Suppression of the J/ψ nuclear-modification factor has been seen as a trademark signature of final-state effects in large collision systems for decades. In small systems, the nuclear modification was ...attributed to cold-nuclear-matter effects until the observation of strong differential suppression of the ψ(2S) state in p+A and d+A collisions suggested the presence of final-state effects. Results of J/ψ and ψ(2S) measurements in the dimuon decay channel are presented here for p+p, p+Al, and p+Au collision systems at sNN=200GeV. The results are predominantly shown in the form of the nuclear-modification factor, RpA, the ratio of the ψ(2S) invariant yield per nucleon-nucleon collision in collisions of proton on target nucleus to that in p+p collisions. Measurements of the J/ψ and ψ(2S) nuclear-modification factor are compared with shadowing and transport-model predictions, as well as to complementary measurements at Large Hadron Collider energies.
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.
We present a measurement of the transverse single-spin asymmetry for π0 and η mesons in p↑+ p collisions in the pseudorapidity range |η| < 0.35 and at a center-of-mass energy of 200 GeV with the ...PHENIX detector at the Relativistic Heavy Ion Collider. In comparison with previous measurements in this kinematic region, these results have factor-of-3-smaller uncertainties. As hadrons, π0 and η mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Comparisons of the differences in their transverse single-spin asymmetries have the potential to disentangle the possible effects of strangeness, isospin, or mass. These results can constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function.
We report the transverse single-spin asymmetries of J/ψ production at forward and backward rapidity, 1.2<|y|<2.2, as a function of J/ψ transverse momentum (pT) and Feynman-x (xF). The data analyzed ...were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from p+p, p+Al, and p+Au collisions with transversely polarized proton beams at sNN=200 GeV. At this collision energy, single-spin asymmetries for heavy-flavor particle production of p+p collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. Proton+nucleus collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate a positive asymmetry at the two-standard-deviation level in the p+p data for 2 GeV/c<pT<10 GeV/c at backward rapidity and negative asymmetries at the two-standard-deviation level in the p+Au data for pT<2 GeV/c at both forward and backward rapidity, while in p+Al collisions the asymmetries are consistent with zero within the range of experimental uncertainties.
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.
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|
We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively charged hadrons in polarized p↑+p, p↑+Al, and p↑+Au collisions at sNN=200 GeV. The ...measurements have been performed at forward rapidity (1.4<η<2.4) over the range of transverse momentum (1.8<pT<7.0 GeV/c) and Feynman x (0.1<xF<0.2). We observed positive asymmetries for positively charged hadrons in p↑+p collisions, and significantly reduced asymmetries in p↑+A collisions. These results reveal a nuclear dependence of TSSAs for charged-hadron production in a regime where perturbative techniques are applicable. These results provide new opportunities to use p↑+A collisions as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions and to use TSSAs as a new handle in studying small-system collisions.
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