Precision Measurement of 1S-2S Interval in Positronium

该项目将提高正电子素（Ps）原子光谱的准确性。光谱学很重要，因为原子吸收的光的颜色（或“光谱”）是一种独特的指纹，可用于医学，国防和工业中广泛应用的化学识别。光谱学还可以揭示亚原子粒子及其基本相互作用的细节。 Ps是用于此目的的唯一原子。 Ps是由一个电子与一个反电子（正电子）结合形成的。 由于Ps不包含任何质子或中子，Ps原子的光谱学是对束缚态量子电动力学（现代原子物理学的基石理论）的一个很好的测试。 因此，该项目将促进科学的进步。 该项目还将通过培训来自不同背景的学生开发和实施高精度光谱技术来帮助扩大国家的高科技劳动力。纯轻子正电子素（Ps）原子是唯一非常适合测试束缚态量子电动力学（QED）的原子。 万亿分之几的高精度Ps光谱学将提供背景信息，可用于从较重轻子和强子的精确原子测量中提取非QED物理。 这样一来，Ps光谱学就可以揭示质子电荷半径之谜。 它还可以帮助限制μ介子中更高水平的反冲效应修正。先前由coPI和S.朱棣文已经站了25年。 测量中的不确定性来自正电子素原子在激光束中花费的时间太少（渡越时间加宽），原子移动太快（二阶多普勒频移），激光强度太高（AC斯塔克频移），以及计量限制在~1 MHz水平。 该项目将采用几种新技术来提高准确度和精确度。位置敏感的飞行时间探测器将记录每个被探测原子通过较大激光束轮廓时的轨迹和速度，从而减少由于二阶多普勒频移、AC斯塔克频移和渡越时间加宽而引起的不确定性。采用频率梳和拍频技术，监测电子偶素原子通过激发光束时的瞬时激光频率。 这些创新应将测量的不确定性降低300倍，目标是达到10 kHz的不确定性。 这项工作将培养研究生在原子物理学，正电子科学，激光光谱学和计量学的组合。这种培训将有利于学生以及国家提供高技能的博士学位。是为科学工作者准备的UCR是教育部指定的西班牙裔服务机构（HSI），30%的物理专业学生和15%的研究生来自代表性不足的少数民族群体。几位本科生研究人员和一位高中教师也将参与这些实验，这将有助于吸引更多的参与者进入STEM学科。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。

This project will improve the accuracy of positronium (Ps) atom spectroscopy. Spectroscopy is important because the colors of light (or "spectrum") absorbed by atoms is a unique fingerprint that is useful for chemical identification in a broad range of applications found in medicine, defense, and industry. Spectroscopy can also reveal details about sub-atomic particles and their fundamental interactions. Ps is a unique atom for this purpose. Ps is formed by an electron bound with an anti-electron (positron). Because Ps does not contain any protons or neutrons, spectroscopy of Ps atoms is an excellent test of bound-state quantum electrodynamics, a cornerstone theory for modern atomic physics. This project will thus promote the progress of science. This project will also help expand the nation's high technology work force by training students from diverse backgrounds to develop and implement high precision spectroscopy techniques.The purely leptonic positronium (Ps) atom is uniquely well-suited for testing bound-state quantum electrodynamics (QED). High accuracy Ps spectroscopy at the few parts per trillion level will provide background information that can be used to extract non-QED physics out of precision atomic measurements with heavier leptons and hadrons. In this way, Ps spectroscopy can shed light on the proton charge radius puzzle. It can also help constrain higher level recoil effect corrections in muonium. The previous precision measurement of the Ps 1S-2S interval, 1,233,607,216.4 +/- 3.2 MHz, performed by the coPI and S. Chu has stood for 25 years. The uncertainty in this measurement came from positronium atoms spending too little time in the laser beam (transit time broadening), atoms moving too fast (second-order Doppler shift), laser intensity too high (AC Stark shift), and metrology limited at the ~1 MHz level. This project will implement several new techniques to improve accuracy and precision. A position-sensitive time-of-flight detector will record the trajectory and speed of every detected atom as it passes through a larger laser beam profile, and thereby reduce the uncertainty due to second-order Doppler shifts, AC Stark Shifts, and transit-time broadening. A frequency-comb and a frequency-beat technique will be used to monitor the instantaneous laser frequency as positronium atoms transit the excitation beam. These innovations should reduce the uncertainty in the measurement by a factor of 300, with the goal of reaching a 10 kHz uncertainty. This work will train graduate students in a combination of atomic physics, positron science, laser spectroscopy, and metrology. This training will benefit the students as well as the Nation by providing highly skilled Ph.D.'s for the scientific workforce. UCR is a Department of Education Designated Hispanic Serving Institution (HSI) with 30% of Physics majors and 15% of graduate students from under-represented ethnic minority groups. Several undergraduate researchers and a high school teacher will also be involved in these experiments, and this will help to attract more participants to STEM disciplines.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.