Here, elliptic flow measurements from two-, four- and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at $\sqrt{s_{NN}}$ = 193 GeV, Cu+Au at $\sqrt{s_{NN}}$ = ...200 GeV and Au+Au spanning the range $\sqrt{s_{NN}}$ = 11.5 - 200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and Glauber model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.
According to first principle Lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region µB ≤ Tc. As a result, higher-order cumulants and ...their ratios are predicted to be negative, C6/C2 < 0, for example. In this paper, we report the first measurement of the midrapidity net-proton C6/C2 from 27, 54.4 and 200 GeV Au+Au collisions at RHIC. The dependence on collision centrality and kinematic acceptance in (pT, y) are analyzed. While for 27 and 54.4 GeV collisions the C6/C2 values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the C6/C2 ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict values around zero. These observations seem to favor a smooth crossover in the high energy nuclear collisions at RHIC.
According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region μB≤Tc. In this range the ratio, C6/C2, of ...net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton C6/C2 from 27, 54.4, and 200 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in (pT, y) are analyzed. While for 27 and 54.4 GeV collisions the C6/C2 values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the C6/C2 ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.
Global polarization of Ξ and Ω hyperons has been measured for the first time in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. The measurements of the $Ξ^{-}$ and $\overline{Ξ}^{+}$ hyperon ...polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay Ξ→Λ+π, as well as by measuring the polarization of the daughter Λ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $Ξ^{-}$ and $\overline{Ξ}^{+}$, is measured to be $\langle{P_{Ξ}}\rangle$=0.47±0.10(stat)±0.23(syst)% for the collision centrality 20%-80%. The $\langle{P_{Ξ}}\rangle$ is found to be slightly larger than the inclusive Λ polarization and in reasonable agreement with a multiphase transport model. The $\langle{P_{Ξ}}\rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. Finally, the global polarization of Ω, $\langle{P_{Ω}}\rangle$=1.11±0.87(stat)±1.97(syst)% was obtained by measuring the polarization of daughter Λ in the decay Ω→Λ+K, assuming the polarization transfer factor $C_{ΩΛ}=1$.
We report on new measurements of inclusive J/ψ polarization at mid-rapidity in p+p collisions at √s = 200 GeV by the STAR experiment at RHIC. The polarization parameters, λθ, λφ, and λθφ, are ...measured as a function of transverse momentum (pT) in both the Helicity and CollinsSoper (CS) reference frames within pT < 10 GeV/c. Except for λθ in the CS frame at the highest measured pT, all three polarization parameters are consistent with 0 in both reference frames without any strong pT dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with non-relativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
We report on new measurements of inclusive J/ψ polarization at mid-rapidity in p+p collisions at $\sqrt{s}$ = 200 GeV by the STAR experiment at RHIC. The polarization parameters, λθ, λφ, and λθφ, are ...measured as a function of transverse momentum (pT) in both the Helicity and CollinsSoper (CS) reference frames within pT < 10 GeV/c. Except for λθ in the CS frame at the highest measured pT, all three polarization parameters are consistent with 0 in both reference frames without any strong pT dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with non-relativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum ...chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in Au+Au collisions at a nucleon-nucleon center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen in midcentral (intermediate impact parameter) collisions. Significant residual background effects may, however, still be present.
According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region μ_{B}≤T_{c}. In this range the ratio, C_{6}/C_{2}, ...of net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton C_{6}/C_{2} from 27, 54.4, and 200 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in (p_{T}, y) are analyzed. While for 27 and 54.4 GeV collisions the C_{6}/C_{2} values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the C_{6}/C_{2} ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.
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