Measurements of azimuthal anisotropy and charged-particle multiplicity in dd++Au collisions at sNN=\sqrt{s_{_{NN}}}=200, 62.4, 39, and 19.6 GeV

International audienceWe present measurements of the elliptic flow (v2) as a function of transverse momentum (pT), pseudorapidity (η), and centrality in d+Au collisions at sNN=200, 62.4, 39, and 19.6 GeV. The beam-energy scan of d+Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero v2 signal at all four collision energies, which, at midrapidity and low pT, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the ampt Monte Carlo generator) show good agreement with the data at midrapidity to forward (d-going) rapidities and low pT. At backward (Au-going) rapidities and pT>1.5GeV/c, the data diverges from ampt calculations of v2 relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity (dNch/dη) as a function of η in central d+Au collisions at the same energies. We find that in d+Au collisions at sNN=200 GeV the v2 scales with dNch/dη over all η in the PHENIX acceptance. At sNN=62.4, and 39 GeV, v2 scales with dNch/dη at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the dNch/dη scaling may be a further indication of nonflow effects dominating at backward rapidity

Measurements of mass-dependent azimuthal anisotropy in central pp++Au, dd++Au, and 3^3He++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

International audienceWe present measurements of the transverse-momentum dependence of elliptic flow v2 for identified pions and (anti)protons at midrapidity (|η|<0.35), in 0%–5% central p+Au and He3+Au collisions at sNN=200 GeV. When taken together with previously published measurements in d+Au collisions at sNN=200 GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries. We observe a clear mass-dependent splitting of v2(pT) in d+Au and He3+Au collisions, just as in large nucleus-nucleus (A+A) collisions, and a smaller splitting in p+Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low pT (<1.5GeV/c), but fail to describe various features at higher pT. In all systems, the v2 values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark (KET/nq), which was also seen previously in A+A collisions

Measurement of ϕ\phi-meson production at forward rapidity in p+pp+p collisions at s=510 GeV\sqrt{s}=510\text{ }\text{ }\mathrm{GeV} and its energy dependence from s=200 GeV\sqrt{s}=200\text{ }\text{ }\mathrm{GeV} to 7 TeV

International audienceThe PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of ϕ(1020)-meson production at forward rapidity in p+p collisions at s=510  GeV via the dimuon decay channel. The partial cross section in the rapidity and pT ranges 1.2<|y|<2.2 and 2<pT<7  GeV/c is σϕ=[2.28±0.09(stat)±0.14(syst)±0.27(norm)]×10-2  mb. The energy dependence of σϕ (1.2<|y|<2.2,2<pT<5  GeV/c) is studied using the PHENIX measurements at s=200 and 510 GeV and the Large Hadron Collider measurements at s=2.76 and 7 TeV. The experimental results are compared to various event generator predictions (pythia6, pythia8, phojet, ampt, epos3, and epos-lhc)

Lévy-stable two-pion Bose-Einstein correlations in sNN=200\sqrt{s_{NN}}=200 GeV Au++Au collisions

International audienceWe present a detailed measurement of charged two-pion correlation functions in 0–30% centrality sNN=200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair mT. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(mT) measurements indicate a decrease of the strength of the correlations at low mT. The Lévy length scale parameter R(mT) decreases with increasing mT, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α=2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition

Measurement of two-particle correlations with respect to second- and third-order event planes in Au++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

International audienceWe present measurements of azimuthal correlations of charged hadron pairs in sNN=200 GeV Au+Au collisions for the trigger and associated particle transverse-momentum ranges of 14GeV/c) correlations is suppressed compared with that of correlations measured in p+p collisions. At the lowest associated particle pT(0.5<pTa<1GeV/c), the away-side shape and yield are modified relative to those in p+p collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-pT trigger correlations (2<pTt<4GeV/c), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle Ψ2 and Ψ3. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the Ψ2 event plane. This asymmetry and the measured suppression of the pair yield out-of-plane is consistent with a path-length-dependent energy loss. No Ψ3 dependence can be resolved within experimental uncertainties

BB-meson production at forward and backward rapidity in p+pp+p and Cu + Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

International audienceThe fraction of J/ψ mesons which come from B-meson decay, FB→J/ψ, is measured for J/ψ rapidity 1.20 in p+p and Cu+Au collisions at sNN = 200 GeV with the PHENIX detector. The extracted fraction is FB→J/ψ=0.025±0.006 (stat) ± 0.010(syst) for p+p collisions. For Cu+Au collisions, FB→J/ψ is 0.094 ± 0.028(stat) ± 0.037(syst) in the Au-going direction (−2.2<y<−1.2) and 0.089 ± 0.026(stat) ± 0.040(syst) in the Cu-going direction (1.2<y<2.2). The nuclear modification factor, RCuAu, of B mesons in Cu+Au collisions is consistent with binary scaling of measured yields in p+p at both forward and backward rapidity

Measurements of e+e−e^+e^- pairs from open heavy flavor in pp+pp and dd+AA collisions at sNN=200\sqrt{s_{NN}}=200 GeV

International audienceWe report a measurement of e+e− pairs from semileptonic heavy-flavor decays in p+p collisions at sNN=200 GeV. The e+e− pair yield from bb¯ and cc¯ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e− spectra from cc¯ and bb¯ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for bb¯ than for cc¯. The same model dependence was observed in already published d+A data. The p+p data are also directly compared with d+A data in mass and pT, and within the statistical accuracy no nuclear modification is seen