  • Adare, A., et al. (författare)
  • J/psi production versus transverse momentum and rapidity in p+p collisions at root s=200 GeV
  • 2007
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 98:23
  • Tidskriftsartikel (refereegranskat)abstract
    • J/psi production in p+p collisions at root s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over a rapidity range of -2.2 < y < 2.2 and a transverse momentum range of 0 < p(T)< 9 GeV/c. The size of the present data set allows a detailed measurement of both the p(T) and the rapidity distributions and is sufficient to constrain production models. The total cross section times the branching ratio is B-ll sigma(J/psi)(pp)=178 +/- 3(stat)+/- 53(sys)+/- 18(norm) nb.
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17.
  • Adare, A., et al. (författare)
  • Measurement of High-p(T) single electrons from heavy-flavor decays in p+p collisions at root s=200 GeV
  • 2006
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 97:25
  • Tidskriftsartikel (refereegranskat)abstract
    • The momentum distribution of electrons from decays of heavy flavor (charm and bottom) for midrapidity |y|< 0.35 in p+p collisions at s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.3 < p(T)< 9 GeV/c. Two independent methods have been used to determine the heavy-flavor yields, and the results are in good agreement with each other. A fixed-order-plus-next-to-leading-log perturbative QCD calculation agrees with the data within the theoretical and experimental uncertainties, with the data/theory ratio of 1.71 +/- 0.02(stat)+/- 0.18(sys) for 0.3 < p(T)< 9 GeV/c. The total charm production cross section at this energy has also been deduced to be sigma(cc)=567 +/- 57(stat)+/- 193(sys) mu b.
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18.
  • Adare, A., et al. (författare)
  • Quantitative constraints on the transport properties of hot partonic matter from semi-inclusive single high transverse momentum pion suppression in Au plus Au collisions at root S-NN=200 GeV
  • 2008
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 77:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum pi(0)'s in Au+Au collisions at root s(NN) = 200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN(g)/dy, the medium transport coefficient <(q) over cap >, or the initial energy-loss parameter epsilon(0). We find that high-transverse-momentum pi(0) suppression in Au+Au collisions has sufficient precision to constrain these model-dependent parameters at the +/- 20-25% (one standard deviation) level. These constraints include only the experimental uncertainties, and further studies are needed to compute the corresponding theoretical uncertainties.
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19.
  • Adare, A., et al. (författare)
  • Scaling properties of azimuthal anisotropy in Au plus Au and Cu plus Cu collisions at root s(NN)=200 GeV
  • 2007
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 98:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Differential measurements of elliptic flow (v(2)) for Au+Au and Cu+Cu collisions at root s(NN)=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v(2) with eccentricity, system size, and transverse kinetic energy (KET). For KET equivalent to m(T)-m up to similar to 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KET mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v(2) for both mesons and baryons over the full KET range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KET, rather than transverse momentum.
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20.
  • Adare, A., et al. (författare)
  • Suppression Pattern of Neutral Pions at High Transverse Momentum in Au plus Au Collisions at root S-NN=200 GeV and Constraints on Medium Transport Coefficients
  • 2008
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 101:23
  • Tidskriftsartikel (refereegranskat)abstract
    • For Au + Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, p(T), up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 < p(T) < 20 GeV/c. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e. g., <(q) over cap > in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au + Au collisions.
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  • Resultat 11-20 av 48
  • Föregående 1[2]345Nästa
 
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