arXiv 1005.06452010-05nucl-thhep-phnucl-ex

相对论重离子碰撞中初始碰撞几何对喷注猝灭观测量的作用

Dissecting the role of initial collision geometry for jet quenching observables in relativistic heavy ion collisions

Jiangyong Jia, Rui Wei

备注：: 20 pages, 28 figures
发表信息：: Phys.Rev.C82:024902,2010
DOI：: 10.1103/PhysRevC.82.024902

摘要：

在$\sqrt{s_{\rm nn}}=200$ GeV的Au+Au碰撞中，观测到$p_T>5$ GeV/ $c$以上强子的大方位各向异性（$v_2$）是基于微扰QCD（pQCD）的喷注猝灭模型长期面临的挑战。使用一个简单的射流吸收模型，我们试图澄清的情况下，详细探讨如何计算的$v_2$的碰撞几何形状的选择，以及选择的路径长度依赖性和热化时间$τ_0$的能量损失公式。除了由于胶子饱和或逐事件涨落引起的畸变引起的偏心率的变化外，我们发现$v_2$对多重数的中心依赖性以及物质剖面与喷流剖面之间的相对大小也很敏感。我们发现，即使考虑了偏心率涨落和胶子饱和度，考虑了能量损失与路径长度的简单二次依赖关系的$v_2$也不足以描述高$p_T$（$\sim$ 6 GeV/ $c$）下Au+Au碰撞的实验数据.然而，如果允许能量损耗的更高功率路径长度依赖性，则它可以匹配$v_2$数据的完全中心依赖性。我们还发现，计算出的$v_2$是敏感的假设的早期动态，但一般增加与$τ_0$，相反的椭圆流的期望。这项研究证明了限制初始几何形状的重要性，可能通过结合射流淬火$v_2$与椭圆流和其他射流淬火观测，适当的解释实验数据。

英文摘要：

The observation of large azimuthal anisotropy or $v_2$ for hadrons above $p_T>5$ GeV/$c$ in Au+Au collisions at $\sqrt{s_{\rm nn}}=200$ GeV has been a longstanding challenge for jet quenching models based on perturbative QCD (pQCD). Using a simple jet absorption model, we seek to clarify the situation by exploring in detail how the calculated $v_2$ varies with choices of the collision geometry as well as choices of the path length dependence and thermalization time $τ_0$ in the energy loss formula. Besides the change of eccentricity due to distortion from gluon saturation or event-by-event fluctuation, we find that the $v_2$ is also sensitive to the centrality dependence of multiplicity and the relative size between the matter profile and the jet profile. We find that the $v_2$ calculated for the naive quadratic path length dependence of energy loss, even including eccentricity fluctuation and the gluon saturation, is not enough to describe the experimental data at high $p_T$ ($\sim$ 6 GeV/$c$) in Au+Au collisions. However, it can match the full centrality dependence of $v_2$ data if higher power path length dependence of energy loss is allowed. We also find that the calculated $v_2$ is sensitive to the assumption of the early time dynamics but generally increases with $τ_0$, opposite to what one expects for elliptic flow. This study attests to the importance of confining the initial geometry, possibly by combining jet quenching $v_2$ with elliptic flow and other jet quenching observables, for proper interpretation of the experimental data.

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