277 research outputs found

    Non-Gaussian Effects in Identical Pion Correlation Function at STAR

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    Preliminary femtoscopic results on identical pions from high statistics data set of Au+Au collisions at sqrt{s_NN}=200 GeV taken during the fourth RHIC run are presented. The measured three-dimensional correlation function is studied at low relative momenta using the Gaussian parametrization and the Levy stable parametrization. The latter is expected to better describe the data. As the results show, both parametrizations underestimate the peak of the measured correlation function equally.Comment: 6 pages, 3 figures; proceedings contribution to the Workshop on Particle Correlations and Femtoscopy, Kromeriz, Czech Republic, 15-17 Aug. 200

    A Fast Hadron Freeze-out Generator

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    We have developed a fast Monte Carlo procedure of hadron generation allowing one to study and analyze various observables for stable hadrons and hadron resonances produced in ultra-relativistic heavy ion collisions. Particle multiplicities are determined based on the concept of chemical freeze-out. Particles can be generated on the chemical or thermal freeze-out hypersurface represented by a parameterization or a numerical solution of relativistic hydrodynamics with given initial conditions and equation of state. Besides standard space-like sectors associated with the volume decay, the hypersurface may also include non-space-like sectors related to the emission from the surface of expanding system. For comparison with other models and experimental data we demonstrate the results based on the standard parameterizations of the hadron freeze-out hypersurface and flow velocity profile under the assumption of a common chemical and thermal freeze-out. The C++ generator code is written under the ROOT framework and is available for public use at http://uhkm.jinr.ru/.Comment: 28 pages,7 figure

    Spin alignment measurements of the K0(892)K^{*0}(892) and ϕ(1020)\phi(1020) vector mesons at RHIC

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    We present the first spin alignment measurements for the K0(892)K^{*0}(892) and ϕ(1020)\phi(1020) vector mesons produced at mid-rapidity with transverse momenta up to 5 GeV/c at sNN\sqrt{s_{NN}} = 200 GeV at RHIC. The diagonal spin density matrix elements with respect to the reaction plane in Au+Au collisions are ρ00\rho_{00} = 0.32 ±\pm 0.04 (stat) ±\pm 0.09 (syst) for the K0K^{*0} (0.8<pT<5.00.8<p_T<5.0 GeV/c) and ρ00\rho_{00} = 0.34 ±\pm 0.02 (stat) ±\pm 0.03 (syst) for the ϕ\phi (0.4<pT<5.00.4<p_T<5.0 GeV/c), and are constant with transverse momentum and collision centrality. The data are consistent with the unpolarized expectation of 1/3 and thus no evidence is found for the transfer of the orbital angular momentum of the colliding system to the vector meson spins. Spin alignments for K0K^{*0} and ϕ\phi in Au+Au collisions were also measured with respect to the particle's production plane. The ϕ\phi result, ρ00\rho_{00} = 0.41 ±\pm 0.02 (stat) ±\pm 0.04 (syst), is consistent with that in p+p collisions, ρ00\rho_{00} = 0.39 ±\pm 0.03 (stat) ±\pm 0.06 (syst), also measured in this work. The measurements thus constrain the possible size of polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo corrected, published in PRC.77.06190

    System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider

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    We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)

    Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV

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    We report a new STAR measurement of the longitudinal double-spin asymmetry A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit of polarized deep-inelastic scattering measurements.Comment: 7 pages, 4 figures + 1 tabl

    Measurements of ϕ\phi meson production in relativistic heavy-ion collisions at RHIC

