This paper reports results for directed flow \(v_{1}\) and elliptic flow \(v_{2}\) of charged particles in Cu+Cu collisions at \(\sqrt{s_{NN}}=\) 22.4 GeV at the Relativistic Heavy Ion Collider. The ...measurements are for the 0-60% most central collisions, using charged particles observed in the STAR detector. Our measurements extend to 22.4 GeV Cu+Cu collisions the prior observation that \(v_1\) is independent of the system size at 62.4 and 200 GeV, and also extend the scaling of \(v_1\) with \(\eta/y_{\rm beam}\) to this system. The measured \(v_2(p_T)\) in Cu+Cu collisions is similar for \(\sqrt{s_{NN}} = 22.4-200\) GeV. We also report a comparison with results from transport model (UrQMD and AMPT) calculations. The model results do not agree quantitatively with the measured \(v_1(\eta), v_2(p_T)\) and \(v_2(\eta)\).
We present STAR measurements of azimuthal anisotropy by means of the two- and four-particle cumulants \(v_2\) (\(v_2\{2\}\) and \(v_2\{4\}\)) for Au+Au and Cu+Cu collisions at center of mass energies ...\(\sqrt{s_{_{\mathrm{NN}}} = 62.4\) and 200 GeV. The difference between \(v_2\{2\}^2\) and \(v_2\{4\}^2\) is related to \(v_{2}\) fluctuations (\(\sigma_{v_2}\)) and nonflow \((\delta_{2})\). We present an upper limit to \(\sigma_{v_2}/v_{2}\). Following the assumption that eccentricity fluctuations \(\sigma_{\epsilon}\) dominate \(v_2\) fluctuations \(\frac{\sigma_{v_2}}{v_2} \approx \frac{\sigma_{\epsilon}}{\epsilon}\) we deduce the nonflow implied for several models of eccentricity fluctuations that would be required for consistency with \(v_2\{2\}\) and \(v_2\{4\}\). We also present results on the ratio of \(v_2\) to eccentricity.
Phys.Rev.Lett.97:132301,2006 We report the measurements of $\Sigma (1385)$ and $\Lambda (1520)$ production
in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR
collaboration. ...The yields and the $p_{T}$ spectra are presented and discussed
in terms of chemical and thermal freeze-out conditions and compared to model
predictions. Thermal and microscopic models do not adequately describe the
yields of all the resonances produced in central $Au+Au$ collisions. Our
results indicate that there may be a time-span between chemical and thermal
freeze-out during which elastic hadronic interactions occur.
We report measurements of transverse momentum $p_t$ spectra for ten event multiplicity classes of p-p collisions at $\sqrt{s} = 200$ GeV. By analyzing the multiplicity dependence we find that the ...spectrum shape can be decomposed into a part with amplitude proportional to multiplicity and described by a Lévy distribution on transverse mass $m_t$, and a part with amplitude proportional to multiplicity squared and described by a gaussian distribution on transverse rapidity $y_t$. The functional forms of the two parts are nearly independent of event multiplicity. The two parts can be identified with the soft and hard components of a two-component model of p-p collisions. This analysis then provides the first isolation of the hard component of the $p_t$ spectrum as a distribution of simple form on $y_t$.
We present a systematic analysis of two-pion interferometry in Au+Au collisions at \(\sqrt{s_{\rm{NN}}}\) = 62.4 GeV and Cu+Cu collisions at \(\sqrt{s_{\rm{NN}}}\) = 62.4 and 200 GeV using the STAR ...detector at RHIC. The multiplicity and transverse momentum dependences of the extracted correlation lengths (radii) are studied. The scaling with charged particle multiplicity of the apparent system volume at final interaction is studied for the RHIC energy domain. The multiplicity scaling of the measured correlation radii is found to be independent of colliding system and collision energy.
We report the measurements of \(\Sigma (1385)\) and \(\Lambda (1520)\) production in \(p+p\) and \(Au+Au\) collisions at \(\sqrt{s_{NN}} = 200\) GeV from the STAR collaboration. The yields and the ...\(p_{T}\) spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central \(Au+Au\) collisions. Our results indicate that there may be a time-span between chemical and thermal freeze-out during which elastic hadronic interactions occur.
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