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Sökning: WFRF:(Ozawa K.)

  • Resultat 141-150 av 220
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141.
  • Adler, S. S., et al. (författare)
  • Detailed study of high-p(T) neutral pion suppression and azimuthal anisotropy in Au plus Au collisions at root s(NN) =200 GeV
  • 2007
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 76:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of neutral pion (pi(0)) production at midrapidity in root s(NN)=200 GeV Au+Au collisions as a function of transverse momentum, p(T), collision centrality, and angle with respect to reaction plane are presented. The data represent the final pi(0) results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of 3 increase in statistics over previously published results for p(T)>6 GeV/c. We evaluate the suppression in the yield of high-p(T) pi(0)'s relative to pointlike scaling expectations using the nuclear modification factor R-AA. We present the p(T) dependence of R-AA for nine bins in collision centrality. We separately integrate R-AA over larger p(T) bins to show more precisely the centrality dependence of the high-p(T) suppression. We then evaluate the dependence of the high-p(T) suppression on the emission angle Delta phi of the pions with respect to event reaction plane for seven bins in collision centrality. We show that the yields of high-p(T) pi(0)'s vary strongly with Delta phi, consistent with prior measurements 1,2. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane, whereas the yield of pi(0)'s produced perpendicular to the reaction plane is suppressed by a factor of similar to 2. We analyze the combined centrality and Delta phi dependence of the pi(0) suppression in different p(T) bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.
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142.
  • Adler, S. S., et al. (författare)
  • Measurement of single muons at forward rapidity in p+p collisions at root s=200 GeV and implications for charm production
  • 2007
  • Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-2368. ; 76:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Muon production at forward rapidity (1.5 <=|eta|<= 1.8) has been measured by the PHENIX experiment over the transverse momentum range 1 <= p(T)<= 3 GeV/c in root s=200 GeV p+p collisions at the Relativistic Heavy Ion Collider. After statistically subtracting contributions from light hadron decays an excess remains which is attributed to the semileptonic decays of hadrons carrying heavy flavor, i.e. charm quarks or, at high p(T), bottom quarks. The resulting muon spectrum from heavy flavor decays is compared to PYTHIA and a next-to-leading-order perturbative QCD calculation. PYTHIA is used to determine the charm quark spectrum that would produce the observed muon excess. The corresponding differential cross section for charm quark production at forward rapidity is determined to be d sigma(c (c) over bar)/dy|(y=1.6)=0.243 +/- 0.013(stat.)+/- 0.105(data syst.)(-0.087)(+0.049)(PYTHIA syst.) mb.
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143.
  • Adare, A., et al. (författare)
  • Event structure and double helicity asymmetry in jet production from polarized p plus p collisions at root s=200 GeV
  • 2011
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 84:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the event structure and double helicity asymmetry (A(LL)) of jet production in longitudinally polarized p + p collisions at root s = 200 GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity vertical bar eta vertical bar < 0.35 with the requirement of a high-momentum (> 2 GeV/c) photon in the event. Event structure, such as multiplicity, p(T) density and thrust in the PHENIX acceptance, were measured and compared with the results from the PYTHIA event generator and the GEANT detector simulation. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet A(LL), photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster pT sum (p(T)(reco)). The effect of detector response and the underlying events on p(T)(reco) was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4< p(T)(reco) < 12 GeV/c with an average beam polarization of < P > = 49% we measured Lambda(LL) = -0.0014 +/- 0.0037(stat) at the lowest p(T)(reco) bin (4-5 GeV= c) and -0.0181 +/- 0.0282(stat) at the highest p(T)(reco) bin (10-12 GeV= c) with a beam polarization scale error of 9.4% and a pT scale error of 10%. Jets in the measured p(T)(reco) range arise primarily from hard-scattered gluons with momentum fraction 0: 02 < x < 0: 3 according to PYTHIA. The measured A(LL) is compared with predictions that assume various Delta G(x) distributions based on the Gluck-Reya-Stratmann-Vogelsang parameterization. The present result imposes the limit -a.1 < integral(0.3)(0.02) dx Delta G(x, mu(2) = GeV2) < 0.4 at 95% confidence level or integral(0.3)(0.002) dx Delta G(x, mu(2) = 1 GeV2) < 0.5 at 99% confidence level.
