Directed and elliptic flow in 197Au+197Au at intermediate energies

Directed and elliptic flow for the ¹⁹⁷Au+¹⁹⁷Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ _NN and demonstrate the importance of angular momentum conservation in transport codes at low energies.     

Eccentricity and elliptic flow at fixed centrality in Au+Au collisions at sNN=200 GeV in AMPT model

In this paper, elliptic flow is studied at fixed centrality in Au+Au collision at √s_NN=200 GeV in the AMPT model. It is observed that with the participant increasing, elliptic flow has an increase or a decrease at different fixed impact parameter, but it does not have a trivial fluctuation. It is analyzed that the initial space anisotropy dominates the participant dependence of elliptic flow in near-central collisions(b=5 fm) and mid-central collisions(b=8 fm), while the interaction between particles can mainly answer for the behavior of elliptic flow with participant in peripheral collisions (b=12 fm). To distinguish the pure geometrical effect, elliptic flow scaled by initial eccentricity is studied. It is found that the ratio v₂/ε increases with participant and reaches a saturation when the participant is large enough, indicating that the collision system may reach the local equilibrium.     

Impact parameter dependence of the scaling of anisotropic flowsin intermediate energy heavy-ion collisions

The scaling behaviors of anisotropic flows of light charged particles are studied for 25 MeV/u ⁴⁰Ca+⁴⁰Ca collisions at different impact parameters by the isospin-dependent quantum molecular dynamics model. The nucleon-number scaling of elliptic flow exists and the scaling of the ratios of v₄/v₂² and v₃/(v₁v₂) is applicable to collisions at almost all impact parameters except for peripheral collisions.     

RHIC-STAR重离子碰撞实验中可鉴别粒子的集体流研究

本文总结了RHIC-STAR重离子碰撞实验中近年来重要的空间各向异性流的结果。主要包括最高能量重离子碰撞中多重奇异及含粲夸克粒子椭圆流的结果和RHIC能量扫描计划BES-I中椭圆流和直接流的结果,其中金金碰撞54.4和27 GeV是最新测量结果。我们发现新碰撞能量点的直接流符合碰撞能量依赖的总体趋势;椭圆流符合组分夸克标度性,这表明54.4和27 GeV的金金碰撞中形成了部分子层次的集体运动。同时展望了未来能量扫描实验的计划以及与之对应的空间各向异性流的研究重点。     

利用椭圆流和轻带电粒子产额比探测对称能（英文）

基于最近更新的极端相对论量子分子动力学模型,研究了197Au+197Au产生的中子和氢同位素的横动量依赖的椭圆流和轻带电粒子的产额比。发现中子和氢同位素的椭圆流之比vn H2/v2敏感于对称能的高密行为,而3H和3He的产额比敏感于对称能的低密行为。通过比较FOPI/LAND和FOPI合作组的最新实验数据与模型模拟的结果,发现接近线性对称能的Skyrme参数给出的结果能与这两个实验值都符合。     

Possible Mechanisms of Ternary Fission in the 197Au+197Au System at 15 A MeV

Ternary fission in ^197Au＋^197Au collisions at 15 A MeV is investigated by using the improved quantum molecular dynamical （ImQMD） model. The experimental mass distributions for each of the three fragments are reproduced for the first time without any freely adjusting parameters. The mechanisms of ternary fission in central and semicentral collisions are dynamically studied. In direct prolate ternary fission, two necks are found to be formed almost simultaneously and rupture sequentially in a very short time interval. Direct oblate ternary fission is a very rare fission event, in which three necks are formed and rupture simultaneously, forming three equally sized fragments along space-symmetric directions in the reaction plane. In sequential ternary fission a binary division is followed by another binary fission event after hundreds of fm/c.     

Azimuthal correlations between directed and elliptic flow in heavy ion collisions

A method for investigating the azimuthal correlations between directed and elliptic flow in heavy ion collisions is described. The transverse anisotropy of particle emission at AGS energies is investigated within the RQMD model. It is found that the azimuthal correlations between directed and elliptic flow are sensitive to the incident energy and impact parameter. The fluctuations in the     

中能重离子反应中的在平面流和椭圆流

利用同位旋相关的量子分子动力学模型研究了⁴⁰Ca+⁴⁰Ca系统在能量从30MeV/u到150MeV/u的在平面流和椭圆流.发现随着入射能量的增加,在平面流出现从负到正的跃迁,而椭圆流则随入射能量的增大而减少并且出现从正到负的跃迁.椭圆流和在平面流对于入射能量和碰撞参数较为敏感,相反对于对称能和核态方程却不太敏感.最后对于不同质量的碎块的依赖性关系我们还作了进一步仔细的研究.     

