【作者】 司瑞芳；

【导师】 刘福虎；

【作者基本信息】 山西大学 ， 粒子物理与原子核物理， 2012， 硕士

【摘要】 本文应用多源热模型模拟计算了质心系能量为22.4A、62.4A、200A GeV的Cu-Cu碰撞中,在0-6%、6-15%中心度范围内的事例中,末态带电粒子的赝快度分布,以及入射能量为25MeV/N的Kr-Sn碰撞中,末态核碎片的方位角分布,及椭圆流对横动量的依赖关系。结果表明,多源热模型仅利用几个简单的参数,就较好地重现了中高能重离子碰撞中的纵向赝快度分布和横向方位角分布、及椭圆流对横动量依赖的实验数据,或其他模型的计算结果。本文得到的主要结果可概括为以下两方面：(1)从RHIC能区Cu-Cu碰撞中末态粒子的赝快度分布可以看出,随着碰撞能量的提高,赝快度分布宽度变宽,密度增高,且.在两中心度比较下其变化趋势一致,但中心度为6-15%的事例中的粒子产额比中心度为0-6%的事例中的粒子产额稍低。另外从模拟曲线看,最后的赝快度分布是由对称分布的两组四个近似高斯曲线叠加而成的。很明显单个的高斯分布不能描写赝快度的这种双峰分布,这也就否定了利用单一静止热源模型继续分析碰撞系统的可能性。无论采用那种模型,都认为赝快度分布宽度变宽是系统纵向扩散产生纵向流的表现。再联系到粒子产额,说明次级碰撞对赝快度分布宽度有绝对影响。而赝快度分布宽度随能量变宽,说明随着能量提高,核阻止度下降,系统越来越透明。(2)从MeV能区Kr-Sn碰撞中产生的核碎片的方位角分布可以看出,由于空间各向异性,核碎片的方位角分布不再各向同性,而是出现与方位角关联的振荡,表现为一条上下起伏的曲线。且质量越大的核碎片,方位角分布的振荡越大,说明质量越大的核碎片各向异性分布越明显。从MeV能区Kr-Sn碰撞中产生的核碎片的椭圆流对横动量的依赖关系可以看出,在横动量空间,核碎片的分布不再为各向同性的圆,而是椭圆,且随着核碎片横动量的增加,各向异性程度增强,椭圆流变大。核碎片质量越大椭圆流也越大,说明椭圆流与系统碰撞形成的压力强度相关,质量对椭圆流影响明显。更多还原

【Abstract】 The pseudorapidity distributions of final-state charged particles produced in Cu-Cu collisions with centralities0-6%and6-15%at22.4A,62.4A, and200A GeV are calculated by using the multi-source thermal model. Meanwhile, the azimuthal distributions and the dependences of elliptic flows on transverse momentum for nuclear fragments produced in Kr-Sn collisions at25Me V/N are calculated by the model. It is shown that the model with a few simple parameters is successful in the descriptions of longitudinal pseudorapidity distributions, transverse azimuthal distributions, and the dependences of elliptic flows on transverse momentum. Our results calculated by the model are in agreement with the experimental data or other modeling results. The main results obtained in the present work can be summarized as two parts given in the following.(1) From the pseudorapidity distributions of final-state particles in Cu-Cu collisions at the RHIC energies, one can see that the distribution width and density increase with increasing the impact energy. These situations are the same for the two centralities. However, the density for centrality6-16%is slightly lower than that for centrality0-6%. The final-state pseudorapidity distribution is described by a sum of four Gaussian-like functions. A single Gaussian function does not describe the two-peak structure of pseudorapidity distribution. As representations of longitudinal flow effect and secondary collisions, the width of pseudorapidity distribution becomes wider.(2) From the azimuthal distributions of nuclear fragments produced in25MeV/N Kr-Sn collisions, one can see that the emission of fragments is anisotropic. There are fluctuations in the azimuthal range. The heavy fragments have large fluctuation and anisotropy. From the dependences of elliptic flows on transverse momentum, one can see that the fragments distribute in a ellipse in the space of transverse momentum. A large transverse momentum corresponds to a large elliptic flow. On the other hand, the heavy fragments have large elliptic flow.更多还原