超相对论Au+Au碰撞中椭圆流的时间依赖

用相对论量子分子动力学(RQMD)模型模拟了质心系束能量为s_NN=200GeV的Au+Au非对心碰撞, 研究了椭圆流对末态粒子冻出时间的关系. 研究了在不同的阶段, 椭圆流对末态粒子位置的关系. 结果表明椭圆流随冻出时间的单调递减, 椭圆流对横向半径的关系随冻出时间发生变化. 用压力梯度对所得结果进行了分析. 径向速度用来表征压力梯度.     

Scaling properties of azimuthal anisotropy in Au+Au and Cu+Cu Collisions at sqrt[s NN]=200 GeV

Differential measurements of elliptic flow (v2) for Au+Au and Cu+Cu collisions at sqrt[sNN]=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v2 with eccentricity, system size, and transverse kinetic energy (KE T). For KE T identical with mT-m up to approximately 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KE T mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v2 for both mesons and baryons over the full KE T range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KE T, rather than transverse momentum.     

Partonic Flow and phi-Meson production in Au+Au collisions at sqrt radical sNN = 200 GeV

We present first measurements of the phi-meson elliptic flow (v2(pT)) and high-statistics pT distributions for different centralities from radical sNN=200 GeV Au+Au collisions at RHIC. In minimum bias collisions the v2 of the phi meson is consistent with the trend observed for mesons. The ratio of the yields of the Omega to those of the phi as a function of transverse momentum is consistent with a model based on the recombination of thermal s quarks up to pT approximately 4 GeV/c, but disagrees at higher momenta. The nuclear modification factor (R CP) of phi follows the trend observed in the K S 0 mesons rather than in Lambda baryons, supporting baryon-meson scaling. These data are consistent with phi mesons in central Au+Au collisions being created via coalescence of thermalized s quarks and the formation of a hot and dense matter with partonic collectivity at RHIC.     

Spectra,elliptic flow and azimuthally sensitive HBT radii from the Buda-Lund model for $ \sqrt{{s_{NN}}}$ = 200 GeV Au + Au collisions

We present calculations of elliptic flow and azimuthal dependence of correlation radii in the ellipsoidally symmetric generalization of the Buda-Lund hydrodynamic model of hadron production in high-energy nuclear collisions. We compare them to data from RHIC by simultaneous fits to azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX in Au + Au reactions at center-of-mass energy of 200 AGeV. STAR data were used for azimuthally sensitive two-particle correlation function radii and for the transverse momentum dependence of the elliptic flow parameter v ₂. We have found that the transverse flow is faster in the reaction plane than out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane. The model parameters extracted from the fits are shown and discussed.     

Effects of mean-field and softening of equation of state on elliptic flow in Au+Au collisions at (~SNN)~(1/2)=5 GeV from the JAM model

We perform a systematic study of elliptic flow(v_2) in Au+Au collisions at(~SNN)~(1/2) = 5 GeV by using a microscopic transport model, JAM. The centrality, pseudorapidity, transverse momentum and beam energy dependence of v_2 for charged as well as identified hadrons are studied. We investigate the effects of both the hadronic mean-field and the softening of equation of state(EoS) on elliptic flow. The softening of the EoS is realized by imposing attractive orbits in two body scattering, which can reduce the pressure of the system. We found that the softening of the EoS leads to the enhancement of v_2, while the hadronic mean-field suppresses v_2 relative to the cascade mode. It indicates that elliptic flow at high baryon density regions is highly sensitive to the EoS and the enhancement of v_2 may probe the signature of a first-order phase transition in heavy-ion collisions at beam energies of a strong baryon stopping region.     

