A Non-Zero Hadronic Elliptic Flow with a Vanished Partonic Elliptic Flow in a Coalescence Scenario

The elliptic flow of a hadron is calculated using a quark coalescence model based on the quark phase space distribution produced by a free streaming locally thermalized quark in a two-dimensional transverse plane at initial time. Without assuming the quark＇s elliptic flow, it is shown that the hadron obtains a non-zero elliptic flow in this model. The elliptic flow of the hadron is shown to be sensitive to both space momentum correlation and the hadron＇s internal structure. Quark number scaling is obtained only for some special cases.     

Eccentricity Scaling of Elliptic Flow in Relativistic Au+Au Collisions

Elliptic flow for Au＋Au non-central collisions at √SNN = 200 GeV is investigated within a （2＋ 1）-dimensiona＇l hydrodynamic model. The results show that the eccentricity scaling for the collisions is almost perfect. The evolution including the phase transition conforms to the demand of scaling invariance of hydrodynamics of the collision system.     

Effects of Surface Emitting and Cumulative Collisions on Elliptic Flow

The integral and differential elliptic flow of partons is calculated using the multiphase transport model for Au＋Au collisions at centre-of-mass energy √SNN=200 GeV. It is shown that elliptic flow of partons freezing out at early time, which is affected mainly by surface emittance, decreases with time and elliptic flow of partons freezing out at late time, which is dominated by cumulative collisions, increases with time. The elliptic flow of partons freezing out early has a large contribution to the flatting of curve of final differential elliptic flow at large transverse momentum. It is argued that the effect of surface emittance is not neglectable.     

NeXSPheRIO results on elliptic flow at RHIC and connection with thermalization

Elliptic flow at RHIC is computed event by event with NeXSPheRIO. Reasonable agreement with experimental results on v ₂(η) is obtained. Various effects are studied as well: reconstruction of impact parameter direction, freeze-out temperature, equation of state (with or without crossover), emission mechanism.     

Suppression of elliptic flow in a minimally viscous quark–gluon plasma

We compute the time evolution of elliptic flow in non-central relativistic heavy-ion collisions, using a (2+1$2+1$)-dimensional code with longitudinal boost-invariance to simulate viscous fluid dynamics in the causal Israel–Stewart formulation. We show that even “minimal” shear viscosity η/s=?/(4π)$\eta /s=?/(4\pi )$ leads to a large reduction of elliptic flow compared to ideal fluid dynamics, raising questions about the interpretation of recent experimental data from the Relativistic Heavy Ion Collider.     

Transverse radial expansion in nuclear collisions and two particle correlations

At the very first stage of an ultra-relativistic nucleus–nucleus collision new particles are produced in individual nucleon–nucleon collisions. In the transverse plane, all particles from a single NN collision are initially located at the same position. The subsequent thermalization and transverse radial expansion of the system create strong position-momentum correlations and lead to characteristic rapidity, transverse momentum, and azimuthal correlations among the produced particles.     

Momentum spectra,anisotropic flow,and ideal fluids

If the matter produced in ultrarelativistic heavy-ion collisions reaches thermal equilibrium, its subsequent evolution follows the laws of ideal fluid dynamics. We show that general predictions can be made on this basis alone, irrespective of the details of the hydrodynamical model. We derive several scaling rules for momentum spectra and anisotropic flow (in particular the elliptic flow, v₂$v_2$, and the hexadecupole flow, v₄$v_4$) of identified particles. Comparison with existing data is briefly discussed, and qualitative predictions are made for LHC.     

The directed flow maximum near cs = 0

We investigate the excitation function of quark-gluon plasma formation and of directed in-plane flow of nucleons in the energy range of the BNL-AGS and for the E ^kin _Lab = 40A GeV Pb + Pb collisions performed recently at the CERN-SPS. We employ the three-fluid model with dynamical unification of kinetically equilibrated fluid elements. Within our model with first-order phase transition at high density, droplets of QGP coexisting with hadronic matter are produced already at BNL-AGS energies, E ^kin _Lab≃ 10A GeV. A substantial decrease of the isentropic velocity of sound, however, requires higher energies, E ^kin _Lab≃ 40A GeV. We show the effect on the flow of nucleons in the reaction plane. According to our model calculations, kinematic requirements and EoS effects work hand-in-hand at E ^kin _Lab = 40A GeV to allow the observation of the dropping velocity of sound via an increase of the directed flow around midrapidity as compared to top BNL-AGS energy. Received: 7 May 2000 / Accepted: 2 August 2000     

Universal scaling of the elliptic flow data at RHIC

Recent PHOBOS measurements of the excitation function for the pseudo-rapidity dependence of the elliptic flow in Au + Au collisions at RHIC have posed a significant theoretical challenge. Here we show that these differential measurements, as well as the RHIC measurements on transverse momentum satisfy a universal scaling relation predicted by the Buda-Lund model, based on exact solutions of perfect fluid hydrodynamics. We also show that the recently found transverse kinetic energy scaling of the elliptic flow is a special case of this universal scaling.     

