We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and minimum bias p+p collisions at sNN=200 GeV. The charged hadron is ...measured at midrapidity |eta|<0.35, and the energy is measured at large rapidity (-3.7<eta< -3.1, Au-going direction). An enhanced near-side angular correlation across | Delta eta|>2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v2 for inclusive charged hadrons at midrapidity up to pT=4.5 GeV/c. We also present the measurement of v2 for identified pi+ or - and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy-ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from p+Pb at sNN=5.02 TeV. The magnitude of the mass ordering in d+Au is found to be smaller than that in p+Pb collisions, which may indicate smaller radial flow in lower energy d+Au collisions.
The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au + Au collisions at root s(NN) = 200 GeV down to pT = 0.4 GeV/c. Photons are detected via photon ...conversions to e(+)e(-) pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the N-coll-scaled yield measured in p + p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/c in the pT range 0.6-2.0 GeV/c. While the shape of the pT distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with N-part(alpha), where alpha = 1.38 +/- 0.03(stat) +/- 0.07(syst).
We present results for three charmonia states (ψ′, χc, and J/ψ) in d+Au collisions at |y|<0.35 and sNN−−−√=200 GeV. We find that the modification of the ψ′ yield relative to that of the J/ψ scales ...approximately with charged particle multiplicity at midrapidity across p+A, d+Au, and A+A results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the ψ′ and J/ψ, while in small-impact-parameter collisions the more weakly bound ψ′ is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger ψ′ suppression in central events is not explained by an increase of the nuclear absorption owing to meson formation time effects.
In this paper, measurements of the anisotropic flow coefficients v2{Ψ2}, v3{Ψ3}, v4{Ψ4}, and v4{Ψ2} for identified particles (π±, K±, and p + ¯p) at midrapidity, obtained relative to the event planes ...Ψm at forward rapidities in Au + Au collisions at sNN=200 GeV , are presented as a function of collision centrality and particle transverse momenta pT. The vn coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic n, a modified valence quark-number Nq scaling plotting vn{Ψm}/(Nq)n/2 versus transverse kinetic energies (KET)/Nq is observed to yield a single curve for all the measured particle species for a broad range of KET . A simultaneous blast-wave model fit to the observed vn{Ψm}(pT) coefficients and published particle spectra identifies radial flow anisotropies ρn{Ψm} and spatial eccentricities sn{Ψm} at freeze-out. Finally, these are generally smaller than the initial-state participant-plane geometric eccentricities εn {ΨPPm} as also observed in the final eccentricity from quantum interferometry measurements with respect to the event plane.
We present results for three charmonia states (psi' chi(c), and J/ psi) in d + Au collisions at vertical bar y vertical bar < 0.35 and root s(NN) = 200 GeV. We find that the modification of the psi' ...yield relative to that of the J/ psi scales approximately with charged particle multiplicity at midrapidity across p + A, d + Au, and A + A results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the psi' and J/ psi, while in small-impact-parameter collisions the more weakly bound psi' is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger psi' suppression in central events is not explained by an increase of the nuclear absorption owing to meson formation time effects.
The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at sNN=200 GeV in the ...transverse-momentum range 0.85≤peT≤8.5 GeV/c. In central d+Au collisions, the nuclear modification factor RdA at 1.5<pT<5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p+p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the π0 and heavy-flavor-electron nuclear modification factors RAA.
Direct photons have been measured in √sNN=200 GeV d+Au collisions at midrapidity. A wide pT range is covered by measurements of nearly real virtual photons (1<pT<6 GeV/c) and real photons (5<pT<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 pT range. This indicates that the large enhancement of direct photons observed in Au+Au collisions for 1.0<pT<2.5 GeV/c is attributable to a source other than the initial-state nuclear effects.
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.
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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