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1.
  • Adare, A., et al. (författare)
  • Nuclear modification factors of phi mesons in d plus Au, Cu plus Cu, and Au plus Au collisions at root s(NN)=200 GeV
  • 2011
  • Ingår i: Physical Review C. - Amer Physical Soc. - 0556-2813. ; 83:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the Relativistic Heavy Ion Collider has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p + p, d + Au, Cu + Cu, and Au + Au collisions at root s(NN) = 200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R-AA for Au + Au and Cu + Cu, and R-dA for d + Au collisions, studied as a function of transverse momentum (1 < p(T) < 7 GeV/c) and centrality. In central and midcentral Au + Au collisions, the R-AA of phi exhibits a suppression relative to expectations from binary scaled p + p results. The amount of suppression is smaller than that of the pi(0) and the. in the intermediate p(T) range (2-5 GeV/c), whereas, at higher p(T), the phi, pi(0), and. show similar suppression. The baryon (proton and antiproton) excess observed in central Au + Au collisions at intermediate p(T) is not observed for the phi meson despite the similar masses of the proton and the phi. This suggests that the excess is linked to the number of valence quarks in the hadron rather than its mass. The difference gradually disappears with decreasing centrality, and, for peripheral collisions, the R-AA values for both particle species are consistent with binary scaling. Cu + Cu collisions show the same yield and suppression as Au + Au collisions for the same number of N-part. The R-dA of phi shows no evidence for cold nuclear effects within uncertainties.
2.
  • Adare, A., et al. (författare)
  • Photon-hadron jet correlations in p plus p and Au plus Au collisions at s(NN)=200 GeV
  • 2009
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 80:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the observation at the Relativistic Heavy Ion Collider of suppression of back-to-back correlations in the direct photon+jet channel in Au+Au relative to p+p collisions. Two-particle correlations of direct photon triggers with associated hadrons are obtained by statistical subtraction of the decay photon-hadron (gamma-h) background. The initial momentum of the away-side parton is tightly constrained, because the parton-photon pair exactly balance in momentum at leading order in perturbative quantum chromodynamics, making such correlations a powerful probe of the in-medium parton energy loss. The away-side nuclear suppression factor, I-AA, in central Au+Au collisions, is 0.32 +/- 0.12(stat)+/- 0.09(syst) for hadrons of 3 < p(T)(h)< 5 in coincidence with photons of 5 < p(T)(gamma)< 15 GeV/c. The suppression is comparable to that observed for high-p(T) single hadrons and dihadrons. The direct photon associated yields in p+p collisions scale approximately with the momentum balance, z(T)equivalent to p(T)(h)/p(T)(gamma), as expected for a measurement of the away-side parton fragmentation function. We compare to Au+Au collisions for which the momentum balance dependence of the nuclear modification should be sensitive to the path-length dependence of parton energy loss.
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3.
  • Adare, A., et al. (författare)
  • Production of omega mesons in p plus p, d plus Au, Cu plus Cu, and Au plus Au collisions at root s(NN)=200 GeV
  • 2011
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 84:4, s. 044902
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the Relativistic Heavy Ion Collider has measured omega meson production via leptonic and hadronic decay channels in p + p, d + Au, Cu+ Cu, and Au + Au collisions at root s(NN) = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu Cu and Au + Au collisions show that. production has a suppression pattern at high transverse momentum, similar to that of pi(0) and eta in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R-AA, are consistent in Cu + Cu and Au + Au collisions at similar numbers of participant nucleons.
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4.
  • Adare, A., et al. (författare)
  • Charged hadron multiplicity fluctuations in Au plus Au and Cu plus Cu collisions from s(NN)=22.5 to 200 GeV
  • 2008
  • Ingår i: PHYSICAL REVIEW C. - AMER PHYSICAL SOC. - 0556-2813. ; 78:4
  • Tidskriftsartikel (refereegranskat)abstract
    • A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at <radical><radicand>s(NN)</radicand></radical>=62.4 and 200 GeV, and Cu+Cu collisions at <radical><radicand>s(NN)</radicand></radical>=22.5,62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. A comparison of the data with a model where hadrons are independently emitted from a number of hadron clusters suggests that the mean number of hadrons per cluster is small in heavy ion collisions.
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5.
  • Adare, A., et al. (författare)
  • Detailed measurement of the e(+)e(-) pair continuum in p plus p and Au plus Au collisions at root s(NN)=200 GeV and implications for direct photon production
  • 2010
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 81:3, s. 034911
  • Tidskriftsartikel (refereegranskat)abstract
    • PHENIX has measured the e(+)e(-) pair continuum in root s(NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e(+)e(-) yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c (c) over bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7 +/- 0.4(stat) +/- 1.5(syst) +/- 0.9(model). At low mass (m(ee) < 0.3 GeV/c(2)) and high p(T) (1 < p(T) < 5 GeV/c) an enhanced e(+)e(-) pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p(T), with inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar or equal to 300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p(T) < 1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T similar or equal to 100 MeV. Theoretical models underpredict the low-mass, low-p(T) enhancement.
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6.
  • Adare, A., et al. (författare)
  • Dihadron azimuthal correlations in Au+Au collisions at root s(NN)=200 GeV
  • 2008
  • Ingår i: PHYSICAL REVIEW C. - AMER PHYSICAL SOC. - 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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7.
  • Adare, A., et al. (författare)
  • Enhanced Production of Direct Photons in Au plus Au Collisions at root s(NN)=200 GeV and Implications for the Initial Temperature
  • 2010
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 104:13, s. 132301
  • Tidskriftsartikel (refereegranskat)abstract
    • The production of e(+)e(-) pairs for m(e+e-) < 0.3 GeV/c(2) and 1< p(T) < 5 GeV/c is measured in p + p and Au + Au collisions at root s(NN) = 200 GeV. An enhanced yield above hadronic sources is observed. Treating the excess as photon internal conversions, the invariant yield of direct photons is deduced. In central Au + Au collisions, the excess of the direct photon yield over p + p is exponential in transverse momentum, with an inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar to 300-600 MeV at times of similar to 0.6-0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at similar to 170 MeV.
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8.
  • Adare, A., et al. (författare)
  • Heavy-quark production in p plus p and energy loss and flow of heavy quarks in Au plus Au collisions at root s(NN)=200 GeV
  • 2011
  • Ingår i: Physical Review C. - Amer Physical Soc. - 0556-2813. ; 84:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Transverse momentum spectra of electrons (p(T)(e)) from semileptonic weak decays of heavy-flavor mesons in the range of 0.3 < p(T)(e) < 9.0 GeV/c have been measured at midrapidity (|y| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p + p and Au + Au collisions at root s(NN) = 200 GeV. In addition, the azimuthal anisotropy parameter v(2) has been measured for 0.3 < p(T)(e) < 5.0 GeV/c in Au + Au collisions. The substantial modification in the p(T)(e) spectra in Au + Au compared with p + p collisions as well as the nonzero v(2) indicate substantial interactions and flow of heavy quarks in traversing the produced medium. Comparisons of these observables with detailed theoretical calculations can be used to identify the nature of these interactions and to quantify their extent.
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9.
  • 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. - American Physical Society. - 0556-2813. ; 77:6, s. 064907
  • 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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10.
  • 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. - 0031-9007. ; 98:16, s. 162301
  • 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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