arXiv 0812.11722008-12nucl-ex

$\sqrt{s_{_{NN}}}$ = 200 GeV的Cu+Cu和Au+Au碰撞中两粒子角关联对团簇性质的系统尺寸依赖性

System size dependence of cluster properties from two-particle angular correlations in Cu+Cu and Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

B. Alver

备注：: 9 pages, 8 figures, Published in Phys. Rev. C
发表信息：: Phys.Rev.C81:024904,2010
DOI：: 10.1103/PhysRevC.81.024904

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摘要：

本文研究了在宽范围的赝快度（$η$）和方位角（$ϕ$）下，每个核子对的质心能量为200 GeV的Cu+Cu和Au+Au碰撞中两粒子角关联随碰撞中心性的变化. RHIC的PHOBOS探测器对包容性带电粒子具有非常大的角覆盖范围，这使得可以研究长距离和短距离尺度上的相关性。一个复杂的二维相关结构，在$Δη$和$Δϕ$出现，这是解释的上下文中的集群模型。从两粒子赝快度关联函数中提取了有效团簇尺寸和衰变宽度。在半中心Cu+Cu和Au+Au碰撞中发现的有效团簇尺寸与质子-质子碰撞中发现的相当，但观察到随着中心度的增加，团簇尺寸显著减小。此外，从Cu+Cu和Au+Au碰撞的结果之间的比较显示了一个有趣的缩放的有效集群大小与总截面的测量分数（这是有关的影响参数的核半径，$b/2R$的比率），这表明了几何起源。对来自限制方位角区域的对的进一步分析表明，在$Δϕ\sim 180^{\circ}$处的有效团簇尺寸比在$Δϕ\sim 0^{\circ}$处的尺寸更快地朝向中心碰撞下降。有限的$η$接受集群参数的影响也得到解决，并施加校正，以目前的集群参数为全$η$覆盖，导致更大的有效集群的大小和宽度比以前在文献中指出。这些结果应该提供深入了解在重离子碰撞中产生的热和稠密介质。

英文摘要：

We present results on two-particle angular correlations in Cu+Cu and Au+Au collisions at a center of mass energy per nucleon pair of 200 GeV over a broad range of pseudorapidity ($η$) and azimuthal angle ($ϕ$) as a function of collision centrality. The PHOBOS detector at RHIC has a uniquely-large angular coverage for inclusive charged particles, which allows for the study of correlations on both long- and short-range scales. A complex two-dimensional correlation structure in $Δη$ and $Δϕ$ emerges, which is interpreted in the context of a cluster model. The effective cluster size and decay width are extracted from the two-particle pseudorapidity correlation functions. The effective cluster size found in semi-central Cu+Cu and Au+Au collisions is comparable to that found in proton-proton collisions but a non-trivial decrease of the size with increasing centrality is observed. Moreover, a comparison between results from Cu+Cu and Au+Au collisions shows an interesting scaling of the effective cluster size with the measured fraction of total cross section (which is related to the ratio of the impact parameter to the nuclear radius, $b/2R$), suggesting a geometric origin. Further analysis for pairs from restricted azimuthal regions shows that the effective cluster size at $Δϕ\sim 180^{\circ}$ drops more rapidly toward central collisions than the size at $Δϕ\sim 0^{\circ}$. The effect of limited $η$ acceptance on the cluster parameters is also addressed, and a correction is applied to present cluster parameters for full $η$ coverage, leading to much larger effective cluster sizes and widths than previously noted in the literature. These results should provide insight into the hot and dense medium created in heavy ion collisions.

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