ACME III: Advanced Cold Molecule Electron Electric Dipole Moment Search

ACME III：高级冷分子电子电偶极矩搜索

• 批准号: 1912513
• 负责人: David DeMille
• 金额: $ 376.71万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1912513&HistoricalAwards=false
• 关键词: ACME; III; Advanced; Cold; Molecule

The goal of this project is to search for a new fundamental property of the electron, one of the main constituents of matter and a charged component of all atoms. This new property, called an electric dipole moment, can be described as a slight bulge on an otherwise perfect sphere of charge. This seemingly abstruse feature may hold the key to one of the most fundamental mysteries of nature: why is everything in the universe made of matter rather than of antimatter? In accelerator laboratories, whenever energy is converted into particles (according to E=mc2), equal numbers of matter particles and antimatter particles are created. For example, the electron has a counterpart antimatter particle, the anti-electron, which has identical mass but opposite electric charge. Energy can be converted into an electron/anti-electron pair, and conversely an electron and anti-electron can annihilate each other and turn into energy. Just after the Big Bang, energy was converted into particles and anti-particles. Astronomical observations show that since then, essentially all the antimatter annihilated with matter--but a tiny bit of matter was left over. That small excess makes up all of the objects seen in the Universe today. The current framework that describes all known fundamental forces between elementary particles, known as the "Standard Model", cannot explain how this excess of matter survived. However, many mathematical theories have been devised that can explain this "matter-antimatter asymmetry", by positing new forces and particles not yet discovered in any experiment. These same new forces and particles also often lead, according to the same theories, to an electric dipole moment that is large enough to observe in the experiment supported here. Hence, this project is essentially seeking an answer to the question: how is it that matter was slightly preferred over anti-matter at some time in the past, resulting in the physical Universe seen today? In a general sense, this project also advances the range of techniques for precision measurement science, which in the past has led to unexpected breakthroughs in technology such as GPS (the Global Positioning System), new types of sensors, etc. The electric dipole moment (EDM), if it exists, must lie along the spin axis of the electron. In the presence of a nonzero EDM, an electric field will induce a torque on the electron, resulting in precession of the spin about the field. This spin precession angle is the experimental signal. The huge internal electric field of a polar molecule, ThO, is used to amplify this observable effect. The internal structure of ThO also suppresses possible systematic errors. A cryogenic molecular beam source that delivers an unprecedented high flux of molecules is used. Lasers and optical techniques put the ThO molecules in usable coherent superpositions and then probe the quantum interference that signals the electron's spin precession. Over the previous grant period, a version of these methods was used to make the most sensitive measurement of the electron's EDM. This result was consistent with a zero value for the EDM. However, many theories of what lies beyond the Standard Model of particle physics predict that, with improved sensitivity, detection of the EDM is likely. In this project, methods to greatly improve the sensitivity of the experiment will be introduced. These include focusing of the molecular beam and a use of longer interaction region to increase the time that a torque acts on the EDM. Improvements to reduce systematic errors observed in the previous experiment, such as the use of more carefully controlled magnetic fields and low-birefringence optical elements, will also be incorporated.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.

该项目的目标是寻找电子的新基本属性，电子是物质的主要成分之一，也是所有原子的带电成分。这种新特性被称为电偶极矩，可以描述为原本完美的电荷球上的轻微凸起。这个看似深奥的特征可能掌握着自然界最基本奥秘之一的关键：为什么宇宙中的一切都是由物质而不是反物质组成的？在加速器实验室中，每当能量转化为粒子（根据 E=mc2）时，就会产生相同数量的物质粒子和反物质粒子。例如，电子有一个对应的反物质粒子，即反电子，它具有相同的质量但具有相反的电荷。能量可以转化为电子/反电子对，反之电子和反电子可以相互湮灭而转化为能量。大爆炸后不久，能量就转化为粒子和反粒子。天文观测表明，从那时起，基本上所有的反物质都被物质湮灭了，但留下了极少量的物质。这个小小的多余部分构成了当今宇宙中看到的所有物体。当前描述基本粒子之间所有已知基本力的框架（称为“标准模型”）无法解释这种过量的物质是如何幸存下来的。然而，许多数学理论已经被设计出来，可以通过假设尚未在任何实验中发现的新力和粒子来解释这种“物质-反物质不对称性”。根据相同的理论，这些相同的新力和粒子也常常导致电偶极矩足够大，可以在此处支持的实验中观察到。因此，这个项目本质上是在寻找这个问题的答案：在过去的某个时间，物质为何比反物质略受青睐，从而导致了今天所看到的物理宇宙？从一般意义上讲，该项目还推进了精密测量科学的技术范围，这些技术在过去曾导致 GPS（全球定位系统）、新型传感器等技术取得意想不到的突破。电偶极矩（EDM）如果存在，则必定位于电子的自旋轴上。在存在非零 EDM 的情况下，电场将在电子上感应出扭矩，从而导致绕场的自旋进动。该自旋进动角就是实验信号。极性分子 ThO 的巨大内部电场被用来放大这种可观察到的效应。 ThO 的内部结构也抑制了可能的系统错误。使用可提供前所未有的高分子通量的低温分子束源。激光和光学技术将 ThO 分子置于可用的相干叠加态，然后探测发出电子自旋进动信号的量子干涉。在之前的资助期内，这些方法的一个版本被用来对电子 EDM 进行最灵敏的测量。该结果与 EDM 的零值一致。然而，许多超出粒子物理标准模型的理论预测，随着灵敏度的提高，有可能检测到 EDM。在这个项目中，将介绍大大提高实验灵敏度的方法。其中包括分子束的聚焦和使用更长的相互作用区域来增加扭矩作用在 EDM 上的时间。 还将纳入减少先前实验中观察到的系统误差的改进，例如使用更仔细控制的磁场和低双折射光学元件。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。