Azimuthal correlations between directed and elliptic flow in heavy ion collisions

A method for investigating the azimuthal correlations between directed and elliptic flow in heavy ion collisions is described.The transverse anisotropy of particle emission at AGS energies is investigated within the RQMD model.It is found that the azimuthal correlations between directed and elliptic flow are sensitive to the incident energy and impact parameter.The fluctuations in the initial stage and dynamical evolution of heavy ion collisions are not negligible.     

The effect of Lorentz-like force on collective flows of <Emphasis Type="Italic">K</Emphasis><Superscript>+</Superscript> in Au+Au collisions at 1.5 GeV/nucleon

Producing kaon mesons in heavy-ion collisions at beam energies below their threshold energy is an important way to investigate the properties of dense nuclear matter. In this study, based on the newly updated version of the ultrarelativistic quantum molecular dynamics model, we introduce the kaon-nucleon (KN) potential, including both the scalar and vector (also dubbed Lorentz-like) aspects. We revisit the influence of the KN potential on the collective flow of K⁺ mesons produced in Au+Au collisions at E_lab = 1.5 GeV/nucleon and find that the contribution of the newly included Lorentz-like force is very important, particulary for describing the directed flow of K⁺. Finally, the corresponding KaoS data of both directed and elliptic flows can be simultaneously reproduced well.     

NeXSPheRIO results on elliptic flow and directed flow for Au+Au and Cu+Cu collisions at RHIC

Hydrodynamics has been rather successful at describing results obtained in relativistic nuclear collisions at RHIC. Here we show results obtained with NeXSPheRIO on Au+Au collisions and the less studied Cu+Cu collisions. We study elliptic flow and its connection with eccentricity suggested by PHOBOS, as well as present elliptic flow fluctuations. We also show results for directed flow and compare with PHOBOS and STAR data.     

Directed and elliptic flows in 40Ca + 40Ca and 112Sn + 112Sn collisions

The directed and elliptic flows for different light particles and fragments in collisions of ⁴⁰Ca + ⁴⁰Ca and ¹¹²Sn + ¹¹²Sn at energies from 30MeV/nucleon to 100MeV/nucleon were studied in the isospin-dependent quantum molecule dynamics model (IQMD). With increasing incident energy, the directed flow rises from negative to positive, while the elliptic flow decreases with increasing the incident energies. The directed flow for the ⁴⁰Ca + ⁴⁰Ca system is not sensitive to the nuclear equation of states (EOS), but the directed flow for the ¹¹²Sn + ¹¹²Sn system is sensitive to the EOS. However, the elliptic flows for both ⁴⁰Ca + ⁴⁰Ca and ¹¹²Sn + ¹¹²Sn systems are not sensitive to EOS. A study of the dependence of directed and elliptic flows on the fragment charge (mass) is also performed. Received: 15 March 2002 / Accepted: 14 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: Zhanghy@sinr.ac.cn; Permanent address: Shanghai Institute of Nuclear Research, Chinese Academy of Sciences, P.O. Box 800-204(2), Shanghai 201800, China. Communicated by W. Henning     

Anisotropic flow at RHIC

STAR’s measurement of directed flow for pions,kaons(K 0 S ),protons and anti-protons,for Au+Au collisions at 200 GeV obtained in Run7 are presented,as well as elliptic flow for identified particles measured in Au+Au(Run7) and Cu+Cu(Run5) collisions.It is found that the slope of proton v 1 (y) at midrapidity is extremely small.Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.     

Flow effects in high-energy nucleus collisions with Ag(Br) in emulsion

Various flow phenomena observed by a unique emulsion method are reviewed. The experimental data of the emission of projectile and target fragments and relativistic particles in collisions of 1–160 A GeV/c ¹⁶O, ²²Ne, ²⁸Si, ³²S, ⁸⁴Kr, ¹⁹⁷Au, and ²⁰⁸Pb nuclei with ¹⁰⁸Ag (⁸⁰Br) targets are investigated. The transverse-momentum approach, the flow-angle analysis using principal vectors, the azimuthal correlation functions, the method of azimuthal correlations between charged secondaries, and the method of Fourier expansion of the azimuthal angle distributions are applied. Evidence of the directed flow of spectators has been obtained in the medium-impact nuclear interactions. In azimuthal distributions, with respect to the reaction plane, the signal of the elliptic flow of participants has been observed.     

