System size, energy and pseudorapidity dependence of directed and elliptic flow at RHIC

Elliptic flow measurements from two-, four- and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at $\sqrt{s_{\rm NN}}$= 193 GeV, Cu+Au at $\sqrt{s_{\rm NN}}$= 200 GeV and Au+Au spanning the range $\sqrt{s_{\rm NN}}$= 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 re...

We show that the centrality and system-size dependence of elliptic flow measured at RHIC are fully described by a simple model based on eccentricity scaling and incomplete thermalization. We argue that the elliptic flow is at least 25% below the (ideal) ``hydrodynamic limit'', even for the most central Au-Au collisions. This lack of perfect equilibration allows for estimates of the effective parton cross section in the Quark-Gluon Plasma and of its viscosity to entropy densit...

Directed flow, v1, of charged hardons has been measured in Au-Au collisions at RHIC for center-of-mass energies sqrt(sNN) = 19.6, 130, 62.4, and 200 GeV using the PHOBOS detector. The large acceptance of PHOBOS for charged particles allows measurements over the full range of pseudorapidity |eta| <5.4. The results for a symmetric subevent method are shown at all four energies. Comparison is made to a mixed harmonic method for the highest energy, and compared to similar results...

Detailed differential measurements of the elliptic flow for particles produced in Au+Au and Cu+Cu collisions at sqrt(s_NN) = 200 GeV are presented. Predictions from perfect fluid hydrodynamics for the scaling of the elliptic flow coefficient v_2 with eccentricity, system size and transverse energy are tested and validated. For transverse kinetic energies KE_T ~ m_T-m up to ~1 GeV, scaling compatible with the hydrodynamic expansion of a thermalized fluid is observed for all pr...

We report first results on elliptic flow of identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow. The fit to the data with a simple...

We employed the new issue of a parton and hadron cascade model PACIAE 2.1 to systematically investigate the charged particle elliptic flow parameter $v_2$ in the relativistic nuclear collisions at RHIC and LHC energies. With randomly sampling the transverse momentum $x$ and $y$ components of the particles generated in string fragmentation on the circumference of an ellipse instead of circle originally, the calculated charged particle $v_2(\eta)$ and $v_2(p_T)$ fairly reproduc...

The elliptic flow measured at RHIC has been interpreted as a signature for strong partonic interactions early in the collision and as an indication of a well developed quark-gluon plasma phase. The measured values of elliptic flow, using methods based on multi-particle correlations, are affected by fluctuations in the magnitude of the elliptic flow. In this Letter, using a Monte Carlo Glauber calculation, we estimate what the possible effect of spatial eccentricity fluctuatio...

Elliptic flow is a hallmark of collectivity in hadronic collisions. Its measurement relies on analysis techniques which require high event multiplicity and could be applied so far to heavy ion collisions only. Here, we delineate the conditions under which elliptic flow becomes measurable in the samples of high-multiplicity ($dN_{\rm ch}/dy \geq 50$) p-p collisions, which will soon be collected at the LHC. We observe that fluctuations in the p-p interaction region can result i...

We report the elliptic flow of charged and identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The integrated elliptic flow signal, $v_2$, for charged particles reaches values of about 0.06, indicating a higher degree of thermalization than at lower energies. The differential elliptic flow signal, $v_2$($p_t$) up to 1.5 GeV/$c$, shows a behavior expected from hydrodynamic model calculations. Above 1.5 GeV/$c$, the...

Elliptic flow has been measured by the BRAHMS experiment as a function of transverse momentum and pseudorapidity for the Au+Au reaction at sqrt[s_{NN}] = 200 GeV. Identified-particle v2 (eta, pt) values were obtained with the two BRAHMS spectrometers at pseudorapidities eta approximately equal to 0, 1, and 3.4. The results show that the differential v2(eta, pt) values for a given particle type are essentially constant over the covered pseudorapidity range. It is suggested tha...