Unified Hydrodynamics and Pseudorapidity Distributions of Charged Particles Produced in Heavy Ion Collisions at Low Energies at RHIC

In the context of unified hydrodynamics, we discuss the pseudorapidity distributions of the charged particles produced in Au-Au and Cu-Cu collisions at the low RHIC energies of √SNN = 19.6 and 22.4 GeV, respectively. It is found that the unified hydrodynamics alone can give a good description to the experimental measurements. This is different from the collisions at the maximum RHIC energy of √SNN = 200 GeV or at LHC energy of √SNN= 2.76 TeV, in which the leading particles must be taken into account so that we can properly explain the experimental observations.

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 TFo. 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.

A description of pseudorapidity distributions in p-p collisions at center-of-mass energy from 23.6 to 900 GeV

In the context of the combined model of evolution-dominated hydrodynamics ＋ leading particles, we discuss the pseudorapidity distributions of charged particles produced in p-p collisions. A comparison is made between the theoretical predictions and experimental measurements. The combined model works well in p-p collisions in the whole available energy region from √s=23.6 to 900 GeV.

Pseudorapidity distributions of the produced charged particles in nucleus-nucleus collisions at low energies at the BNL relativistic heavy ion collider

The revised Landau hydrodynamic model is used to discuss the pseudorapidity distributions of the produced charged particles in Au＋Au and Cu＋Cu collisions at energies of s √SNN=19.6 and 22.4 GeV respectively at the BNL Relativistic Heavy Ion Collider. It is found that the revised Landau hydrodynamic model alone can give a good description of the experimental measurements. This is different from the result with the same collisions but at the maximum energy of√SNN=200 GeV, where in addition to the revised Landau hydrodynamic model, the effects of leading particles have to be taken into account in order to explain the experimental observations. This can be attributed to the different degrees of transparency of participants at the different incident energies.

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√sNN=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。

Hwa-Bjorken与Landau相对论流体力学的统一描述与高能重离子碰撞中的赝快度分布

近年来,高能物理界取得的最重要的成就之一是发现高能重离子碰撞产生的高温高密度物质极近理想流体。描述这种流体膨胀过程的最佳工具是相对论流体力学。在Hwa-Bjorken与Landau相对论流体力学统一描述理论的基础上,考虑到带头粒子的贡献,讨论了带电粒子的赝快度分布。由流体冻析产生的带电粒子的快度分布可由统一流体力学理论解析得到,带头粒子的快度分布假设具有高斯形式。与LHC-RHICPHOBOS合作组在能量分别为s _NN^(1/2)=62.4与130 GeV的Au-Au碰撞中的实验测量相比较得知,理论与实验结果符合得很好。

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。