Fundamental Studies of the Nucleon Spin in QCD

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。作为我们可见宇宙基石的质子和中子是由更小、更基本的粒子——夸克和胶子构成的。由于支配它们相互作用的强作用力的性质，这些点状粒子或部分子被限制在核子内部。因此，半个多世纪以来，丰富、稳定且易于操纵的质子一直充当着实验的“部分子实验室”。量子色动力学（QCD）的基本机制，强相互作用的形式理论，通过对质子质量，电荷和自旋如何从部分自由度表现出来的研究来阐明。自旋是所有基本粒子固有的一种角动量，是一种纯粹的量子力学动力学，因此可以作为对量子cd本质的特别尖锐的探索。“自旋之谜”是QCD物理学中的一个突出问题，可以简单地表述为：夸克和胶子的自旋和轨道角动量是如何结合起来形成总质子自旋的1/2的？经过20年的实验，总夸克自旋的贡献限制在总和的1/3左右。这个小得惊人的数值激发了实验的动机，这些实验旨在测量风味分离的夸克自旋分布，以及自旋谜题中的胶子自旋和部分子轨道角动量。该奖项将资助实验工作，通过测量在相对论重离子对撞机的STAR探测器中重建的射流不对称性来限制胶子对自旋之谜的贡献。这些资金还将为“前进宝石追踪器”（Forward Gem Tracker）的数据采集系统的建设、测试和安装提供人力支持，该系统是STAR探测器的升级，旨在测量W生产的奇偶违反不对称性，这种不对称性对质子中分离的反上和反下夸克自旋分布很敏感。该奖项为肯塔基大学的研究生和本科生提供了学习和开发软件工具和分析技术的独特机会，以用于射流重建，同时为世界上唯一的高能极化质子对撞机的最先进探测器的建设做出贡献。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The protons and neutrons that serve as building blocks for our visible universe are constructed from smaller, more fundamental particles called quarks and gluons. These point-like particles, or partons, are confined inside nucleons due to the nature of the strong force which governs their interactions. Consequently, the abundant, stable and easily manipulated proton has served as an experimental "partonic laboratory'' for over half a century. The underlying mechanisms of Quantum Chromodynamics (QCD), the formal theory of strong interactions, are illuminated via investigations into how the proton mass, charge and spin manifest from partonic degrees of freedom.Spin, a type of angular momentum inherent to all fundamental particles, is a purely quantum mechanical dynamic and therefore serves as a particularly sharp probe into the nature of QCD. The "spin puzzle" is an outstanding question in QCD physics and can be stated simply: How does the spin and orbital angular momentum of the quarks and gluons combine to form the total proton spin of 1/2? Two decades of experiments have constrained the total quark spin contribution to be about 1/3 of the sum. This surprisingly small value motivates experiments designed to measure the flavor-separated quark spin distributions as well as the gluon spin and partonic orbital angular momentum pieces of the spin puzzle.This award will fund experimental efforts to constrain the gluon contribution to the spin puzzle via measurements of jet asymmetries as reconstructed in the STAR detector at the Relativistic Heavy Ion Collider. These funds will also support manpower for the construction, testing and installation of the data acquisition system for the Forward Gem Tracker, the STAR detector upgrade designed to measure the parity violating asymmetries of W production that are sensitive to the flavor separated anti-up and anti-down quark spin distributions in the proton. This award provides the unique opportunity for University of Kentucky graduate and undergraduate students to learn and develop the software tools and analysis techniques necessary for jet reconstruction, while simultaneously contributing to the construction of a state-of-the-art detector at the worlds only high-energy polarized proton collider.