| 31. |
- Adare, A., et al.
(författare)
-
Onset of pi(0) Suppression Studied in Cu plus Cu Collisions at root s(NN)=22.4, 62.4, and 200 GeV
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 101:16
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Tidskriftsartikel (refereegranskat)abstract
- Neutral pion transverse momentum (p(T)) spectra at midrapidity (|y| less than or similar to 0.35) were measured in Cu + Cu collisions at root s(NN) = 22.4, 62.4, and 200 GeV. Relative to pi(0) yields in p + p collisions scaled by the number of inelastic nucleon-nucleon collisions (N-coll) the pi(0) yields for p(T) greater than or similar to 2 GeV/c in central Cu + Cu collisions are suppressed at 62.4 and 200 GeV whereas an enhancement is observed at 22.4 GeV. A comparison with a jet-quenching model suggests that final state parton energy loss dominates in central Cu + Cu collisions at 62.4 and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.
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| 32. |
- Adare, A., et al.
(författare)
-
Cross sections and double-helicity asymmetries of midrapidity inclusive charged hadrons in p plus p collisions at root s = 62.4 GeV
- 2012
-
Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:9
-
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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| 33. |
- Adare, A., et al.
(författare)
-
Spectra and ratios of identified particles in Au plus Au and d plus Au collisions at root s(NN)=200 GeV
- 2013
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:2
-
Tidskriftsartikel (refereegranskat)abstract
- The transverse momentum (p(T)) spectra and ratios of identified charged hadrons (pi(+/-), K-+/-, p, (p) over bar) produced in root s(NN) = 200 GeV Au + Au and d + Au collisions are reported in five different centrality classes for each collision species. The measurements of pions and protons are reported up to p(T) = 6 GeV/c (5 GeV/c), and the measurements of kaons are reported up to p(T) = 4 GeV/c (3.5 GeV/c) in Au + Au (d + Au) collisions. In the intermediate p(T) region, between 2 and 5 GeV/c, a significant enhancement of baryon-to-meson ratios compared to those measured in p + p collisions is observed. This enhancement is present in both Au + Au and d + Au collisions and increases as the collisions become more central. We compare a class of peripheral Au + Au collisions with a class of central d + Au collisions which have a comparable number of participating nucleons and binary nucleon-nucleon collisions. The p(T)-dependent particle ratios for these classes display a remarkable similarity, which is then discussed.
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| 34. |
- Adare, A., et al.
(författare)
-
Cross section and transverse single-spin asymmetry of eta mesons in p up arrow plus p collisions at root s=200 GeV at forward rapidity
- 2014
-
Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 90:7
-
Tidskriftsartikel (refereegranskat)abstract
- We present a measurement of the cross section and transverse single-spin asymmetry (AN) for. mesons at large pseudorapidity from root s = 200 GeV p up arrow + p collisions. The measured cross section for 0.5 < p(T) < 5.0 GeV/c and 3.0 < vertical bar eta vertical bar < 3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A(N) have been measured as a function of Feynman-x (x(F)) from 0.2 < vertical bar x(F)vertical bar < 0.7, as well as transverse momentum (p(T)) from 1.0 < p(T) < 4.5 GeV/c. The asymmetry averaged over positive x(F) is < A(N)> = 0.061 +/- 0.014. The results are consistent with prior transverse single-spin measurements of forward eta and pi(0) mesons at various energies in overlapping x(F) ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p up arrow + p collisions.
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| 35. |
- Adare, A., et al.
(författare)
-
Direct photon production in p plus p collisions at root s=200 GeV at midrapidity
- 2012
-
Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:7
-
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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| 36. |
- Adare, A., et al.
(författare)
-
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
-
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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| 37. |
- 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 (Nuclear Physics). - 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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| 38. |
- Adare, A., et al.
(författare)
-
Inclusive cross section and double helicity asymmetry for pi(0) production in p plus p collisions at root s=62.4 GeV
- 2009
-
Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 79:1
-
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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| 39. |
- Adare, A., et al.
(författare)
-
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
-
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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| 40. |
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