We 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 ow 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 > 1:5 GeV/c, the data diverges from ampt calculations of v2 relative to the initial geometry, indicating the possible dominance of nongeometry related corre- lations, referred to as nonflow. We also present measurements of the charged-particle multiplicity (dNch/d ) 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/d over all in the PHENIX acceptance. At √sNN = 62:4, and 39 GeV, v2 scales with dNch/d at midrapidity and forward rapidity, but falls o at backward rapidity. Furthermore, this departure from the dNch/dη scaling may be a further indication of non ow effects dominating at backward rapidity.
Small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The ...identified-particle spectra, especially the ϕ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured ϕ mesons in a specific set of small collision systems p+Al, p+Au, and 3He+Au, as well as d+Au Adare et al., Phys. Rev. C 83, 024909 (2011), at √sNN=200 GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model predictions. The comparisons with different calculations suggest that quark-gluon plasma may be formed in these small collision systems at √sNN=200 GeV. However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. The comparison with calculations suggests that the main production mechanisms of ϕ mesons at midrapidity may be different in p+Al versus p/d/3He+Au collisions at √sNN=200 GeV. While thermal quark recombination seems to dominate in p/d/3He+Au collisions, fragmentation seems to be the main production mechanism in p+Al collisions.
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.
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