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arXiv 0906.2260nucl-ex
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RHIC前向快度光子产生的质心能量和系统尺寸依赖性

Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

STAR Collaboration, B. I. Abelev

摘要:

我们给出了在\sqrt{s_NN} = 62.4和200 GeV的Au+Au和Cu+Cu碰撞中产生的光子的多重数和赝快度分布。在RHIC的STAR实验中,使用光子多重性探测器在-3.7 < η< -2.3区域测量光子。每平均参与核子对产生的光子数随束能量的增加而增加,与碰撞中心性无关。对于具有相似平均参与核子数的碰撞,在给定的束能量下,观察到Au+Au和Cu+Cu碰撞的光子多重性是相似的。在测量的赝快度范围内,当\sqrt{s_NN} = 62.4 GeV和200 GeV时,带电粒子数与光子数之比分别为1.4 +/- 0.1和1.2 +/- 0.1。这个比率的能量依赖性可以反映重子对带电粒子的不同贡献,而介子是给定运动学区域中光子产生的主要贡献者。用平均参与核子对数归一化的光子赝快度分布,在两种束流能量下,都遵循与中心性和碰撞离子种类无关的纵向标度。

英文摘要:

We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < η< -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for \sqrt{s_NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of η- ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.

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