统一流体力学模型与BNL-RHIC低能量区重离子碰撞中的赝快度分布

重离子碰撞产生的高温高密度物质假设按照统一流体力学模型的规律做时空演化,并最终经由一固有时为Tau_FO的类时超曲面冻析为带电粒子。统一流体力学模型是一种将Landau与Hwa-Bjorken两著名流体力学模型结合在一起的模型,是一种少有的可精确求解的理论之一。本文的研究表明:BNL-RHIC低能量区重离子碰撞中带电粒子的赝快度分布可由统一流体力学模型很好地描述。 这与高能区的情况不同,在那里,除了流体外,还需考虑带头粒子的贡献。The hot and dense matter created in heavy ion collisions is supposed to have spatiotemporal evolution according to unified hydro model, and finally freeze out into the charged particles via a space-like hypersurface with a proper time Tau_FO . The unified hydro model is a model which integrates Landau and Hwa-Bjorken two famous hydro models together. It is one of few hydro models which can solved exactly. Shown from the investigations in this paper, the pseudorapidity distribution of charged particles in heavy ion collisions at low BNL-RHIC energy region can be well described by unified hydro model. This is different from that at high nergy region, where, apart from fluid, the contribution from leading particles should be taken into account.     

高能重离子碰撞实验中的软物理研究现状

高能重离子碰撞实验中的软物理研究能够帮助我们清楚认识系统的集体演化过程,并且有助于理解碰撞产生的热密系统的性质。本文介绍了高能重离子碰撞实验中软物理的研究现状及其新近取得的实验成果,包括七部分内容:1)高能重离子碰撞简介;2)碰撞几何方面的研究现状;3)粒子产生方面的研究现状;4)关联与起伏方面的研究现状;5)集体膨胀方面的研究现状;6)强子化方面的研究现状;7)LHC/ALICE实验上的软物理预期。最后,本文对高能重离子碰撞实验中的软物理研究现状进行总结。     

高能重离子碰撞实验中的软物理研究现状

高能重离子碰撞实验中的软物理研究能够帮助我们清楚认识系统的集体演化过程,并且有助于理解碰撞产生的热密系统的性质.本文介绍了高能重离子碰撞实验中软物理的研究现状及其新近取得的实验成果,包括七部分内容:1)高能重离子碰撞简介;2)碰撞几何方面的研究现状;3)粒子产生方面的研究现状;4)关联与起伏方面的研究现状;5)集体膨胀方面的研究现状;6)强子化方面的研究现状,7)LHC/ALICE实验上的软物理预期.最后,本文对高能重离子碰撞实验中的软物理研究现状进行总结.     

高能重离子碰撞中相对论α粒子的双温度发射

本工作利用核乳胶作为靶和探测器, 研究了入射能量超过1A GeV的重离子同乳胶核相互作用时α碎片的发射. 实验测量结果的分析表明, 在高能重离子碰撞过程中, 相对论α粒子的横动量分布给出一个"双有效温度"的特征. 这个特征可能成为判断出现由强子物质向夸克物质相变的一种新的信号.     

新书介绍《高能重离子碰撞导论》

高能重离子碰撞是 2 0世纪 70年代以来形成的一个新的研究领域 ,其目的是研究在相对论和极端相对论能量下 ,由核 -核碰撞所产生的极端高温、高密度的核物质的性质 ,探测新的核物质相。这种研究对人们了解物质更深层次的性质 ,对于粒子物理、核物理和有关宇宙形成及演化的研究都有非常重要的意义。黄卓然 (Ｃｈｅｎｋ -ＹｉｎＷｏｎｇ)先生所著的《Ｉｎｔｒｏ ｄｕｃｔｉｏｎｔｏＨｉｇｈＥｎｅｒｇｙＨｅａｖｙ -ＩｏｎＣｏｌｌｉｓｉｏｎｓ》一书 1994年由新加坡世界科学出版公司出版。哈尔滨工业大学张卫宁教授的中文译本亦于 2 0 0 2年 1…     

