Recent results from the Relativistic Heavy Ion Collider (RHIC)

The most recent physics results obtained at the Relativistic Heavy Ion Collider (RHIC) are surveyed. The survey is devoted to considering p + p, Cu + Cu, and Au + Au systems of colliding nuclei at c.m. energies of √ ^s NN = 200, 62.4, and 22.4 GeV. The results obtained within the first years of collider operation are discussed. New data on the production of high-transverse-momentum particles are presented. Manifestations of collective flows, such as the radial and elliptic flows, as well as the formation of a shock wave and a ridge, are considered. The results concerning heavy-quark production are also discussed.     

Matter formed at the BNL Relativistic Heavy Ion Collider

We suggest that the "new form of matter" found just above T(c) by the Relativistic Heavy Ion Collider is made up of tightly bound quark-antiquark pairs, essentially 32 chirally restored (more precisely, nearly massless) mesons of the quantum numbers of pi, sigma, rho, and a1. Taking the results of lattice gauge simulations (LGS) for the color Coulomb potential from the work of the Bielefeld group and feeding this into a relativistic two-body code, after modifying the heavy-quark lattice results so as to include the velocity-velocity interaction, all ground-state eigenvalues of the 32 mesons go to zero at T(c) just as they do from below T(c) as predicted by the vector manifestation of hidden local symmetry. This could explain the rapid rise in entropy up to T(c) found in LGS calculations. We argue that how the dynamics work can be understood from the behavior of the hard and soft glue.     

Evaluating results from the Relativistic Heavy Ion Collider with perturbative QCD and hydrodynamics

We review the basic concepts of perturbative quantum chromodynamics (QCD) and relativistic hydrodynamics, and their applications to hadron production in high energy nuclear collisions. We discuss results from the Relativistic Heavy Ion Collider (RHIC) in light of these theoretical approaches. Perturbative QCD and hydrodynamics together explain a large amount of experimental data gathered during the first decade of RHIC running, although some questions remain open. We focus primarily on practical aspects of the calculations, covering basic topics like perturbation theory, initial state nuclear effects, jet quenching models, ideal hydrodynamics, dissipative corrections, freeze-out and initial conditions. We conclude by comparing key results from RHIC to calculations.     

相对论重离子碰撞中的重味产生

重味粒子是新的物质形态——夸克胶子等离子体的敏感探针。 利用相对论流体力学描述夸克胶子等离子体的时空演化, 采用输运方程模拟重味粒子在夸克胶子等离子体中的运动, 既考虑重味粒子的热胶子离解, 也通过细致平衡原理包含重味粒子在热密媒质中的重产生。 正是由于离解与重产生之间的竞争以及竞争对于碰撞能量、 横动量和快度的依赖性, 自然解释了在RHIC能区的J/ψ疑难, 预言了在LHC能区由于重产生取得主导地位, J/ψ的核修正因子在中心和半中心碰撞中将随着参与反应核子数的增大而升高, 同时其平均横动量会受到强烈的压低。 Heavy quarkonium is a sensitive signature of the new state of matter-quark gluon plasma produced in high energy nuclear collisions. We describe the space time evolution of the quark gluon plasma by relativistic hydrodynamic equations and the quarkonium motion by transport equation. We found that the competition between the gluon dissociation and regeneration can explain naturally the J/ψ puzzles at RHIC energy. We predict the increase of the nuclear modification factor in semi central and central collisions and the related transverse momentum suppression at LHC energy.     

Chiral electric field in relativistic heavy-ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

It has been proposed that electric fields may lead to chiral separation in quark-gluon plasma(QGP).This is called the chiral electric separation effect.The strong electromagnetic field and the QCD vacuum can both be completely produced in off-central nuclear-nuclear collision.We use the Woods-Saxon nucleon distribution to calculate the electric field distributions of off-central collisions.The chiral electric field spatial distribution at Relativistic Heavy-Ion Collider(RHIC) and Large Hadron Collider(LHC) energy regions are systematically studied in this paper.The dependence of the electric field produced by the thermal quark in the central position with different impact parameters on the proper time with different collision energies in the RHIC and LHC energy regions are studied in this paper.     

