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arXiv 0901.2818hep-ph
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中等修正的QCD阵雨演变情景的比较研究

A comparison study of medium-modified QCD shower evolution scenarios

Thorsten Renk

备注：
15 pages, 10 figures, minor changes
发表信息：
Phys.Rev.C79:054906,2009
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摘要：

强子碰撞中硬过程的计算是微扰量子色动力学（pQCD）的一个重要成就。在这样的过程中，pQCD不仅预测了硬反应本身，还预测了随后部分子分支和辐射的演化，导致部分子簇射，最终导致可观察到的强子喷流。如果硬过程发生在重离子碰撞中，那么这种演化的很大一部分发生在与硬反应一起产生的软介质中。因此，观测重离子碰撞中的喷流可以研究介质修正的QCD簇射演化。在真空中，蒙特卡罗（MC）模拟是描述这种簇射的成熟工具。对于重离子碰撞中的喷流研究，目前正在开发介质簇射的MC模型。然而，质子-介质相互作用依赖于重离子碰撞中产生的介质的微观自由度的性质，这正是人们想要研究的对象。本文提出了一种研究在比较三种不同的可能实现的介质-介质相互作用，其中两个基于介质诱导的pQCD辐射，其中一个介质诱导的阻力，并显示了这三种情况之间的可观测差异变得明显。我们发现，虽然单个强子观测值，如R_AA是无法区分的情况下，喷流观测值，如强子在喷流的纵向动量谱显示出这样做的潜力。

英文摘要：

The computation of hard processes in hadronic collisions is a major success of perturbative Quantum Chromodynamics (pQCD). In such processes, pQCD not only predicts the hard reaction itself, but also the subsequent evolution in terms of parton branching and radiation, leading to a parton shower and ultimately to an observable jet of hadrons. If the hard process occurs in a heavy-ion collision, a large part of this evolution takes place in the soft medium created along with the hard reaction. An observation of jets in heavy-ion collision thus allows a study of medium-modified QCD shower evolution. In vacuum, Monte-Carlo (MC) simulations are well established tools to describe such showers. For jet studies in heavy-ion collisions, MC models for in-medium showers are currently being developed. However, the shower-medium interaction depends on the nature of the microscopic degrees of freedom of the medium created in a heavy-ion collision which is the very object one would like to investigate. This paper presents a study in comparison between three different possible implementations for the shower-medium interaction, two of them based on medium-induced pQCD radiation, one of them a medium-induced drag force, and shows for which observables differences between the three scenarios become visible. We find that while single hadron observables such as R_AA are incapable of differentiating between the scenarios, jet observables such as the longiudinal momentum spectrum of hadrons in the jet show the potential to do so.

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