Fundamental Studies of the Proton Spin in QCD

该奖项将资助通过测量相对论重离子对撞机恒星探测器中重建的中快度喷流中的柯林斯不对称性来探测夸克横度分布的实验努力。它将通过测量质心能量为500GeV的质子-质子碰撞中的双喷流不对称性，支持进一步限制胶子对自旋谜题的贡献的努力。这些资金还将支持安装和调试Forward Gem Tracker的人力，这是一种恒星探测器升级，旨在测量W生产中违反宇称的不对称性，这些不对称性对质子中分离的反向上和反向下夸克自旋分布非常敏感。这一奖项为肯塔基大学的研究生和本科生提供了一个独特的机会，让他们学习和开发喷流重建所需的软件工具和分析技术，同时为世界上唯一的高能极化质子对撞机安装和调试最先进的探测器做出贡献。作为我们可见宇宙的基石的质子和中子是由更小的、更基本的称为夸克和胶子的粒子构成的。由于控制核子相互作用的强力的性质，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，这种丰富、稳定和易于操作的质子一直是一个实验的“部分实验室”。量子色动力学(QCD)是强相互作用的形式理论，通过研究质子质量、电荷和自旋如何在部分子自由度上表现出来，阐明了量子色动力学(QCD)的基本机制。自旋是所有基本粒子固有的一种角动量，是纯粹的量子力学可观测的，因此是对QCD本质的特别尖锐的探索。自旋之谜是QCD物理学中的一个悬而未决的问题，可以简单地说：夸克和胶子的自旋和轨道角动量是如何结合在一起形成1/2的总质子自旋的？二十年的实验已经将总夸克自旋贡献限制在总和的1/3左右。然而，这个令人惊讶的小数值激发了旨在测量夸克和胶子自旋分布以及自旋拼图中的部分子轨道角动量碎片的实验。

This award will fund experimental efforts to probe the quark transversity distributions via measurements of Collins asymmetries in mid-rapdity jets reconstructed in the STAR detector at the Relativistic Heavy Ion Collider. It will support efforts to further constrain the gluon contribution to the spin puzzle via measurements of dijet asymmetries in proton-proton collisions at center-of-mass energies of 500 GeV. These funds will also support manpower for the installation and commissioning of 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 the 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 installation and commissioning of a state-of-the-art detector at the world's only high-energy polarized proton collider.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 observable 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 ~1/3 of the sum. However, the surprisingly small value motivates experiments designed to measure the quark and gluon spin distributions and partonic orbital angular momentum pieces of the spin puzzle.