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1.
  • 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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2.
  • Adare, A., et al. (författare)
  • Direct photon production in d+Au collisions at root s(NN)=200 GeV
  • 2013
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 87:5, s. 054907
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct photons have been measured in root s(NN) = 200 GeV d + Au collisions at midrapidity. A wide p(T) range is covered by measurements of nearly real virtual photons (1 < p(T) < 6 GeV/c) and real photons (5 < p(T) < 16 GeV/c). The invariant yield of the direct photons in d + Au collisions over the scaled p + p cross section is consistent with unity. Theoretical calculations assuming standard cold-nuclear-matter effects describe the data well for the entire p(T) range. This indicates that the large enhancement of direct photons observed in Au + Au collisions for 1.0 < p(T) < 2.5 GeV/c is attributable to a source other than the initial-state nuclear effects.
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3.
  • 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.
4.
  • 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. - Amer Physical Soc. - 1550-7998. ; 90:7, s. 072008
  • 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.
5.
  • Adare, A., et al. (författare)
  • Cold Nuclear Matter Effects on J/psi Yields as a Function of Rapidity and Nuclear Geometry in d plus A Collisions at root S-NN=200 GeV
  • 2011
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 107:14, s. 142301
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of J/psi yields in d + Au collisions at root S-NN = 200 GeV recorded by the PHENIX experiment and compare them with yields in p + p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/psi rapidity (-2.2 < y < 2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. In order to remove model dependent systematic uncertainties we also compare the data to a simple geometric model. The forward rapidity data are inconsistent with nuclear modifications that are linear or exponential in the density weighted longitudinal thickness, such as those from the final state breakup of the bound state.
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6.
  • Adare, A., et al. (författare)
  • Ground and excited state charmonium production in p plus p collisions at root s=200 GeV
  • 2012
  • Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 85:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on charmonium measurements J/psi (1S), psi' (2S), and chi(c) (1P) in p + p collisions at root s = 200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi(c) in the midrapidity region (vertical bar y vertical bar < 0: 35) is 9.6 +/- 2.4% and 32 +/- 9%, respectively. We also present the p(T) and rapidity dependencies of the J/psi yield measured via dielectron decay at midrapidity (vertical bar y vertical bar < 0.35) and via dimuon decay at forward rapidity (1.2 < vertical bar y vertical bar < 2.2). The statistical precision greatly exceeds that reported in our previous publication Phys. Rev. Lett. 98, 232002 (2007). The new results are compared with other experiments and discussed in the context of current charmonium production models.
7.
  • Adare, A., et al. (författare)
  • Heavy-flavor electron-muon correlations in p plus p and d plus Au collisions at root s(NN)=200 GeV
  • 2014
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 89:3, s. 034915
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Heavy-flavor modification in relativistic p(d) + A collisions are sensitive to different kinds of strong-interaction physics ranging from modifications of the nuclear wave function to initial- and final-state energy loss. Modifications to single heavy-flavor particles and their decay leptons at midrapidity and forward rapidity are well established at the Relativistic Heavy Ion Collider (RHIC). Purpose: This paper presents measurements of azimuthal correlations of electron-muon pairs produced from heavy-flavor decays, primarily c (c) over bar, in root s(NN) = 200 GeV p + p and d + Au collision using the PHENIX detector at RHIC. The electrons are measured at midrapidity while the muons in the pair are measured at forward rapidity, defined as the direction of the deuteron beam, in order to utilize the deuteron to probe low-x partons in the gold nucleus. Methods: This analysis uses the central spectrometer arms for electron identification and forward spectrometer arms for muon identification. Azimuthal correlations are built in all sign combinations for e-mu pairs. Subtracting the like-sign yield from the unlike-sign yield removes the correlations from light flavor decays and conversions. Results: Comparing the p + p results with several different Monte Carlo event generators, we find the results are consistent with a total charm cross section sigma(c (c) over bar) = 538 +/- 46 (stat) +/- 197 (data syst) +/- 174 (model syst) mu b. These generators also indicate that the back-to-back peak at Delta phi = pi is dominantly from the leading-order contributions (gluon fusion), while higher-order processes (flavor excitation and gluon splitting) contribute to the yield at all Delta phi. We observe a suppression in the pair yield per collision in d + Au. We find the pair yield suppression factor for 2.7 < Delta phi < 3.2 rad is J(dA) = 0.433 +/- 0.087 (stat) +/- 0.135 (syst). Conclusions: The e-mu pairs result from partons at x(Au) similar to 10(-2) at Q(2) = 10 GeV/c(2) at the edge of the shadowing region. The pair suppression indicates modification to c (c) over bar pairs for these kinematics in the cold nuclear medium at RHIC.