Elliptic flow at SPS and RHIC: from kinetic transport to hydrodynamics

Anisotropic transverse flow is studied in Pb+Pb and Au+Au collisions at SPS and RHIC energies. The centrality and transverse momentum dependence at midrapidity of the elliptic flow coefficient v₂ is calculated in the hydrodynamic and low density limits. Hydrodynamics is found to agree well with the RHIC data for semicentral collisions up to transverse momenta of 1–1.5 GeV/c, but it considerably overestimates the measured elliptic flow at SPS energies. The low density limit LDL is inconsistent with the measured magnitude of v₂ at RHIC energies and with the shape of its p_t-dependence at both RHIC and SPS energies. The success of the hydrodynamic model points to very rapid thermalization in Au+Au collisions at RHIC and provides a serious challenge for kinetic approaches based on classical scattering of on-shell particles.     

在RHIC-PHENIX中、(√SNN)=200GeV Au+Au碰撞中直接光子的椭圆流测量

Azimuthal anisotropy of direct photon is measured in (√SNN)=200GeV Au Au collisions at RHICPHENIX. Direct photon is one of the most effective probes to study properties of hot dence medium at initial state (also QGP state) of heavy ion collisions because photons almost do not interact strongly with any other particles caused by its long mean free path and they keep their conditions when they are created. Within statistical and systematic errors, the elliptic flow parameter (v2) of direct photon is consistent with zero.Direct photon v2 is estimated by hadron decay photon contamination are subtracted from inclusive photon v2 in intermediate to high transverse momentum (pT) region (0 to 10GeV/c) for 3 centrality selections (20% steps) and minimum bias.     

Influence of shear viscosity of quark-gluon plasma on elliptic flow in ultrarelativistic heavy-ion collisions

We investigate the influence of a temperature-dependent shear viscosity over entropy density ratio η/s on the transverse momentum spectra and elliptic flow of hadrons in ultrarelativistic heavy-ion collisions. We find that the elliptic flow in √S(NN)=200 GeV Au+Au collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the viscosity of the quark-gluon plasma (QGP). At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity.     

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.     

部分子相互作用与(S_(NN))~(1/2)=130GeV Au-Au碰撞中两粒子的横向动量关联(英文)

采用蒙特卡罗模型AMPT 究了(S_(NN))~(1/2)=130GeV Au Au碰撞中部分子相互作用对两粒子横向动量关联的影响,结果表明部分子相互作用对两粒子的横向动量关联有重要的贡献．还计算了AMPT模型中(S_(NN))~(1/2)=130GeV Au Au碰撞的两粒子横向动量关联与碰撞对心性的依赖关系并与来自STAR的实验数据进行了比较,发现AMPT的理论预言很好地符合实验数据．     

Space-momentum correlations in 8 AGeV Au+Au collisions

Within the RQMD model, space-momentum correlations, i.e. the correlations between final momentum anisotropy and initial eccentricity, are studied for 8 AGeV Au+Au events classified according to the multi-particle azimuthal correlations. The results show that the final elliptic flow fluctuations depend on the initial collision geometry. There are clear space-momentum correlations for nucleons during the whole dynamical evolution of the collisions.     

Space-momentum correlations in 8 AGeV Au+Au collisions

Within the RQMD model, space-momentum correlations, i.e. the correlations between final momentum anisotropy and initial eccentricity, are studied for 8 AGeV Au＋Au events classified according to the multi-particle azimuthal correlations. The results show that the final elliptic flow fluctuations depend on the initial collision geometry. There are clear space-momentum correlations for nucleons during the whole dynamical evolution of the collisions.     

Saturation of azimuthal anisotropy in Au + Au collisions at (square root)s(NN) = 62-200 GeV

New measurements are presented for charged hadron azimuthal correlations at midrapidity in Au+Au collisions at (square root)s(NN) = 62.4 and 200 GeV. They are compared to earlier measurements obtained at (square root)s(NN) = 130 GeV and in Pb + Pb collisions at (square root)s(NN) = 17.2 GeV. Sizeable anisotropies are observed with centrality and transverse momentum (pT) dependence characteristic of elliptic flow (upsilon2). For a broad range of centralities, the observed magnitudes and trends of the differential anisotropy, upsilon2(pT), change very little over the collision energy range (square root)s(NN) = 62-200 GeV, indicating saturation of the excitation function for upsilon2 at these energies. Such a saturation may be indicative of the dominance of a very soft equation of state for (square root)s(NN) approximately 60-200 GeV.     

