Jets as Probes of Ultra-Relativistic Heavy-Ion Collisions

在大爆炸后的几微秒内，整个宇宙经历了一个叫做夸克-胶子等离子体(QGP)的阶段。QGP比太阳热100多万倍，是一种受量子色动力学(QCD)支配的物质形式，位于核子中的单个夸克和胶子预计会在比飞秒计(FM)大许多倍的距离内散射出去。只有在过去的十年里，才有可能在实验室里使用重离子碰撞后产生的短暂的核大小的等离子体液滴来创造和研究这种形式的物质。非常短的寿命(10fm/c，其中c是光速)和小尺寸(10fm)使得对这一物质的研究成为理论和实验上的挑战。硬QCD喷流(强相互作用粒子束)穿过这种奇异形式的物质时的修正是迄今为止研究QGP各种性质的最佳工具。这笔赠款支持的研究的目标是继续制定一种系统和复杂的方法来对这些改装的喷气式飞机进行理论研究。相当大的努力将被用于更深入地理解硬喷流瀑布的因式分解，从喷流中的赞助人经历的软再散射中，当它们通过QGP传播时。另一个目标将是对稠密介质中的部分子级联过程进行数值模拟，以更好地了解这种修改后的阵雨的逐个事件特征。第三个目标是在基于微扰QCD的喷注修正框架内对数据进行严格的分析，以分离等离子体的输运性质，并在QGP中提取的喷注的输运系数上设置严格的误差条。这项研究是粒子物理和核物理的交叉点，将极大地增强我们对动态膨胀夸克胶子等离子体复杂环境中微扰和非微扰QCD的理解。它将引入最先进的数值工具来模拟这样的过程。它将导致对研究生进行复杂的分析方法以及在这种努力中使用的数值模拟工具的培训。该项目还包括一项外联工作，向公众传达此类分析以及其他新的前沿领域的最新成果。

For several microseconds after the big bang the entire universe passed through a phase called the Quark-Gluon Plasma (QGP). More than a million times hotter than the sun, the QGP is a form of matter governed by quantum chromodynamics (QCD) where the individual quarks and gluons localized within nucleons are expected to scatter out over distances and times many times larger than a femtometer (fm). Only in the last ten years has it become possible to create and study this form of matter in the laboratory using the fleetingly short-lived nuclear sized droplets of plasma created in the aftermath of a heavy-ion collision. The very short lifetime (10 fm/c, where c is the speed of light) and small size (10 fm) have made the study of this matter a theoretical and experimental challenge. The modification of hard QCD jets (bundles of strongly interacting particles) as they pass through this exotic form of matter presents the best tool to date to study the various properties of the QGP. The goal of the research supported by this grant is to continue to formulate both a systematic and sophisticated approach to the theoretical study of these modified jets. Considerable effort will be directed towards a deeper understanding of the factorization of the hard jet cascade from the soft rescattering experienced by the patrons in the jet, as they propagate through the QGP. Yet another goal will be to numerically simulate the partonic cascade process within the dense medium to better understand the event-by-event characteristics of such modified showers. A third goal will be a rigorous analysis of the data within the framework of perturbative QCD based jet modification to isolate the transport properties of the plasma and place stringent error bars on the extracted transport coefficients of jets in a QGP.This research, at the intersection of particle and nuclear physics, will greatly enhance our understanding of perturbative and non-perturbative QCD in the complicated environments of a dynamically expanding quark gluon plasma. It will introduce state of the art numerical tools to simulate such processes. It will lead to the training of graduate students in both the sophisticated analytical approaches used as well as the numerical simulation tools used in such efforts. The project also includes an outreach effort to convey the latest results from such analyses as well as from other new cutting edge fields to the general public.