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Register a new userEnergy and System-Size Dependence of Long-Range Multiplicity Correlations from the STAR Experiment
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Terence J. Tarnowsky
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A discussion of results for short and long-range multiplicity correlations (forward-backward) are presented for several systems (Au+Au, Cu+Cu, and pp) and energies (e.g. $sqrt{s_{NN}}$ = 200, 62.4, and $approx$ 20 GeV). These correlations are measured with increasing values of a gap in pseudorapidity, from no gap at midrapidity to a separation of 1.6 units ($|eta|$ = 0.8). For the highest energy, central A+A collisions, the forward-backward correlation strength maintains a constant value across the measurement region. In peripheral collisions, at lower energies, and in pp data, the maximum appears at midrapidity. This result may indicate the possible formation of high density matter for central A+A collisions at $sqrt{s_{NN}}$ = 200 GeV.
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Two-particle azimuthal ($Deltaphi$) and pseudorapidity ($Deltaeta$) correlations using a trigger particle with large transverse momentum ($p_T$) in $d$+Au, Cu+Cu and Au+Au collisions at $sqrt{s_{{NN}}}$ =xspace 62.4 GeV and 200~GeV from the STAR experiment at RHIC are presented. The s correlation is separated into a jet-like component, narrow in both $Deltaphi$ and $Deltaeta$, and the ridge, narrow in $Deltaphi$ but broad in $Deltaeta$. Both components are studied as a function of collision centrality, and the jet-like correlation is studied as a function of the trigger and associated $p_T$. The behavior of the jet-like component is remarkably consistent for different collision systems, suggesting it is produced by fragmentation. The width of the jet-like correlation is found to increase with the system size. The ridge, previously observed in Au+Au collisions at $sqrt{s_{{NN}}}$ = 200 GeV, is also found in Cu+Cu collisions and in collisions at $sqrt{s_{{NN}}}$ =xspace 62.4 GeV, but is found to be substantially smaller at $sqrt{s_{{NN}}}$ =xspace 62.4 GeV than at $sqrt{s_{{NN}}}$ = 200 GeV for the same average number of participants ($ langle N_{mathrm{part}}rangle$). Measurements of the ridge are compared to models.
This paper presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.
We present data on long-range multiplicity correlations in ultra-relativistic heavy ion collisions at the top RHIC energy ($sqrt{s_{NN}}$ = 200 GeV) from the STAR experiment. The data shows a long-range multiplicity correlation extending across a gap of 1.6 units in pseudorapidity. The data is over predicted by a multiparticle production model with hadronization of independent strings, or fusion of two color strings. This can be interpreted in terms of additional dynamical reduction in the number of particle sources.
We present a system size and energy dependence of $phi$ meson production in Cu+Cu and Au+Au collisions at $sqrt{s_{NN}}$=62.4 GeV and 200 GeV measured by the STAR experiment at RHIC. We find that the number of participant scaled $phi$ meson yields in heavy ion collisions over that of p+p collisions are larger than 1 and increase with collision energy. We compare the results with those of open-strange particles and discuss the physics implication.
We present measurements of net charge fluctuations in $Au + Au$ collisions at $sqrt{s_{NN}} = $ 19.6, 62.4, 130, and 200 GeV, $Cu + Cu$ collisions at $sqrt{s_{NN}} = $ 62.4, 200 GeV, and $p + p$ collisions at $sqrt{s} = $ 200 GeV using the dynamical net charge fluctuations measure $ u_{+-{rm,dyn}}$. We observe that the dynamical fluctuations are non-zero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate $1/N_{ch}$ scaling, but display approximate $1/N_{part}$ scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.
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