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    We present results for the measurement of ϕ\phi meson production via its charged kaon decay channel ϕK+K\phi \to K^+K^- in Au+Au collisions at sNN=62.4\sqrt{s_{_{NN}}}=62.4, 130, and 200 GeV, and in p+pp+p and dd+Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV from the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC). The midrapidity (y<0.5|y|<0.5) ϕ\phi meson transverse momentum (pTp_{T}) spectra in central Au+Au collisions are found to be well described by a single exponential distribution. On the other hand, the pTp_{T} spectra from p+pp+p, dd+Au and peripheral Au+Au collisions show power-law tails at intermediate and high pTp_{T} and are described better by Levy distributions. The constant ϕ/K\phi/K^- yield ratio vs beam species, collision centrality and colliding energy is in contradiction with expectations from models having kaon coalescence as the dominant mechanism for ϕ\phi production at RHIC. The Ω/ϕ\Omega/\phi yield ratio as a function of pTp_{T} is consistent with a model based on the recombination of thermal ss quarks up to pT4p_{T}\sim 4 GeV/cc, but disagrees at higher transverse momenta. The measured nuclear modification factor, RdAuR_{dAu}, for the ϕ\phi meson increases above unity at intermediate pTp_{T}, similar to that for pions and protons, while RAAR_{AA} is suppressed due to the energy loss effect in central Au+Au collisions. Number of constituent quark scaling of both RcpR_{cp} and v2v_{2} for the ϕ\phi meson with respect to other hadrons in Au+Au collisions at sNN\sqrt{s_{_{NN}}}=200 GeV at intermediate pTp_{T} is observed. These observations support quark coalescence as being the dominant mechanism of hadronization in the intermediate pTp_{T} region at RHIC.Comment: 22 pages, 21 figures, 4 table

    Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV

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    We report on the observed differences in production rates of strange and multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp interactions at the same energy. The strange baryon yields in Au+Au collisions, then scaled down by the number of participating nucleons, are enhanced relative to those measured in pp reactions. The enhancement observed increases with the strangeness content of the baryon, and increases for all strange baryons with collision centrality. The enhancement is qualitatively similar to that observed at lower collision energy sqrts =17.3 GeV. The previous observations are for the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR

    Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at sNN\sqrt{s_{NN}} = 200 GeV

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    Forward-backward multiplicity correlation strengths have been measured with the STAR detector for Au+Au and p+p\textit{p+p} collisions at sNN\sqrt{s_{NN}} = 200 GeV. Strong short and long range correlations (LRC) are seen in central Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in peripheral Au+Au collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate (CGC) predict the existence of the long range correlations. In the DPM the fluctuation in the number of elementary (parton) inelastic collisions produces the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is in qualitative agreement with the predictions from the DPM and indicates the presence of multiple parton interactions.Comment: 6 pages, 3 figures The abstract has been slightly modifie

    Hadronic resonance production in dd+Au collisions at sNN\sqrt{s_{_{NN}}} = 200 GeV at RHIC

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    We present the first measurements of the ρ(770)0\rho(770)^0, KK^*(892), Δ\Delta(1232)++^{++}, Σ\Sigma(1385), and Λ\Lambda(1520) resonances in dd+Au collisions at sNN\sqrt{s_{_{NN}}} = 200 GeV, reconstructed via their hadronic decay channels using the STAR detector at RHIC. The masses and widths of these resonances are studied as a function of transverse momentum (pTp_T). We observe that the resonance spectra follow a generalized scaling law with the transverse mass (mTm_T). The ofresonancesinminimumbiascollisionsiscomparedtothe of resonances in minimum bias collisions is compared to the of π\pi, KK, and pˉ\bar{p}. The ρ0/π\rho^0/\pi^-, K/KK^*/K^-, Δ++/p\Delta^{++}/p, Σ(1385)/Λ\Sigma(1385)/\Lambda, and Λ(1520)/Λ\Lambda(1520)/\Lambda ratios in dd+Au collisions are compared to the measurements in minimum bias p+pp+p interactions, where we observe that both measurements are comparable. The nuclear modification factors (RdAuR_{dAu}) of the ρ0\rho^0, KK^*, and Σ\Sigma^* scale with the number of binary collisions (NbinN_{bin}) for pT>p_T > 1.2 GeV/cc.Comment: STAR Collaboration. Submitted to PR

    Correlations in STAR: interferometry and event structure

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    STAR observes a complex picture of RHIC collisions where correlation effects of different origins -- initial state geometry, semi-hard scattering, hadronization, as well as final state interactions such as quantum intensity interference -- coexist. Presenting the measurements of flow, mini-jet deformation, modified hadronization, and the Hanbury Brown and Twiss effect, we trace the history of the system from the initial to the final state. The resulting picture is discussed in the context of identifying the relevant degrees of freedom and the likely equilibration mechanism.Comment: 8 pages, 6 figures, plenary talk at the 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, to appear in Journal of Physics G (http://www.iop.org
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