核物质的新型态——夸克物质和相对论重离子碰撞

本文简要地介绍了近年来国际上通过高能重离子(相对论重离子)碰撞,探索产生夸克胶子等离子体(QGP)的进展情况。首先从理论上简单论证利用高能重离子碰撞产生QGP 的相变条件、核相图和产生QGP 的时空演化过程,同时还介绍了近年来CERN 和BNL 两个实验室在探索产生QGP 的实验进展情况。随后,着重介绍了高能重离子碰撞的末态观测量和QGP 的形成信号。     

修正的Landau 流体力学模型与Cu+Cu 碰撞末态带电粒子赝快度分布

采用修正的Landau 流体力学模型,并考虑到带头粒子效应,对高能重离子碰撞末态带电粒子的赝快度分布进行了讨论。指出:带头粒子的快度分布应为高斯形式,其正规化常数为参与者数。研究表明:流体力学模型本身与BNL-RHIC-PHOBOS 合作组在(NN)½ =200 GeV 的Cu+Cu 碰撞中的实验测量符合得不是很好,只有将参与者的贡献包括在内,实验结果才能得到很好的描述。By using the revised Landau hydrodynamic model and taking into account the effect of leading particles, we discussed the pseudorapidity distributions of final charged particles in high energy heavy ion collisions. We argued that the rapidity distributions of leading particles have the Gaussian form with the normalization constant being equal to the number of participants. The investigations show that the results from the hydrodynamic model alone are not consistent with the experimental data carried out by BNL-RHIC-PHOBOS Collaboration in Cu+Cu collisions at (NN)½ = 200 GeV. Only after the contributions from leading particles are included, can the experimental measurements be described well.     

超高速碰撞产生等离子体云的粒子能量时空分布

为了研究超高速碰撞产生等离子体的粒子能量对航天器电路中元器件的毁伤,获得超高速碰撞产生等离子体粒子能量的时空分布特性是十分必要的。基于超高速碰撞产生稀薄等离子体中带电粒子的运动速度、等离子体的扩散特点,推导出等离子体的粒子能量密度与带电粒子密度及带电粒子运动速度的关系式。进而通过对超高速碰撞2024-T4铝靶实验采集的原始数据分析,利用Matlab编程得到了超高速碰撞2024-T4铝靶产生膨胀等离子体云物理过程中,等离子体的粒子能量密度与带电粒子持续时间及被测点到碰撞点距离的时空分布规律。     

p+p碰撞中带电粒子赝快度分布的能量依赖性研究

在p+p碰撞中,只有两个带头粒子,一个处在弹碎裂区,另一个处在靶碎裂区。研究表明如同核-核碰撞一样,修正的Landau流体力学模型本身不足以对p+p碰撞中带电粒子赝快度分布的实验测量给出很好的描述,只有在考虑了带头粒子效应后,理论才能很好地与实验结果相一致。在(?)=23.6~900 GeV的整个能量范围内,理论与现有实验数据符合得很好。     

A combined model for pseudorapidity distributions in p-p collisions at center-of-mass energies from 23.6 to 7000 GeV

In p-p collisions, the charged particles produced consist of two leading particles and those frozen out from the hot and dense matter created in the collisions. The two leading particles are in the projectile and target fragmentation regions, respectively, which, in this paper, are conventionally supposed to have Gaussian rapidity distributions. The hot and dense matter is assumed to expand according to unified hydrodynamics, a hydrodynamic model which unifies the features of the Landau and Hwa-Bjorken models, and freeze out into charged particles from a space-like hypersurface with a fixed proper time of τFO. The rapidity distribution of these charged particles can be derived analytically. The combined contribution from both leading particles and unified hydrodynamics is then compared against experimental data from a now available center-of-mass energy region from 23.6 to 7000 GeV. The model predictions are consistent with experimental measurements.     

重离子碰撞中的介子——兰州重离子冷却储存环上可能实验的讨论

讨论了在兰州重离子加速装置冷却储存环上开展介子产生的实验研究的可能性和进行π和η介子产生研究的意义在 ＣＳＲ能量区域内, 核子可以激发为Δ和 Ｎ,因此, 在研究热密核物质的状态方程时, 考虑Δ和Ｎ自由度是重要的． 观察重离子碰撞中产生的介子可以提供热密核物质的状态方程, 从而可以提供核内物质分布以及 Ｎ在核物质中传播的信息． 建议建造一个测量介子的实验装置, 以开展该领域的研究.The possibilities for experimental study of meson production at Cooling Storage Ring (CSR) of Lanzhou are discussed. It is shown that the study of production of the pion and eta mesons at CSR is of significance. Nucleon can be excited to Δ and N * at CSR energy region. Therefore, it is important to consider the degree of Δ and N * in the study of the equation of states of hot and dense matter. The produced mesons in heavy ion collisions can provide information on...     

