| 51. |
- Adare, A., et al.
(författare)
-
Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Central d plus Au Collisions at root s(NN)=200 GeV
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:21
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in d + Au collisions at root s(NN) = 200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central p + Pb collisions at root s(NN) = 5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in d + Au collisions at RHIC compared to those seen in p + Pb collisions at the LHC. The larger extracted upsilon(2) values in d + Au are consistent with expectations from hydrodynamic calculations owing to the larger expected initial-state eccentricity compared with that from p + Pb collisions. When both are divided by an estimate of the initial-state eccentricity the scaled anisotropies follow a common trend with multiplicity that may extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to arise from hydrodynamic flow.
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| 52. |
- Adare, A., et al.
(författare)
-
Suppression of Back-to-Back Hadron Pairs at Forward Rapidity in d plus Au Collisions at root S-NN=200 GeV
- 2011
-
Ingår i: Physical Review Letters. - 1079-7114. ; 107:17
-
Tidskriftsartikel (refereegranskat)abstract
- Back-to-back hadron pair yields in d + Au and p + p collisions at root S-NN = 200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity vertical bar eta vertical bar < 0: 35 and the associated hadron at forward rapidity (deuteron direction, 3.0< eta < 3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case, the yield of back-to-back hadron pairs in d + Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p + p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with a low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p(T), and eta points to cold nuclear matter effects arising at high parton densities.
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| 53. |
- Adare, A, et al.
(författare)
-
Azimuthal-Angle Dependence of Charged-Pion-Interferometry Measurements with Respect to Second- and Third-Order Event Planes in Au+Au Collisions at sqrt[s_{NN}]=200 GeV.
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 112:22
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Tidskriftsartikel (refereegranskat)abstract
- Charged-pion-interferometry measurements were made with respect to the second- and third-order event plane for Au+Au collisions at sqrt[s_{NN}]=200 GeV. A strong azimuthal-angle dependence of the extracted Gaussian-source radii was observed with respect to both the second- and third-order event planes. The results for the second-order dependence indicate that the initial eccentricity is reduced during the medium evolution, which is consistent with previous results. In contrast, the results for the third-order dependence indicate that the initial triangular shape is significantly reduced and potentially reversed by the end of the medium evolution, and that the third-order oscillations are largely dominated by the dynamical effects from triangular flow.
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| 54. |
- Adare, A., et al.
(författare)
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Azimuthal anisotropy of pi(0) and eta mesons in Au plus Au collisions at root s(NN)=200 GeV
- 2013
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:6
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Tidskriftsartikel (refereegranskat)abstract
- The azimuthal anisotropy coefficients v2 and v4 of p 0 and. mesons are measured in Au + Au collisions at root s(NN) = 200 GeV as a function of transverse momentum p(T) (1-14 GeV/c) and centrality. The extracted v(2) coefficients are found to be consistent between the two meson species over the measured p(T) range. The ratio of v(4)/v(2)(2) for pi(0) mesons is found to be independent of p(T) for 1- 9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with p(T). Furthermore, the ratio of v(4)/v(2)(2) is systematically larger in central collisions, which may reflect the combined effects of fluctuations in the initial collision geometry and finite viscosity in the evolving medium.
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| 55. |
- Adare, A., et al.
(författare)
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Deviation from quark number scaling of the anisotropy parameter v(2) of pions, kaons, and protons in Au+Au collisions at root s(NN)=200 GeV
- 2012
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 85:6
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the anisotropy parameter v(2) of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p(T), and transverse kinetic energy KET at midrapidity (vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(N N) = 200 GeV are presented. Pions and protons are identified up to p(T) = 6 GeV/c, and kaons up to p(T) = 4 GeV/c, by combining information from time-of-flight and aerogel Cerenkov detectors in the PHENIX Experiment. The scaling of v(2) with the number of valence quarks (n(q)) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/n(q) in noncentral Au + Au collisions (20-60%), but this scaling remains valid in central collisions (0-10%).
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| 56. |
- Adare, A., et al.