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144.
  • Adare, A., et al. (författare)
  • J/psi production in root s(NN)=200 GeV Cu+Cu collisions
  • 2008
  • Ingår i: Physical Review Letters. - 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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145.
  • 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. - 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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146.
  • 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. - 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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147.
  • Adare, A., et al. (författare)
  • Nuclear-modification factor for open-heavy-flavor production at forward rapidity in Cu plus Cu collisions at root s(NN)=200 GeV
  • 2012
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 86:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Heavy-flavor production in p + p collisions is a good test of perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p + p results, quantified with the nuclear-modification factor (R-AA), provides information on both cold-and hot-nuclear-matter effects. Midrapidity heavy-flavor R-AA measurements at the Relativistic Heavy Ion Collider have challenged parton-energy-loss models and resulted in upper limits on the viscosity-entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region. Purpose: Determine transverse-momentum (p(T)) spectra and the corresponding R-AA for muons from heavy-flavor meson decay in p + p and Cu + Cu collisions at root s(NN) = 200 GeV and y = 1.65. Method: Results are obtained using the semileptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the p(T) spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p + p collisions at root s = 200 GeV, integrated over p(T) and in the rapidity range 1.4 < y < 1.9, is found to be d(sigma e (e) over bar)/dy = 0.139 +/- 0.029 (stat)(-0.058)(+0.051) (syst) mb. This result is consistent with a perturbative fixed-order-plus-next-to-leading-log calculation within scale uncertainties and is also consistent with expectations based on the corresponding midrapidity charm-production cross section measured by PHENIX. The R-AA for heavy-flavor muons in Cu + Cu collisions is measured in three centrality bins for 1 < p(T) < 4 GeV/c. Suppression relative to binary-collision scaling (R-AA < 1) increases with centrality. Conclusions: Within experimental and theoretical uncertainties, the measured charm yield in p + p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu + Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.
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148.
  • Adare, A., et al. (författare)
  • System-size dependence of open-heavy-flavor production in nucleus-nucleus collisions at root s(NN)=200 GeV
  • 2014
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open-heavy-flavor production in Cu + Cu collisions at v root s(NN) = 200 GeV through the measurement of electrons at midrapidity that originate from semileptonic decays of charm and bottom hadrons. In peripheral Cu + Cu collisions an enhanced production of electrons is observed relative to p + p collisions scaled by the number of binary collisions. In the transverse momentum range from 1 to 5 GeV/c the nuclear modification factor is R-AA similar to 1.4. As the system size increases to more central Cu + Cu collisions, the enhancement gradually disappears and turns into a suppression. For p(T) > 3 GeV/c, the suppression reaches R-AA similar to 0.8 in the most central collisions. The p(T) and centrality dependence of R-AA in Cu + Cu collisions agree quantitatively with R-AA in d + Au and Au + Au collisions, if compared at a similar number of participating nucleons < N-part >.
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149.
  • Adler, S. S., et al. (författare)
  • Dense-medium modifications to jet-induced hadron pair distributions in Au+Au collisions at root(NN)-N-S=200 GeV
  • 2006
  • Ingår i: Physical Review Letters. - 1079-7114. ; 97:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at root s(NN)=200 GeV. The distribution of jet-associated partner hadrons (1.0 < p(T)< 2.5 GeV/c) per trigger hadron (2.5 < p(T)< 4.0 GeV/c) is found to vary with collision centrality, in both shape and yield, indicating a significant effect of the nuclear collision medium on the jet fragmentation process.
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150.
  • Adler, S. S., et al. (författare)
  • Evidence for a long-range component in the pion emission source in Au plus Au collisions at root s(NN)=200 GeV
  • 2007
  • Ingår i: Physical Review Letters. - 1079-7114. ; 98:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in Au+Au collisions at s(NN)=200 GeV. The source parameters extracted from these functions at low k(T) give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.
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  • Resultat 141-150 av 220

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