phi meson production in d plus Au collisions at root s(NN)=200 GeV

The PHENIX Collaboration has measured phi meson production in d + Au collisions at root s(NN) = 200 GeV using the dimuon and dielectron decay channels. The phi meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 \u3c y \u3c 2.2 (-2.2 \u3c y \u3c -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity vertical bar y vertical bar \u3c 0.35 in the p(T) range below 7 GeV/c. The phi meson invariant yields and nuclear-modification factors as a function of p(T), rapidity, and centrality are reported. An enhancement of phi meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p + p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects

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

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 \u3c p(T) \u3c 5.0 GeV/c and 3.0 \u3c vertical bar eta vertical bar \u3c 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 \u3c vertical bar x(F)vertical bar \u3c 0.7, as well as transverse momentum (p(T)) from 1.0 \u3c p(T) \u3c 4.5 GeV/c. The asymmetry averaged over positive x(F) is \u3c A(N)\u3e = 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

Measurements of directed, elliptic, and triangular flow in Cu plus Au collisions at root sNN=200 GeV

Measurements of anisotropic flow Fourier coefficients (upsilon(n)) for inclusive charged particles and identified hadrons pi(+/-), K-+/-, p, and (p) over bar produced at midrapidity in Cu + Au collisions at root s(NN) = 200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes psi(n), for n = 1, 2, and 3 are studied as a function of transverse momentum p(T) over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared with hydrodynamical and transport model calculations. We also compare these Cu + Au results with those in Cu + Cu and Au + Au collisions at the same root s(NN) and find that the upsilon(2) and upsilon(3), as a function of transverse momentum, follow a common scaling with 1/(epsilon N-n(part)1/3)

Low-mass vector-meson production at forward rapidity in p plus p collisions at root s=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, omega, rho, and phi, production through the dimuon decay channel at forward rapidity (1.2 \u3c vertical bar y vertical bar \u3c 2.2) in p + p collisions at root s = 200 GeV. The differential cross sections for these mesons are measured as a function of both p(T) and rapidity. We also report the integrated differential cross sections over 1 \u3c p(T) \u3c 7 GeV/c and 1.2 \u3c vertical bar y vertical bar \u3c 2.2: d sigma/dy(omega + rho rho -\u3e mu mu) = 80 +/- 6(stat) +/- 12(syst)nb and d sigma/dy(phi -\u3e mu mu) = 27 +/- 3(stat) +/- 4(syst)nb. These results are compared with midrapidity measurements and calculations

Centrality-Dependent Modification of Jet-Production Rates in Deuteron-Gold Collisions at root s(NN)=200 GeV

Jet production rates are measured in p + p and d + Au collisions at root s(NN) = 200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the R = 0.3 anti-k(t) algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multiwire proportional chambers, and the jet transverse momentum (p(T)) spectra are corrected for the detector response. Spectra are reported for jets with 12 \u3c p(T) \u3c 50 GeV/c, within a pseudorapidity acceptance of vertical bar eta vertical bar \u3c 0.3. The nuclear-modification factor (R-dAu) values for 0%-100% d + Au events are found to be consistent with unity, constraining the role of initial state effects on jet production. However, the centrality-selected RdAu values and central-to-peripheral ratios (R-CP) show large, p(T)-dependent deviations from unity, challenging the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei

Measurement of emission-angle anisotropy via long-range angular correlations with high-pT hadrons in d + Au and p + p collisions at √sNN = 200 GeV

We present measurements of two-particle angular correlations between high-transverse-momentum (2 \u3c pT \u3c 11 GeV/c) pi(0) observed at midrapidity (|eta| \u3c 0.35) and particles produced either at forward (3.1 \u3c eta \u3c 3.9) or backward (-3.7 \u3c eta \u3c -3.1) rapidity in d + Au and p + p collisions at root s(NN) = 200 GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a characteristic structure that persists up to pT approximate to 6 GeV/c and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A + A collisions. The structure is absent in the d-going direction as well as in p + p collisions, in the transverse-momentum range studied. The results indicate that the structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions

Dielectron production in Au plus Au collisions at root s(NN)=200 GeV

We present measurements of e(+)e-production at midrapidity in Au + Au collisions at root s(NN) = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (m(ee) \u3c 5 GeV/c(2)) and pair transverse momentum (p(T) \u3c 5 GeV/c) for minimum bias and for five centrality classes. The e(+)e(-) yield is compared to the expectations from known sources. In the low-mass region (m(ee) = 0.30-0.76 GeV/c(2)) there is an enhancement that increases with centrality and is distributed over the entire pair p(T) range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(model) or to 1.7 +/- 0.3(stat) +/- 0.3(syst) +/- 0.2(model) for minimum bias collisions when the open heavy-flavor contribution is calculated with PYTHIA or MC@NLO, respectively. The inclusive mass and p(T) distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the rho meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (m(ee) = 1.2-2.8 GeV/c(2)), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons

phi meson production in the forward/backward rapidity region in Cu plus Au collisions at root s(NN)=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured phi meson production and its nuclear modification in asymmetric Cu + Au heavy-ion collisions at root s(NN) = 200 GeV at both forward Cu-going direction (1.2 \u3c y \u3c 2.2) and backward Au-going direction (-2.2 \u3c y \u3c -1.2) rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0%-20% centrality, the phi meson yield integrated over 1 \u3c pT \u3c 5 GeV/c prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu + Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in d + Au collisions for these rapidities

Azimuthally anisotropic emission of low-momentum direct photons in Au plus Au collisions at root S-NN=200 GeV

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider has measured second- and third-order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in Au + Au collisions at root S-NN = 200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of 0.4 \u3c p(T) \u3c 4.0 GeV/c. At low p(T) the second-order coefficients, nu(2), are similar to the ones observed in hadrons. Third-order coefficients, nu(3), are nonzero and almost independent of centrality. These new results on nu(2) and nu(3), combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies

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

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) -\u3e pi(0)(-\u3e gamma gamma) pi(0)(-\u3e gamma gamma) and K*(0) -\u3e 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, show an 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) \u3e 5 GeV/c, production of all particles is similarly suppressed by a factor of approximate to 2