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

这一奖项所支持的研究活动是由回答基本问题的愿望驱动的，这一基本问题是“早期宇宙的性质是什么？”众所周知，氢、氦和锂是在大爆炸后不久产生的。然而，理论上对大爆炸产生的氦气量的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”的实验达到了破纪录的精确度。使用不同技术的测量结果与瓶子的测量结果相差惊人。在该奖项的支持下，这一PI将通过测量飞行中衰减的束流中子来领导对中子寿命的新测量。另一项使用氚的衰变实验提供了一种确定近乎失重的中微子绝对质量的有希望的方法。这个项目精确地测量了氚经历贝塔衰变时发出的电子的回旋运动。这提供了大爆炸核合成的另一个关键元素。最后，为了理解为什么大爆炸给宇宙留下了我们今天观察到的物质超过反物质的盈余，实验室实验正在寻找一条关键的线索，即中子内部极小的正负电荷分离。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方面的指导。特别是，来自洛斯阿拉莫斯周边不太富裕社区的高中生被邀请参加暑期物理夏令营。伊利诺伊大学厄巴纳-香槟分校核物理小组的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。工作包括：(1)继续进行UCNtau实验数据的采集和分析，同时开发UCNtau升级，将中子寿命精度推向0.1.S。(2)通过建造Alpha-Gamma中子定标装置，在束流寿命实验方面进行合作，以努力解决使用束流方法和瓶子方法测量的中子寿命值之间在10秒内存在的突出差异。(3)利用UCNtau实验中成功使用的磁引力陷阱大量俘获氚原子，为Project-8实验测量中微子的绝对质量做准备。(4)准备LANL的中子电偶极矩(NEDM)实验，以于2023年开始数据采集，并继续建造用于橡树岭散裂中子源nEDM实验的极化氦-3系统。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.