Angular distributions of charged particles relative to jet axes are studied in $\sqrt{^SNN}$ = 200 GeV Au+Au collisions as a function of the jet orientation with respect to the event plane. This ...differential study tests the expected path-length dependence of energy loss experienced by a hard-scattered parton as it traverses the hot and dense medium formed in heavy-ion collisions. A second-order event plane is used in the analysis as an experimental estimate of the reaction plane formed by the collision impact parameter and the beam direction. Charged-particle jets with 15 < $p_{\text {T,jet}}$ < 20 and 20 < $p_{\text {T,jet}}$ < 40 GeV / $c$ were reconstructed with the anti-$k_{\text {T}}$ algorithm with radius parameter setting of R = 0.4 in the 20-50% centrality bin to maximize the initial-state eccentricity of the interaction region. The reaction plane fit method is implemented to remove the flow-modulated background with better precision than prior methods. Yields and widths of jet-associated charged-hadron distributions are extracted in three angular bins between the jet axis and the event plane. The event-plane (EP) dependence is further quantified by ratios of the associated yields in different EP bins. No dependence on orientation of the jet axis with respect to the event plane is seen within the uncertainties in the kinematic regime studied. Finally, this finding is consistent with a similar experimental observation by ALICE in $\sqrt{^SNN}$ = 2.76 TeV Pb-Pb collision data.
The PHENIX experiment has studied nuclear effects in p+Al and p+Au collisions at sNN=200GeV on charged hadron production at forward rapidity (1.4<η<2.4, p-going direction) and backward rapidity ...(-2.2<η<-1.2, A-going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central p+Al and p+Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in p+p collisions. The magnitude of enhancement at backward rapidity is larger in p+Au collisions than in p+Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.
We 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.
Presented are the first measurements of the transverse single-spin asymmetries (AN) for neutral pions and eta mesons in p+Au and p+Al collisions at sNN=200 GeV in the pseudorapidity range |η|
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