PM: RUI: Searching for Optical Cycling in TlF and Long-Range Spin-Spin Interactions

PM：RUI：寻找 TlF 和长程自旋-自旋相互作用中的光学循环

• 批准号: 2110523
• 负责人: Larry Hunter
• 金额: $ 48.62万
• 依托单位: Amherst College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2110523&HistoricalAwards=false
• 关键词: PM; RUI; Searching; Optical; Cycling

Precision measurements of the spin interactions of elementary particles can provide new insights into the fundamental laws of nature. Elementary particles have an intrinsic property called spin – they act as if they are constantly spinning around like tops. Just as tops precess in the presence of gravity, the spins of fundamental particles precess in a magnetic field. This precession is the basis of nuclear magnetic resonance which is the underlying physics used in the medical diagnostic known as magnetic resonance imaging (MRI). Recently developed precision optical techniques have allowed the study of interactions with particle spins with unprecedented fidelity. The researchers will use these techniques as tools to investigate the fundamental forces and symmetries of nature. At the most basic level, our present understanding of nature is summarized in the “Standard Model” of particle physics. This model requires four fundamental forces (gravitational, electromagnetic, strong and weak) to describe all of reality as it is presently known. In one experiment, the investigators will look for a new long-range force between particle spins that cannot be described by the Standard Model. To optimize their search, they will measure the interaction of their laboratory spins with all of the aligned electron spins within the Earth. In their other experiment, the researchers hope eventually to see if the fundamental laws of nature might be asymmetric in time. This breaking of “time symmetry” can be studied by looking for the precession of a nuclear spin in an electric field. Here the experimental sensitivity is increased by using a very cold beam of molecules. Additional time asymmetry (beyond that which has already been observed) is believed to be necessary to explain the existence of our universe. Without time-reversal violation, our universe would have produced equal amounts of matter and anti-matter. Their mutual annihilation would not have allowed for the formation of galaxies, stars, planets and life. The pursuit of these experiments will provide an enticing introduction to STEM for many undergraduate students and provide continue experiences for the next generation of STEM researchers.In 2013 the researchers created the first map of the electron-spin density within the Earth. These “geo-electrons” constitute the largest polarized spin source known. Precision measurement of spin-precession frequencies in laboratories at the surface of the Earth as a function of the magnetic-field direction, allows one to look for long-range spin-spin interactions (LRSSI) between the geo-electrons and the laboratory spins. In the first proposed experiment, a refined spin-precession apparatus is under construction which is both well-calibrated and relatively immune to AC light effects. This should allow at least an order of magnitude improvement in the sensitivity of these LRSSI measurements. If an effect is seen it would suggest the existence of a new force of nature. In current models this force might be associated with an ultra-light vector meson, a “dark” photon, the “unparticle”, or torsion gravity. In the second proposed experiment, the researchers will continue their investigation of critical parameters that will ultimately determine the sensitivity of the thallium fluoride (TlF) nuclear electric-dipole moment (nEDM) experiment that is presently being constructed at Argon National Lab by the CeNTREX collaboration. Specifically, the researchers hope to continue to improve their measurements of optical cycling in TlF and to demonstrate that this cycling can be used to exert optical forces on TlF. These optical forces will be used to transverse cool a cryogenic molecular beam of TlF. If successful, transverse cooling could increase the sensitivity of the TlF nEDM experiment by about an order of magnitude. With this additional sensitivity it is possible that a permanent nEDM will be found. Such a discovery would imply a violation of time symmetry and could help explain the existence of our matter-dominated universe.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

对基本粒子自旋相互作用的精确测量可以提供对自然基本定律的新见解。 基本粒子具有一种称为自旋的内在属性——它们的行为就好像它们像陀螺一样不断旋转。 正如陀螺在重力作用下进动一样，基本粒子的自旋在磁场中进动。 这种进动是核磁共振的基础，核磁共振是医学诊断中使用的基础物理学，即磁共振成像 (MRI)。 最近开发的精密光学技术使得以前所未有的保真度研究粒子自旋的相互作用。 研究人员将使用这些技术作为研究自然的基本力和对称性的工具。 在最基本的层面上，我们目前对自然的理解被总结在粒子物理学的“标准模型”中。 该模型需要四种基本力（引力、电磁力、强力和弱力）来描述目前已知的所有现实。 在一项实验中，研究人员将寻找标准模型无法描述的粒子自旋之间的新的远程力。 为了优化他们的搜索，他们将测量实验室自旋与地球内所有对齐电子自旋的相互作用。 在他们的另一个实验中，研究人员希望最终看看自然的基本定律是否可能在时间上不对称。 这种“时间对称性”的破坏可以通过寻找电场中核自旋的进动来研究。 这里通过使用非常冷的分子束来提高实验灵敏度。 人们认为额外的时间不对称性（超出已经观察到的时间不对称性）对于解释我们宇宙的存在是必要的。 如果没有时间反转破坏，我们的宇宙就会产生等量的物质和反物质。 它们的相互湮灭不会导致星系、恒星、行星和生命的形成。 对这些实验的追求将为许多本科生提供对 STEM 的引人入胜的介绍，并为下一代 STEM 研究人员提供持续的经验。2013 年，研究人员创建了第一张地球内电子自旋密度图。 这些“地电子”构成了已知的最大的极化自旋源。 在地球表面的实验室中精确测量自旋进动频率作为磁场方向的函数，使人们能够寻找地球电子与实验室自旋之间的长程自旋-自旋相互作用（LRSSI）。 在第一个提出的实验中，正在建造一个精制的自旋进动装置，该装置经过良好校准，并且相对不受交流光效应的影响。 这应该可以使这些 LRSSI 测量的灵敏度至少提高一个数量级。 如果看到效果，则表明存在新的自然力。 在当前模型中，这种力可能与超轻矢量介子、“暗”光子、“非粒子”或扭转引力有关。 在第二个拟议的实验中，研究人员将继续研究关键参数，这些参数将最终确定氟化铊 (TlF) 核电偶极矩 (nEDM) 实验的灵敏度，该实验目前由 CeNTREX 合作在氩国家实验室构建。具体来说，研究人员希望继续改进对 TlF 中光学循环的测量，并证明这种循环可用于对 TlF 施加光学力。 这些光学力将用于横向冷却 TlF 低温分子束。 如果成功，横向冷却可以将 TlF nEDM 实验的灵敏度提高大约一个数量级。 有了这种额外的灵敏度，就有可能找到永久的 nEDM。 这样的发现意味着违反时间对称性，并有助于解释我们以物质为主的宇宙的存在。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。