Evidence for higher order QED effects in e+ e- pair production at the BNL Relativistic Heavy Ion Collider

A new lowest order QED calculation for BNL Relativistic Heavy-Ion Collider e+ e- pair production has been carried out with a phenomenological treatment of the Coulomb dissociation of the heavy-ion nuclei observed in the STAR ZDC triggers. The lowest order QED result for the experimental acceptance is nearly 2 standard deviations larger than the STAR data. A corresponding higher-order QED calculation is consistent with the data.     

相对论重离子碰撞与夸克物质

介绍了相对论重离子碰撞与夸克物质研究领域的有关最新进展.讨论了QCD热力学与量子输运理论,对于与QCD相变紧密联系的几个热点问题作了评述,最后分析了该研究领域在近期发展前景.     

Relativistic Heavy Ion Collisions and Quark Matter

The recent progress in the field of relahvistic heavy ion collisions and quark matter is reviewed. Especially, the QCD thermodynamics, quantum transport theory, and some hot topics related to the QCD phase transitions are analyzed in detail. The outlook for thes field is also briefly discussed.     

Heavy ions with the Large Hadron Collider and the ALICE detector

The Large Hadron Collider (LHC) under construction at CERN is also planned as a heavy ion collider with lead ions colliding at an energy of 2.7+2.7 ATeV. This corresponds to collisions of matter with cosmic rays of the utmost energies observed so far promising the study of new and exciting aspects of physics. Minor improvements of the newly commissioned lead ion source at the CERN SPS are necessary in order to provide a luminosity of L=2×10²⁷ cm^?2s^?1. The detector ALICE has been chosen as the third detector for the LHC and will be dedicated to the physics of these nuclear collisions and also to the large cross section physics in p+p collisions.     

相对论重离子碰撞中Λ粒子产生和Λ/p比率

利用强子输运–弦碎裂模型研究了200A GeV重离子碰撞中Λ多重产生和Λ/p比率.研究了它们随反应系统大小和碰撞中心度的变化.研究表明Λ和p多重数都随反应系统增大和随碰撞中心度提高而增大,但它们的比率基本保持不变.Λ的湮没截面大小变化对Λ的多重数产生有一定影响,但对Λ/p比率影响不大.结果很好地再现了pp反应中Λ/p比率.并获得这一比率在AA反应中是pp反应中的3—5倍.     

相对论重离子反应的热化过程

本文从相对论BUU理论出发研究了1GeV/n能区重离子反应全局(global)和局域(local)平衡性质,计算表明在该能区平均场对反应动力学过程仍有相当的作用;对有限核系统的反应动力学过程的时间演化的研究表明,有限核系统无论全局的还是局域的平衡均未能达到完全平衡,因而对有限核系统重离子反应基于完全热平衡概念的适用性值得怀疑.     

Emission of Neutral Pions with High Transverse Momenta in A-A and p-p Collisions at Energies Available at the BNL Relativistic Heavy Ion Collider

Invariant neutral pion （π^0） yields in Au-Au and Cu-Cu collisions and invariant π^0 cross sections in p-p collisions are studied in the framework of a two-cylinder model. The considered distributions of neutral pions at the maximum energy of the relativistic heavy ion eollider （RFIIC） have a tail part in the region of high transverse momentum. A two-component distribution based upon the two-cylinder model is used to describe the experimental data of the PHENIX collaboration.     

Energy dependence of directed flow over a wide range of pseudorapidity in Au + Au collisions at the BNL Relativistic Heavy Ion Collider

We report on measurements of directed flow as a function of pseudorapidity in Au + Au collisions at energies of square root of SNN = 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at the BNL Relativistic Heavy Ion Collider. These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.     

Estimation on Local Energy Density in Relativistic Heavy Ion Collisions

Energy density for the central region in relativistic heavy ion collisionscan be estimated via the pseudora-pidity distribution of transverse energy. The way to estimate the local energy density for the centralregion in relativisticheavyion collisions is proposed, in which only final state particles emitted from the same source are included. Thcarrived energy density in NA49 experiments is about 1.03 GeV/fm3.     

相对论重离子碰撞中的线性背景与非线性效应

系统分析了p-A,¹⁶O-A和³²S-A过程快度分布的靶核依赖性.指出:将核子-核,核-核碰撞看成核子-核子碰撞的线性叠加的几何模型只能得到靶核指数α(η) 0.4.靶核碎裂区α(η)→1的实验数据表明,目前能量下的高能重离子碰撞中,非线性效应已不可忽略.流体动力学模型计算的结果能很好地描述不同射弹过程的靶核依赖性.