Application of the Modified BUU Model to Reaction Induced by 16O on 197An at 20MeV≤E/u≤180 MeV:Dependence of the Angalar and Linear Momentum Transfer on Impact Parameter and Energy

The angular and linar momentum transfered to target residue on 20 to 180MeV/u ¹⁶O+¹⁹⁷Au system are calculated with BUU(Boltzmann-Uehling-Uhlenbeck) model in which the angular momentum conservation is added.The dependence of angular and linar momentum on impact parameter and incident energy is discussed.The deviations between calculated values of(1mt) and those from viola system are compared.The results of the simulations suggest that the saturation of angular momentum transfer with incident energy increase mainly comes from the loss of capture ability of the target on projectile.     

Partonic effect on anisotropic flows of Ω baryon for Au+Au at 62.4 and 200 GeV/c

The elliptic flow v₂ and the fourth order anisotropic flow v₄ of (Ω+Ω̄) have been studied in the framework a parton–hadronic transport model, namely a multi-phase transport (AMPT) model, for ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV and 62.4 GeV. The transverse momentum (p_T) and the transverse kinetic energy (m_T-m₀) dependence of v₂ and v₄ are presented. The calculation in the AMPT model seems consistent with the STAR data. The results show that the v₂ of (Ω+Ω̄) in 200 GeV obeys the constituent quark number scaling that has been observed for other mesons and baryons. Comparison of (Ω+Ω̄) elliptic flow v₂ in the default version of AMPT, the melting version of AMPT and the RQMD model calculation, shows that the parton cascade process is important to reproduce the sizeable v₂, and the string melting AMPT model preferably reproduces (Ω+Ω̄) elliptic flow v₂ in ¹⁹⁷Au+¹⁹⁷Au collisions at = 200 GeV. The v₂ of (Ω+Ω̄) in the 62.4 and 200 GeV collisions seem similar, and the p_T dependence of (Ω+Ω̄) baryons’ v₄ in 62.4 GeV and 200 GeV looks also similar in the string melting AMPT model, which indicates that a similar partonic matter phase has been reached in both energies.     

Emission Time Measurements of Light Particles from 40Ar+197Au Collisions in Intermediate Energies

Particle-particle correlation functions have been measured for ⁴⁰Ar+¹⁹⁷Au collisions at E=25 MeV/u.Emission time of light particles has been extracted from correlation functions using the three-body trajectory model.The average emission time varies with the energy of particles. It decreases from about 300 fm/c for low energy particles to about 100fm/c for energetic particles.     

Correlations between emerging alpha-particles and heavy ions in 32S+197 Au collisions

In-plane angular correlations between α-particles and projectile residue nuclei (Z=5?22) emerging from ³²S+¹⁹⁷Au collisions have been measured at 373 MeV incident energy. In the combined Coulomb field of the projectile residue and the target nucleus coincident α-particles are strongly focused into a narrow cone. Model calculations indicate that α-emission originates from the region of the projectile which is facing the target nucleus during the collision.     

Differential neutron-proton squeeze-out

The elliptic flow (squeeze-out) of neutrons, protons and light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable, sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. Preliminary results from a study of the existing FOPI/LAND data for ¹⁹⁷Au + ¹⁹⁷Au collisions at 400 A MeV with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to (ρ/ρ₀)^γ with γ=0.6±0.3.     

The effect of Lorentz-like force on collective flows of K+in Au+Au collisions at 1.5 Ge V/nucleon

Producing kaon mesons in heavy-ion collisions at beam energies below their threshold energy is an important way to investigate the properties of dense nuclear matter. In this study, based on the newly updated version of the ultrarelativistic quantum molecular dynamics model, we introduce the kaon-nucleon(KN) potential, including both the scalar and vector(also dubbed Lorentz-like)aspects. We revisit the influence of the KN potential on the collective flow of K+mesons produced in Au+Au collisions at Elab= 1.5 Ge V/nucleon and find that the contribution of the newly included Lorentz-like force is very important, particulary for describing the directed flow of K+. Finally, the corresponding Kao S data of both directed and elliptic flows can be simultaneously reproduced well.