Probing TeV Physics with neV Neutrons: Precision Measurements of Beta Decays and Electric Dipole Moments

这个奖项所支持的研究活动是为了回答“早期宇宙的性质是什么？”这个基本问题。众所周知，氢、氦和锂是在宇宙大爆炸后不久产生的。然而，大爆炸产生的氦的数量的理论预测高度依赖于自由中子的寿命。最近使用所谓的“瓶子技术”的实验已经达到了破纪录的精度。用不同的技术测量的结果与用瓶子测量的结果相差很大。在这个奖项的支持下，这个PI将通过测量在飞行中衰变的中子束来领导一项中子寿命的新测量。另一个使用氚的衰变实验提供了一种很有希望的方法来确定几乎没有重量的中微子的绝对质量。这个项目精确地测量了氚发生衰变时所发射电子的回旋运动。这为大爆炸核合成提供了另一个关键元素。最后，为了理解为什么大爆炸在宇宙中留下了我们今天所观察到的物质多于反物质的现象，实验室实验正在进行中，以寻找一个关键的线索，即中子内部正负电荷的极小分离。具有广泛背景的学生将在参与这些研究活动的同时获得科学和技术技能的指导。特别是，来自洛斯阿拉莫斯周边较不富裕社区的高中生被邀请参加夏季物理夏令营。伊利诺伊大学厄巴纳-香槟分校核物理组的pi将在实验中子物理和基本对称性测试中开展这些研究活动。工作内容包括：(1)继续UCNtau实验数据采集和分析，同时开发UCNtau+升级版，将中子寿命精度提高到0.1 s。(2)在束流寿命实验方面的合作，通过构建Alpha-Gamma中子校准装置，以解决束流法和瓶法测量的中子寿命值之间10秒的显著差异。(3)利用在UCNtau实验中成功使用的磁引力阱，大量捕获氚原子，为Project-8实验中测量中微子的绝对质量做准备。(4)在LANL准备2023年开始数据采集的中子电偶极矩（nEDM）实验，并在橡树岭散裂中子源继续建设nEDM实验用极化氦-3系统。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The research activities supported by this award are driven by the desire to answer the fundamental question, "What are the properties of the early universe?" It is known that hydrogen, helium, and lithium were produced shortly after the Big Bang. However, theoretical predictions of the amount of helium resulting from the Big Bang are highly dependent on the lifetime of the free neutron. Recent experiments using what is called the “bottle technique” have reached record-breaking precision. Measurements using a different technique differ from the bottle measurements by a surprising amount. With support from this award, this PI will lead a new measurement of the neutron’s lifetime by measuring beam neutrons decaying in flight. Another decay experiment using tritium provides a promising way to determine the absolute mass of the nearly-weightless neutrinos. This project precisely measures the cyclotron motion of the electrons emitted when the tritium undergoes beta decay. This provides another key element of Big-Bang nucleosynthesis. Finally, to understand why the Big Bang left the universe with the surplus of matter over antimatter that we observe today, laboratory experiments are in progress to search for a crucial clue, an extremely small separation of the positive and negative electric charges within the neutron. Students with broad backgrounds will be mentored in scientific and technical skills while participating in these research activities. In particular, high school students from less affluent communities surrounding Los Alamos are invited to participate in summer physics camps.The PIs, in the nuclear physics group at the University of Illinois at Urbana-Champaign, will carry out these research activities in experimental neutron physics and fundamental symmetry tests. The work includes: (1) Continuation of the UCNtau experiment data-taking and analysis, and in parallel, developing the UCNtau+ upgrade to push the neutron lifetime precision towards 0.1 s. (2) Collaboration on the beam-lifetime experiment, by constructing the Alpha-Gamma neutron calibration device, in order to work towards resolving the outstanding 10-second discrepancy between the values of the neutron lifetime measured using the beam and bottle methods. (3) Application of the magneto-gravitational trap, successfully used in the UCNtau experiment, to trap tritium atoms in large numbers in preparation for the measurement the absolute mass of the neutrino in the Project-8 experiment. (4) Preparation of the neutron electric dipole moment (nEDM) experiment at LANL to start data-taking in 2023, and continuing construction of the polarized helium-3 system for the nEDM experiment at the Oak Ridge Spallation Neutron Source.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.