MRI: Development of an Instrument for Ultra-High Resolution 1S-2S Spectrosopy of Exotic Hydrogenic Atoms

我们关于原子结构和相互作用的最精确的信息最终是基于对各种原子和分子发射和吸收的光的精确测量。该光的颜色光谱（或“共振频率”）为计算和测量提供了基本输入，这些计算和测量用于化学鉴定、反应速率估计以及在从医学到国防的广泛应用中预测新结构的稳定性。和制造业的质量控制。最近，对不同类型的氢原子（由一个中心重质子和一个行星状电子或μ子组成）的测量在质子半径上存在分歧。这种差异表明了三种可能性之一：（1）带电粒子如何相互作用的理论，称为量子电动力学或QED，是不正确的;（2）我们对质子结构的认识是不正确的;或者（3）有某种新的相互作用或自然力尚未被发现。为了确定这个谜团是否是由于量子电动力学的问题，来自加州大学滨江分校（UCR）的两名科学家提议开发一种新的仪器，这种仪器将能够测量电子偶素的共振频率，其精度最终比目前的技术水平高出1000倍。因为电子偶素是最简单的原子，由一个电子和一个反电子结合在一起，QED理论应该能很好地描述它。使用拟议中的仪器进行的新测量将决定QED理论是否是问题所在，并对我们对质子结构的理解的差异设定更高的限制。这台新仪器将在精密光谱学领域的前沿改进不稳定原子的光谱学。纯轻子原子电子偶素（Ps）非常适合测试束缚态量子电动力学（QED），并提供了理解和背景，使我们可以从较重轻子和强子的精确原子测量中提取非QED物理。很少有人敢尝试在万亿分之几的水平上测量正电子素，这将使人们能够深入了解物理学，如质子电荷半径和μ素中更高水平的反冲效应修正，并且可能显示轻轻子和重轻子之间的差异。精确测量正电子偶素的理想能级间距是1 S-2S间隔，约为1233607216 MHz。这个间隔的前10位的知识已经存在了20年，不确定度为±3 MHz。拟议的仪器将实施几项新技术，通过高精度的单个原子轨迹分析，允许以kHz的精度测量线中心，从而显着提高Ps原子光谱学的准确性，并可能提高其他高分辨率光谱学实验的准确性。通过记录与热稳定超低膨胀玻璃参考腔的线中心的瞬时偏差，将以亚kHz的相对和绝对精度完成原子通过激光场的传输期间的激光频率计量，所述热稳定超低膨胀玻璃参考腔使用GPS纪律RF参考频率梳进行校准。通过提供超稳定的环境、机械和振动隔离，该仪器的总体规格将足以产生窄线宽（~2 MHz）、系统误差的减少以使精度提高高达1000倍、以及高10倍的计数率以使在可管理的测量持续时间（数月与数年）内进行精确测量。

Our most precise information about the structure and interactions of atoms is ultimately based on precise measurements of the light that is emitted and absorbed by various atoms and molecules. The spectrum of colors (or "resonant frequencies") of this light provides the basic input to calculations and measurements that are used for chemical identification, for reaction rate estimates, and for predictions of stability of new structures in a broad range of applications from medicine to defense and quality control in manufacturing. Recently, measurements on different types of hydrogen atoms (consisting of a central heavy proton and a planet-like electron or muon) are in disagreement about the radius of the proton. The discrepancy suggests one of 3 possibilities: (1) the theory of how charged particles interact, known as quantum electrodynamics or QED, is incorrect; (2) our knowledge of the structure of the proton is incorrect; or (3) there is some new kind of interaction or force of nature yet to be discovered. To decide whether the mystery is due to a problem with QED or not, two scientists from the University of California Riverside (UCR) propose to develop a novel instrument that will enable a measurement of the resonant frequency of positronium at ultimately 1000X more accuracy than the current state of the art. Because positronium is the simplest possible atom, consisting of an electron bound to an anti-electron, it should be described perfectly by QED theory. New measurements with the proposed instrument will decide whether QED theory is the problem and set significantly higher limits on the discrepancy in our understanding of the structure of the proton. The new instrument will lead to an improvement in the spectroscopy of unstable atoms at the frontier of the field of precision spectroscopy. The purely leptonic atom positronium (Ps) is uniquely well-suited for testing bound-state quantum electrodynamics (QED) and provides the understanding and background by which we may extract non-QED physics out of precision atomic measurements on heavier leptons and hadrons. Few have dared to try measurements on positronium at the few parts per trillion level that would allow insight into physics such as the proton charge radius and higher level recoil effect corrections in muonium, and that might show differences between light and heavy leptons. The ideal level spacing for a precision measurement on positronium is the 1S-2S interval at approximately 1 233 607 216 MHz. Knowledge of the first 10 digits of this interval has stood for 20 years with an uncertainty of ±3 MHz. The proposed instrument will implement several new techniques that would dramatically improve the accuracy of Ps atom spectroscopy and potentially other high resolution spectroscopy experiments by high precision individual atom trajectory analysis allowing line-centers to be measured to kHz precision. The laser frequency metrology during the transit of the atoms through the laser field will be accomplished with sub-kHz relative and absolute accuracies by recording the instantaneous deviations from the line-center of a thermally-stabilized ultra-low expansion glass reference cavity that is calibrated using a GPS-disciplined RF-referenced frequency comb. By providing ultrastable environmental, mechanical, and vibrational isolation, the overall specifications of the instrument will be sufficient to produce a narrow linewidth (~2 MHz), a reduction in systematic errors to enable up to 1000X increase in accuracy, and a 10X higher count rate to enable precision measurements in manageable measurement durations (months vs years).