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，是一种由量子色动力学（QCD）控制的物质形式，其中单个夸克和胶子定位在核子内，预计会在距离和比飞米（fm）大很多倍的距离上散射。直到最近十年，人们才有可能在实验室中利用重离子碰撞后产生的短暂的原子核大小的等离子体液滴来创造和研究这种物质。极短的寿命（10 fm/c，其中c为光速）和小尺寸（10 fm）使该物质的研究成为理论和实验上的挑战。硬QCD射流（强相互作用的粒子束）穿过这种奇特的物质形式时的修饰提供了迄今为止研究QGP各种性质的最佳工具。这项研究的目标是继续制定一个系统和复杂的方法来对这些改进的喷气机进行理论研究。相当多的努力将被用于更深入地理解硬射流叶栅的分解，因为它们通过QGP传播时，射流中的赞助人所经历的软重新散射。然而，另一个目标将是在密集介质中数值模拟部分子级联过程，以更好地理解这种改进的阵雨的事件特征。第三个目标将是在基于微扰QCD的射流修正框架内对数据进行严格分析，以分离等离子体的输运性质，并对提取的QGP中射流的输运系数设置严格的误差条。该研究是粒子物理与核物理的交叉，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的微扰和非微扰QCD的理解。它将引入最先进的数值工具来模拟这些过程。它将引导研究生在这些工作中使用的复杂分析方法和数值模拟工具方面的训练。该项目还包括向公众传播这些分析以及其他新的前沿领域的最新结果。

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.