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8.
  • Adare, A., et al. (författare)
  • Measurement of K-S(0) and K*(0) in p plus p, d plus Au, and Cu plus Cu collisions at root s(NN)=200 GeV
  • 2014
  • Ingår i: Physical Review C. - Amer Physical Soc. - 0556-2813. ; 90:5, s. 054905
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K-S(0) and K*(0) meson production at midrapidity in p + p, d + Au, and Cu + Cu collisions at root s(NN) = 200 GeV. The K-S(0) and K*(0) mesons are reconstructed via their K-S(0) -> pi(0)(-> gamma gamma) pi(0)(-> gamma gamma) and K*(0) -> K-+/-pi(-/+) decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K-S(0) and K*(0) mesons in d + Au and Cu + Cu collisions at different centralities. In the d + Au collisions, the nuclear modification factor of K-S(0) and K*(0) mesons is almost constant as a function of transverse momentum and is consistent with unity, showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu + Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the p + p yield scaled by the number of binary nucleon-nucleon collisions in the Cu + Cu system. In the p(T) range 2-5 GeV/c, the strange mesons (K-S(0), K*(0)) similarly to the phi meson with hidden strangeness, showan intermediate suppression between the more suppressed light quark mesons (pi(0)) and the nonsuppressed baryons (p, (p) over bar). At higher transverse momentum, p(T) > 5 GeV/c, production of all particles is similarly suppressed by a factor of approximate to 2.
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9.
  • Adare, A., et al. (författare)
  • Measurement of transverse single-spin asymmetries for J/psi production in polarized p plus p collisions at root s=200 GeV
  • 2010
  • Ingår i: Physical Review D. - Amer Physical Soc. - 1550-7998. ; 82:11
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the first measurement of transverse single-spin asymmetries in J/psi production from transversely polarized p + p collisions at root s = 200 GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges 1.2 < vertical bar y vertical bar < 2.2 and vertical bar y vertical bar < 0.35 for transverse momenta up to 6 GeV/c. J/psi production at the Relativistic Heavy Ion Collider is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the J/psi can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the J/psi production mechanism. Asymmetries were obtained as a function of J/psi transverse momentum and Feynman-x, with a value of -0.086 +/- 0.026(stat) +/- 0.003(syst) in the forward region. This result suggests possible nonzero trigluon correlation functions in transversely polarized protons and, if well defined in this reaction, a nonzero gluon Sivers distribution function.
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10.
  • Adare, A., et al. (författare)
  • Search for dark photons from neutral meson decays in p plus p and d plus Au collisions at root s(NN)=200 GeV
  • 2015
  • Ingår i: Physical Review C. - Amer Physical Soc. - 0556-2813. ; 91:3, s. 031901
  • Tidskriftsartikel (refereegranskat)abstract
    • The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g - 2)mu deviates from SM calculations by 3.6 sigma. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in pi(0), eta -> gamma e(+)e(-) decays and obtained upper limits of O(2 x 10(-6)) on U-gamma mixing at 90% C.L. for the mass range 30 < m(U) < 90 MeV/c(2). Combined with other experimental limits, the remaining region in the U-gamma mixing parameter space that can explain the (g - 2)(mu) deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29 < m(U) < 32 MeV/c(2) remaining.
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