Jet quenching and elliptic flow

In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pT$p_T$ hadrons. Assuming that the deposited energy quickly thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP fluid. Explicit simulation of Au + Au collision with and without a quenching jet indicate that elliptic flow is greatly reduced in a jet event. The result can be used to identify the jet events in heavy ion collisions.     

Properties of baryonic,electric and strangeness chemical potentials and some of their consequences in relativistic heavy ion collisions

Analytic expressions are given for the baryonic, electric and strangeness chemical potentials which explicitly show the importance of various terms. Simple scaling relations connecting these chemical potentials are found. Applications to particle ratios and to fluctuations and related thermal properties such as the isothermal compressibility κT${\kappa }_T$ are illustrated. A possible divergence of κT${\kappa }_T$ is discussed.     

Elliptic flow in an integrated (3+1)d microscopic + macroscopic approach with fluctuating initial conditions

The elliptic flow excitation function calculated in a Boltzmann approach with an intermediate hydrodynamic stage for heavy-ion reactions from GSI-SIS to the highest CERN-SPS energies is discussed in the context of the experimental data. The specific setup with initial conditions and freeze-out from a non-equilibrium transport model allows for a direct comparison between ideal fluid dynamics and hadronic transport simulations. At higher SPS energies, where the pure transport calculation cannot account for the high elliptic flow values, the smaller mean free path in the hydrodynamic evolution leads to higher elliptic flow values. The lower mean free path leads to higher pressure gradients in the early stage and as a consequence to higher elliptic flow values even without a phase transition. Special emphasis is put on the influence of the initial conditions on the results of the hybrid model calculation. Event-by-event fluctuations are directly taken into account via event-wise non-equilibrium initial conditions generated by the primary collisions and string fragmentations in the microscopic UrQMD model. This leads to non-trivial velocity and energy density distributions for the hydrodynamical initial conditions. Due to the more realistic initial conditions and the incorporated hadronic rescattering the results are in line with the experimental data almost over the whole energy range from E _lab=2–160A GeV.     

Differential Directed Flow of K+ Meson within Covariant Kaon Dynamics

The collective flow of positive charged kaons in heavy ion reactions at SIS energy is investigated within the frame of covariant kann dynamics. The theoretical results calculated by using quantum molecular dynamics show that the rapidity distribution of K^＋ mesons is more sensitive to the nuclear equation of state than the differential directed flow. The contribution of various K^＋ production reaction channels to the rapidity distribution of the K^＋ is also analysed in detail. The results indicate that the rapidity distribution of K^＋ mesons is mainly from the contribution of the N-△ and N-N channel. This means that the delta resonance state plays a predominantly important role for the K^＋ subthreshold production.     

Centrality dependence of v 2 in Au + Au at \sqrt{s_{NN}}=200 GeV

One of the most striking results is the large elliptic flow (v ₂) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations for p _T<1 GeV/c, and by parton coalescence/recombination picture for p _T=2–6 GeV/c. The systematic error on v ₂ is dominated by so-called “non-flow effects”, which are correlations other than flow, such as resonance decays and jets. It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision dynamics. In this paper, we present the centrality dependence of v ₂ with respect to the first harmonic event plane at ZDC-SMD (v ₂{ZDC-SMD}) in Au + Au collisions at  GeV. A large rapidity gap (|Δη|>6) between midrapidity and the ZDC-SMD could enable us to minimize possible non-flow contributions. We compare the results of v ₂{ZDC-SMD} with v ₂{BBC}, which is measured by event plane determined at |η|=3.1–3.9. Possible non-flow contributions in those results will be discussed.     

Detection of source inhomogeneity through event-by-event two-pion Bose–Einstein correlations

We develop a method for detecting the inhomogeneity of the pion-emitting sources produced in ultra-relativistic heavy ion collisions, through event-by-event two-pion Bose–Einstein correlations. The root-mean-square of the error-inverse-weighted fluctuations between the two-pion correlation functions of single and mixed events are useful observables for the detection. By investigating the root-mean-square of the weighted fluctuations for different impact parameter regions people may hopefully determine the inhomogeneity of the particle-emitting in the coming Large Hadron Collider (LHC) heavy ion experiments.