Wei-Liang Qian

Topology studies of hydrodynamics using two-particle correlation analysis.

The effects of fluctuating initial conditions are studied in the context of relativistic heavy ion collisions where a rapidly evolving system is formed. Two-particle correlation analysis is applied to events generated with the NEXSPHERIO hydrodynamic code, starting with fluctuating nonsmooth initial conditions (IC). The results show that the nonsmoothness in the IC survives the hydroevolution and can be seen as topological features of the angular correlation function of the particles emerging from the evolving system. A long range correlation is observed in the longitudinal direction and in the azimuthal direction a double peak structure is observed in the opposite direction to the trigger particle. This analysis provides clear evidence that these are signatures of the combined effect of tubular structures present in the IC and the proceeding collective dynamics of the hot and dense medium.

A closer look at the influence of tubular initial conditions on two-particle correlations

One of the most striking results in relativistic heavy ion collisions is the existence of some structures in the two-particle correlations [1, 2, 3]. One structure has a long (pseudo)rapidity extent [4] and a narrow azimuthal extent. The other may have a long (pseudo)rapidity extent and has a single or double hump in azimuth. In order that two-particles A and B emitted at some proper time τf.out appear as correlated, the process that correlated them must have occurred[5, 6] at some proper time τ ≤ τf.out exp(−|yA − yB|/2). Therefore, the existence of long range (pseudo)rapidity correlations must be related to early times in the nuclear collisions. These two-particle azimuthal correlations data have motivated many theoretical investigations (for a short critical review see e.g.[7]). In many of these approaches, the mechanism is closely related to jet quenching and the response of the medium to the deposited energy. However, 1) the ridge structure is also seen at low transverse momentum[8, 9]; 2) recent experimental data seem to indicate no correlation between high pt trigger and associated ridge particles [10]. In another class of models, it is suggested that the combined effect of a longitudinal structure in the initial conditions (IC) and transverse expansion is responsible for the ridge [5, 6, 11]. In this line, we have studied the two-particle correlation by using a hydrodynamic code NEXSPheRIO[12]. Both the near-side and double-hump away-side structures were reproduced. In this work, we discuss how exactly these structures appear as well as present new results.In a recent paper, the hydrodynamic code NEXSPheRIO was used in conjunction with STAR analysis methods to study two-particle correlations as a function of Δη and Δ. The various structures observed in the data were reproduced. In this work, we discuss the origin of these structures as well as present new results.

Decomposition of fluctuating initial conditions and flow harmonics

Collective flow observed in heavy-ion collisions is largely attributed to initial geometrical fluctuations, and it is the hydrodynamic evolution of the system that transforms those initial spatial irregularities into final state momentum anisotropies. Cumulant analysis provides a mathematical tool to decompose those initial fluctuations in terms of radial and azimuthal components. It is usually thought that a specified order of azimuthal cumulant, for the most part, linearly produces flow harmonics of the same order. In this work, by considering the most central collisions (0%–5%), we carry out a systematic study on the connection between cumulants and flow harmonics using a hydrodynamic code called NeXSPheRIO. We conduct three types of calculation, by explicitly decomposing the initial conditions into components corresponding to a given eccentricity and studying the out-coming flow through hydrodynamic evolution. It is found that for initial conditions deviating significantly from Gaussian, such as those from NeXuS, the linearity between eccentricities and flow harmonics partially breaks down. Combined with the effect of coupling between cumulants of different orders, it causes the production of extra flow harmonics of higher orders. We argue that these results can be seen as a natural consequence of the non-linear nature of hydrodynamics, and they can be understood intuitively in terms of the peripheral-tube model.

Isospin dependence of liquid–gas phase transition in hot asymmetric nuclear matter

Abstract By using the Furnstahl, Serot and Tangs model, the effect of density dependence of the effective nucleon–nucleon– ρ -meson (NN ρ ) coupling on the liquid–gas phase transition in hot asymmetric nuclear matter is investigated. A limit pressure p lim has been found. We found that the liquid–gas phase transition cannot take place if p > p lim . The binodal surface for density dependent NN ρ coupling situation is addressed.

NeXSPheRIO results on elliptic-flow fluctuations at RHIC

By using the NeXSPheRIO code, we study the elliptic-flow fluctuations in Au + Au collisions at 200 A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudorapidity and the transverse-momentum distributions, reasonable agreement of 〈v2〉 with data is obtained, both as function of pseudorapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data on experiments.

Temporal evolution of tubular initial conditions and their influence on two-particle correlations in relativistic nuclear collisions

Abstract Relativistic nuclear collisions data on two-particle correlations exhibit structures as function of relative azimuthal angle and rapidity. A unified description of these near-side and away-side structures is proposed for low to moderate transverse momentum. It is based on the combined effect of tubular initial conditions and hydrodynamical expansion. Contrary to expectations, the hydrodynamics solution shows that the high-energy density tubes (leftover from the initial particle interactions) give rise to particle emission in two directions and this is what leads to the various structures. This description is sensitive to some of the initial tube parameters and may provide a probe of the strong interaction. This explanation is compared with an alternative one where some triangularity in the initial conditions is assumed. A possible experimental test is suggested.

Origin of trigger-angle dependence of di-hadron correlations

The STAR Collaboration reported measurements of di-hadron azimuthal correlation in medium-central Au+Au collisions at 200 A

Influence of density dependence of NNρ coupling on the liquid-gas phase transition in warm asymmetric nuclear matter

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Numerical study of the density of states for the bag model

GeV, where the data are presented as a function of the trigger particles azimuthal angle relative to the event plane

EFFECT OF CHEMICAL FREEZE OUT ON IDENTIFIED PARTICLE SPECTRA AT 200 AGeV Au-Au COLLISIONS AT RHIC USING SPheRIO

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