| 181. |
- Adler, S. S., et al.
(författare)
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Detailed study of high-p(T) neutral pion suppression and azimuthal anisotropy in Au plus Au collisions at root s(NN) =200 GeV
- 2007
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 76:3
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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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| 182. |
- Adler, S. S., et al.
(författare)
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Evidence for a long-range component in the pion emission source in Au plus Au collisions at root s(NN)=200 GeV
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 98:13
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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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| 183. |
- Adler, S. S., et al.
(författare)
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Measurement of single muons at forward rapidity in p+p collisions at root s=200 GeV and implications for charm production
- 2007
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-2368. ; 76:9
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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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| 184. |
- Adare, A., et al.
(författare)
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Cross sections and double-helicity asymmetries of midrapidity inclusive charged hadrons in p plus p collisions at root s = 62.4 GeV
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:9
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Tidskriftsartikel (refereegranskat)abstract
- Unpolarized cross sections and double-helicity asymmetries of single-inclusive positive and negative charged hadrons at midrapidity from p + p collisions at root s = 62.4 GeV are presented. The PHENIX measurement of the cross sections for 1.0 < p(T) < 4.5 GeV/c are consistent with perturbative QCD calculations at next-to-leading order in the strong-coupling constant, alpha(s). Resummed pQCD calculations including terms with next-to-leading-log accuracy, yielding reduced theoretical uncertainties, also agree with the data. The double-helicity asymmetry, sensitive at leading order to the gluon polarization in a momentum-fraction range of 0.05 less than or similar to x(gluon) less than or similar to 0.2, is consistent with recent global parametrizations disfavoring large gluon polarization.
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| 185. |
- Adare, A., et al.
(författare)
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Direct photon production in p plus p collisions at root s=200 GeV at midrapidity
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:7
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Tidskriftsartikel (refereegranskat)abstract
- The differential cross section for the production of direct photons in p + p collisions at root s = 200 GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider. Inclusive direct photons were measured in the transverse momentum range from 5: 5-25 GeV/c, extending the range beyond previous measurements. Event structure was studied with an isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good description of the spectrum. When the cross section is expressed versus x(T), the PHENIX data are seen to be in agreement with measurements from other experiments at different center-of-mass energies.
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| 186. |
- 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
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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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| 187. |
- Adare, A., et al.
(författare)
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Inclusive cross section and double helicity asymmetry for pi(0) production in p plus p collisions at root s=62.4 GeV
- 2009
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 79:1
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Tidskriftsartikel (refereegranskat)abstract
- The PHENIX experiment presents results from the RHIC 2006 run with polarized p + p collisions at root s = 62.4 GeV, for inclusive pi(0) production at midrapidity. Unpolarized cross section results are measured for transverse momenta p(T) = 0.5 to 7 GeV/c. Next-to-leading order perturbative quantum chromodynamics calculations are compared with the data, and while the calculations are consistent with the measurements, next-to-leading logarithmic corrections improve the agreement. Double helicity asymmetries A(LL) are presented for p(T) = 1 to 4 GeV/c and probe the higher range of Bjorken x of the gluon (x(g)) with better statistical precision than our previous measurements at root s = 200 GeV. These measurements are sensitive to the gluon polarization in the proton for 0.06 < x(g) < 0.4.
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| 188. |
- Adare, A., et al.
(författare)
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Inclusive cross section and single transverse spin asymmetry for very forward neutron production in polarized p plus p collisions at root s=200 GeV
- 2013
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 88:3
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Tidskriftsartikel (refereegranskat)abstract
- The energy dependence of the single-transverse-spin asymmetry, A(N), and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at the Relativistic Heavy Ion Collider for polarized p + p collisions at root s = 200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with a momentum fraction of x(F) = 0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x(F) scaling, compared to measurements by an experiment at the Intersecting Storage Ring, which measured neutron production in unpolarized p + p collisions at root s = 30.6-62.7 GeV. The cross sections for large x(F) neutron production for p + p collisions, as well as those in e + p collisions measured at the Hadron-Electron Ring Accelerator, are described by a pion exchange mechanism. The observed forward neutron asymmetries were large, reaching A(N) = -0.08 +/- 0.02 for x(F) = 0.8; the measured backward asymmetries, for negative x(F), were consistent with zero. The observed asymmetry for forward neutron production is discussed within the pion exchange framework, with interference between the spin-flip amplitude due to the pion exchange and nonflip amplitudes from all Reggeon exchanges. Within the pion exchange description, the measured neutron asymmetry is sensitive to the contribution of other Reggeon exchanges even for small amplitudes.
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| 189. |
- Adare, A., et al.
(författare)
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Transverse momentum dependence of J/psi polarization at midrapidity in p plus p collisions at root s=200 GeV
- 2010
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 82:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the measurement of the transverse momentum dependence of inclusive J/psi polarization in p + p collisions at root s = 200 GeV performed by the PHENIX Experiment at the Relativistic Heavy Ion Collider. The J/psi polarization is studied in the helicity, Gottfried-Jackson, and Collins-Soper frames for p(T) < 5 GeV/c and vertical bar y vertical bar < 0.35. The polarization in the helicity and Gottfried-Jackson frames is consistent with zero for all transverse momenta, with a slight (1.8 sigma) trend towards longitudinal polarization for transverse momenta above 2 GeV/c. No conclusion is allowed due to the limited acceptance in the Collins-Soper frame and the uncertainties of the current data. The results are compared to observations for other collision systems and center of mass energies and to different quarkonia production models.
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| 190. |
- Adler, SS, et al.
(författare)
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Improved measurement of double helicity asymmetry in inclulsive midrapidity pi(0) production for polarized p+p collisions at root s=200 GeV
- 2006
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 73:9
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Tidskriftsartikel (refereegranskat)abstract
- We present an improved measurement of the double helicity asymmetry for pi(0) production in polarized proton-proton scattering at root s=200 GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The improvements to our previous measurement come from two main factors: Inclusion of a new data set from the 2004 RHIC run with higher beam polarizations than the earlier run and a recalibration of the beam polarization measurements for the earlier run, which resulted in reduced uncertainties and increased beam polarizations. The results are compared to a Next to Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculation with a range of polarized gluon distributions.
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