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星星探测器重建的中快度喷流中的柯林斯不对称性来探测夸克横向分布的实验工作。 它将支持通过测量质心能量为500 GeV的质子-质子碰撞中的双喷射不对称性来进一步限制胶子对自旋之谜的贡献。 这些资金还将支持安装和调试前向宝石跟踪器的人力，这是星星探测器的升级，旨在测量违反W生产不对称性的宇称，这种不对称性对质子中味道分离的反上和反下夸克自旋分布敏感。该奖项为肯塔基州大学的研究生和本科生提供了学习和开发喷气重建所需的软件工具和分析技术的独特机会，同时还为世界上唯一的高-能量极化质子对撞机。质子和中子作为我们可见宇宙的基石，更基本的粒子称为夸克和胶子。 这些点状粒子或部分子由于支配它们相互作用的强力的性质而被限制在核子内部。 因此，丰富、稳定和易于操纵的质子已经作为实验“部分子实验室”超过半个世纪。 通过研究质子的质量、电荷和自旋如何从部分子自由度中表现出来，阐明了强相互作用的形式理论--量子色动力学（QCD）的基本机制。自旋是所有基本粒子所固有的一种角动量，是一种纯量子力学的可观测量，因此是对QCD本质的一个特别尖锐的探索。 “自旋之谜”是QCD物理学中的一个突出问题，可以简单地说： 夸克和胶子的自旋和轨道角动量是如何联合收割机结合起来形成总质子自旋为1/2的？ 二十年的实验已经将夸克自旋的贡献限制在总和的1/3左右。 然而，这个令人惊讶的小值激发了旨在测量夸克和胶子自旋分布以及自旋之谜的部分子轨道角动量的实验。

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.