在RHIC-PHENIX中(s_(NN))~(1/2)=200GeV Au Au碰撞中直接光子的椭圆流测量(英文)

Azimuthal anisotropy of direct photon is measured in S_(NN)~(1/2)=200GeV Au Au collisions at RHIC- PHENIX.Direct photon is one of the most effective probes to study properties of hot dence medium at initial state(also QGP state)of heavy ion collisions because photons almost do not interact strongly with any other particles caused by its long mean free path and they keep their conditions when they axe created.Within statistical and systematic errors,the elliptic flow parameter(v_2)of direct photon is consistent with zero. Direct photon v_2 is estimated by hadron decay photon contamination are subtracted from inclusive photon v_2 in intermediate to high transverse momentum(p_T)region(0 to 10GeV/c)for 3 centrality selections(20% steps)and minimum bias.     

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.     

Elliptic flow of thermal photons in relativistic nuclear collisions

We predict the transverse momentum (p(T)) dependence of elliptic flow of thermal photons for Au + Au collisions at the BNL Relativistic Heavy Ion Collider. We model the system hydrodynamically, with a thermalized quark-gluon plasma at early times followed by hadronization and decoupling. Photons are emitted throughout the expansion history. Contrary to hadron elliptic flow, which increases monotonically with p(T), the elliptic flow nu2(p(T)) of thermal photons is predicted to first rise and then fall again. Photon elliptic flow at high p(T) reflects the quark momentum anisotropy at early times when it is small, while at low p(T) it mirrors the large pion momentum anisotropy during the late hadronic emission stage. An interesting structure is predicted at intermediate p(T) approximately 0.4 GeV/c, where photon elliptic flow reflects the momenta and the (compared to pions) reduced nu2 of heavy vector mesons in the late hadronic phase.     

Azimuthal anisotropy and correlations at large transverse momenta in p + p and Au + Au collisions at square root sNN=200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au + Au collisions at square root s(NN)=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au + Au collisions to those in p + p at the same energy. The elliptic anisotropy v(2) is found to reach its maximum at p(t) approximately 3 GeV/c, then decrease slowly and remain significant up to p(t) approximately 7-10 GeV/c. Stronger suppression is found in the back-to-back high-p(t) particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v(2) at intermediate p(t) is compared to simple models based on jet quenching.     

Flow measurements via two-particle azimuthal correlations in Au + Au collisions at sqrt [s(NN)]=130 GeV

Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au+Au collisions at the Relativistic Heavy Ion Collider (sqrt [s(NN)]=130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (v2) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p(T). A breakdown of this epsilon scaling is observed for charged hadrons with pT >1.0 GeV/c.     

Elliptic flow for phi mesons and (anti)deuterons in Au+Au collisions at square root of sNN=200 GeV

Differential elliptic flow (v(2)) for phi mesons and (anti)deuterons (d)d is measured for Au+Au collisions at square root of sNN=200 GeV. The v(2) for phi mesons follows the trend of lighter pi+/- and K+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v(2) values for (d)d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v(2) per constituent quark for baryons and mesons suggests that partonic collectivity dominates the transverse expansion dynamics.     

RHIC能区Au+Au碰撞中HBT关联参数分析

利用相对论量子分子动力学模型RQMD,对RHIC能区s=200GeV/u Au+Au碰撞进行了2π干涉学分析,并讨论了HBT半径参数对横动量的依赖关系.研究表明,两粒子关联函数能够给出碰撞源在冻结时刻的时空拓扑信息,HBT半径参数能够较好地反映源的尺度和形状,但其对横动量的依赖关系并不能直接反映源的压缩性质,而是对粒子产生时源的空间–动量关联程度更为敏感.