Lepton Magnetic Moments and Fine Structure Constant

轻子磁矩和精细结构常数

• 批准号: 1903756
• 负责人: Gerald Gabrielse
• 金额: $ 81.95万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1903756&HistoricalAwards=false
• 关键词: Lepton; Magnetic; Moments; Fine; Structure

The most precise prediction made to date by a fundamental physical theory is that of a "magnetic moment," the strength of the magnet within the fundamental particle of electricity (the electron) and its antimatter counterpart (the positron). So far, measurements of the magnetism of these particles agree with prediction to a very high precision--much more precisely than those who formulated the theory ever expected. This is despite the fact that the same theory has serious problems: it predicts that no universe would survive after a big bang, and it has not been able to explain why the universe is made of matter rather than antimatter. What is wrong in our mathematical description, and the source of the fundamental imbalance between the properties of matter and antimatter, have yet to be discovered. This project will investigate such problems by measuring an electron's or positron's magnetism even more precisely than before. To do so, a single elementary particle will be suspended for months at a time. Batteries and magnets will keep the charged particle from colliding with any apparatus. Cooling the apparatus to nearly absolute zero will make a nearly perfect vacuum. To measure the magnetism, the separations of the lowest energy levels of the system will be probed by stimulating transitions between these levels using radio waves, and measuring the frequency of the waves that make these transitions occur most rapidly. This project promises to improve the measurement precision by an order of magnitude or more by stimulating two transitions simultaneously. Methods developed as part this project so far are being used to stabilize the magnets in magnetic resonance imaging (MRI) and to analyze the constituents of modern pharmaceuticals via ion cyclotron resonance (ICR) analysis. In more technical detail, a single electron or positron will be suspended in the electric and magnetic fields of a cylindrical Penning trap. Refrigeration below 0.1 kelvin will allow cryopumping to produce a nearly perfect vacuum and eliminate blackbody photons from the cylindrical cavity formed by the metal trap electrodes so the electron can radiate down to a cyclotron ground state. Electromagnetic driving forces will stimulate further cooling of the particle, and others will stimulate changes in its cyclotron and spin state. These one-quantum changes will be detected using quantum non-demolition methods that keep repeated detections from changing the quantum states of interest. Spontaneous emission of the particle's cyclotron motion will be inhibited, using a combination of the choice of the magnetic field strength and the cavity size, to give averaging times long enough for detecting a single quantum state of a single particle. The magnetic moment in natural units is essentially the measured ratio of the particle's spin and cyclotron frequencies, both of which will be measured simultaneously to greatly reduce the effect of tiny but unavoidable drifts of the magnetic field. The measured magnetic moments, the most precisely measured properties any elementary particle, will test of the most precise prediction of the standard model of particle physics at an unprecedented precision.

迄今为止，基础物理理论所做的最精确的预测是“磁矩”，即基本电粒子（电子）及其反物质对应物（正电子）中磁铁的强度。到目前为止，对这些粒子磁性的测量与预测的一致性达到了非常高的精度--比那些制定理论的人所期望的要精确得多。尽管这个理论存在严重的问题：它预言大爆炸后没有宇宙能够存活，而且它也无法解释为什么宇宙是由物质而不是反物质组成的。我们的数学描述出了什么问题，以及物质和反物质性质之间根本不平衡的根源还有待发现。该项目将通过比以前更精确地测量电子或正电子的磁性来研究这些问题。为了做到这一点，一个基本粒子将一次悬浮数月。电池和磁铁将防止带电粒子与任何仪器相撞。将设备冷却到接近绝对零度将产生接近完美的真空。为了测量磁性，系统最低能级的分离将通过使用无线电波刺激这些能级之间的跃迁来探测，并测量使这些跃迁发生得最快的波的频率。该项目有望通过同时激励两个跃迁来提高测量精度一个数量级或更多。到目前为止，作为该项目的一部分开发的方法正在用于稳定磁共振成像（MRI）中的磁体，并通过离子回旋共振（ICR）分析来分析现代药物的成分。在更多的技术细节中，单个电子或正电子将悬浮在圆柱形潘宁阱的电场和磁场中。 低于0.1开尔文的制冷将允许低温泵产生近乎完美的真空，并消除来自金属陷阱电极形成的圆柱形腔的黑体光子，因此电子可以辐射到回旋加速器基态。 电磁驱动力将刺激粒子的进一步冷却，其他驱动力将刺激其回旋和自旋状态的变化。 这些单量子变化将使用量子非破坏方法来检测，这种方法可以防止重复检测改变感兴趣的量子态。 粒子回旋运动的自发发射将被抑制，使用磁场强度和腔尺寸的选择的组合，以给出足够长的平均时间来检测单个粒子的单个量子态。 自然单位的磁矩本质上是粒子自旋和回旋频率的测量比值，这两者将同时测量，以大大减少磁场微小但不可避免的漂移的影响。 测量的磁矩是任何基本粒子最精确测量的性质，它将以前所未有的精度检验粒子物理学标准模型的最精确预测。