(författare)
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Gluon-Spin Contribution to the Proton Spin from the Double-Helicity Asymmetry in Inclusive pi(0) Production in Polarized p plus p Collisions at root s=200 GeV
- 2009
-
Ingår i: Physical Review Letters. - 1079-7114. ; 103:1
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Tidskriftsartikel (refereegranskat)abstract
- The double helicity asymmetry in neutral pion production for p(T) = 1 to 12 GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, Delta G, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of mu 2 = 4 GeV2 a next to leading order QCD analysis gives Delta G([0.02,0.3]) = 0.2, with a constraint of -0.7 < Delta G([0.02,0.3]) < 0.5 at Delta chi(2) = 9 (similar to 3 sigma) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the Delta G constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.
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| 57. |
- Adare, A., et al.
(författare)
-
J/psi suppression at forward rapidity in Au plus Au collisions at root s(NN)=200 GeV
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:5
-
Tidskriftsartikel (refereegranskat)abstract
- Heavy quarkonia are observed to be suppressed in relativistic heavy-ion collisions relative to their production in p + p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/psi yields at forward rapidity (1.2 < vertical bar y vertical bar < 2.2) in Au + Au collisions at root s(NN) = 200 GeV. The data confirm the earlier finding that the suppression of J/. at forward rapidity is stronger than at midrapidity, while also extending the measurement to finer bins in collision centrality and higher transverse momentum (p(T)). We compare the experimental data to the most recent theoretical calculations that incorporate a variety of physics mechanisms including gluon saturation, gluon shadowing, initial-state parton energy loss, cold nuclear matter breakup, color screening, and charm recombination. We find J/psi suppression beyond cold-nuclear-matter effects. However, the current level of disagreement between models and d + Au data precludes using these models to quantify the hot-nuclear-matter suppression.
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| 58. |
- Adare, A., et al.
(författare)
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Measurements of Higher Order Flow Harmonics in Au plus Au Collisions at root s(NN)=200 GeV
- 2011
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Ingår i: Physical Review Letters. - 1079-7114. ; 107:25
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Tidskriftsartikel (refereegranskat)abstract
- Flow coefficients nu(n) for n = 2, 3, 4, characterizing the anisotropic collective flow in Au + Au collisions at root s(NN) = 200 GeV, are measured relative to event planes Psi(n), determined at large rapidity. We report nu(n) as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order n. The nu(n) are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint can serve to improve the precision of the extracted shear viscosity to entropy density ratio eta/s.
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| 59. |
- Adare, A., et al.
(författare)
-
Neutral pion production with respect to centrality and reaction plane in Au plus Au collisions at root S-NN=200 GeV
- 2013
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 87:3
-
Tidskriftsartikel (refereegranskat)abstract
- The PHENIX experiment has measured the production of pi(0)s in Au + Au collisions at root S-NN = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p(T), to 20 GeV/c. The production ratio of eta/pi(0) is 0.46 +/- 0.01(stat) +/- 0.05(syst), constant with p(T) and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p + p and d + Au values. pi(0) are suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor R-AA vs p(T), with a slope of 0.0106 +/-(0.0034)(0.0029) (Gev/c)(-1), is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing p(T). To study the path-length dependence of suppression, the pi(0) yield is measured at different angles with respect to the event plane; a strong azimuthal dependence of the pi(0) R-AA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length L in the medium. Models based on perturbative quantum chromodynamics are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and anti-de-Sitter space/conformal field theory (AdS/CFT) for the soft interactions is consistent with the data. DOI: 10.1103/PhysRevC.87.034911
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| 60. |
- Adare, A., et al.
(författare)
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Observation of Direct-Photon Collective Flow in Au plus Au Collisions at root s(NN)=200 GeV
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:12
-
Tidskriftsartikel (refereegranskat)abstract
- The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au collisions at root s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p(T) > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with zero, which is as expected if the dominant source of direct photons is initial hard scattering. However, in the p(T) < 4 GeV/c region dominated by thermal photons, we find a substantial direct-photon v(2) comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region underpredict the observed v(2).
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