J/Ψ measurement in p+p, d+Au and Au+Au collisions by the PHENIX experiment at RHIC

J/Ψ’s are produced mostly via interactions involving gluons, and are a sensitive probe of the gluon structure function and its modification in nuclei. They are also considered as a leading signal for studying the creation of hot and dense matter in relativistic heavy ion collision. Measurement of J/Ψ production in different colliding systems is important for understanding the nuclear modification factor, and setting a baseline for the study of J/Ψ suppression in heavy ion collisions. In this talk we report the latest results on J/Ψ measurements by the PHENIX experiment at RHIC in p+p; d+Au, and Au+Au collisions at backward, forward, and mid-rapidity. Nuclear effects are studied as a function of transverse momentum, rapidity and centrality.     

Φ Meson Production in Heavy Ion Collisions at RHIC

We present Φ meson production in Cu+Cu and Au+Au collisions measured by the STAR experiment at RHIC.The hadronic decay mode Φ→K~+K~- is used in the analysis.The yields for Φ meson in Cu+Cu and Au+Au collisions at a given beam energy are scaled by the number of participant.The N_(part) normalized Φ meson yields in heavy ion collisions over those from p+p collisions are larger than 1 and increase with collision energy.These results suggest that the source of enhancement of strange hadrons is related to the formation of a dense medium in high energy heavy ion collisions and can not be only due to canonical suppression of their production in smaller systems.We also present STAR results on the Φ meson elliptic flow υ_2 from 2~(1/SNN)=200 GeV Cu+Cu at RHIC.The elliptic flow in Cu+Cu system that has the similar relative magnitude and qualitative features as that in Au+Au system.The observations imply the hot and dense matter with partonic collectivity has been formed in heavy ion collisions at RHIC.However,eccentrality normalized υ_2,υ_2/(n_qε_(part)) is lower for Cu+Cu than for Au+Au collisions at 200 GeV.So this might indicate thermalization has not been reached in 200 GeV Cu+Cu collisions.     

Jet tomography in the forward direction at RHIC

Hadron production at high p_T displays a strong suppression pattern in a wide rapidity region in heavy ion collisions at RHIC energies. This finding indicates the presence of strong final state effects for both transversally and longitudinally traveling partons, namely induced energy loss. We have developed a perturbative QCD based model to describe hadron production in pp collisions, which can be combined with the Glauber–Gribov model to describe hadron production in heavy ion collisions. Investigating AuAu and CuCu collisions at energy at mid-rapidity, we find the opacity of the strongly interacting hot matter to be proportional to the participant nucleon number. Considering forward rapidities, the suppression pattern indicates the formation of a longitudinally contracted dense deconfined zone in central heavy ion collisions. We determine the parameters for the initial geometry from the existing data. PACS 12.38.Mh, 24.85.+p, 25.75.-q     

Pulsating blobs of quark matter in relativistic nuclear collisions

The formation of hot, dense quark matter in violent high energy heavy ion collisions is discussed in a relativistic hydrodynamical model. Rapidly pulsating blobs of quark matter (treated in the bag model) are predicted to appear as a result of the expansive flow of the compressed quark matter against the contracting influence of confinement. The radial oscillations may result in pulsed matter emission.     

Lead beam experiments at the CERN SPS

The acceleration in 1986 of¹⁶O beams to 200 GeV/nucleon at the CERN SPS created a new frontier of particle and nuclear physics, namely the study of high energy density systems with hundreds of quarks and gluons created in the central collisions of nuclei with heavy targets. In order to produce the largest piece of “quark matter”, beams as heavy as²⁰⁸Pb are needed. The Lead-Injector Project that would provide them is presented. Possible experimental approaches to extract the physics from collisions with thousands of produced particles are discussed.