RUI: A Search for Long-Range Spin-Spin Interactions and Optical Forces in TlF

对基本粒子自转的精确测量可以为我们提供对自然基本规律的新见解。基本粒子具有一种名为自旋的内在属性，这使它们的行为就像它们像机械顶部一样不断旋转一样。就像原子顶在重力作用下运动一样，基本粒子的自旋也在磁场中运动。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本物理，称为磁共振成像(MRI)。最近发展起来的精密光学技术使得研究与粒子自旋的相互作用具有前所未有的保真度。这个项目将使用这些精密技术作为工具来研究自然界的基本力和对称性。在最基本的层面上，物理学家目前对自然的理解是由粒子物理的“标准模型”概括的。这个模型需要四个基本力(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，研究人员将寻找一种新的粒子自旋之间的长程力，这是标准模型无法描述的。为了优化他们的搜索，他们将测量他们的实验室自旋与地球内所有排列的电子自旋的相互作用。在他们的另一项实验中，研究人员希望最终能看到自然界的基本规律是否在时间上是不对称的。这种“时间对称性”的破缺可以通过研究原子核自旋在电场中的进动来研究。在这里，通过使用一束非常冷的分子来提高实验的灵敏度。额外的时间不对称性(超出已经观察到的时间)被认为是解释我们宇宙存在的必要因素。如果没有时间反转破坏，我们的宇宙将会产生等量的物质和反物质。它们的相互湮灭不会允许星系、恒星、行星和生命的形成。2013年，研究人员绘制了第一张地球内部电子自旋密度图。这些“地电子”构成了已知的最大极化自旋源。在实验室中精确测量地球表面的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和实验室自旋之间的远程自旋-自旋相互作用(LRSSI)。在第一个拟议的实验中，将建造一个精致的自旋进动装置，它既经过很好的校准，又相对不受交流光效应的影响。这应该允许这些LRSSI测量的灵敏度至少提高一个数量级。如果能看到某种影响，那就意味着一种新的自然力量的存在。在目前的模型中，这种力可能与超轻矢量介子、“暗光子”、“非粒子”或扭曲引力有关。在第二个拟议的实验中，研究人员将继续他们对关键参数的研究，这些参数最终将决定目前由Centrex合作在耶鲁大学建造的TLF电偶极矩(EDM)实验的灵敏度。具体地说，研究人员希望继续改进他们对TLF中光学循环的测量，并证明这种循环可以用来对TLF施加光学力。这些光学力将被用来横向冷却TLF的低温分子束。这种横向冷却将使TLF电火花加工实验的灵敏度提高约一个数量级。有了这种额外的敏感性，就有可能发现永久性的核电火花加工。如果这个EDM被发现，它将意味着违反了时间对称性，并可能有助于解释我们以物质为主导的宇宙的存在。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Precision measurements of elementary particles' spins can provide new insight into the fundamental laws of nature. Elementary particles have an intrinsic property called spin which makes them act as if they are constantly rotating like mechanical 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. This project will use these precision techniques as tools to investigate the fundamental forces and symmetries of nature. At the most basic level, physicists' present understanding of nature is summarized by 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 can't 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 beam of very cold 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. 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 will be constructed 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) electric-dipole moment (edm) experiment that is presently being constructed at Yale 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 transversely cool a cryogenic molecular beam of TlF. This transverse cooling should increase the sensitivity of the TlF edm experiment by about an order of magnitude. With this additional sensitivity it is possible that a permanent nuclear edm will be discovered. If this edm is found, it 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.