Precision Measurements with Cold and Ultracold Neutrons

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。研究项目包括几个研究项目，在这些项目中，使用极低能中子来加强我们对基本相互作用的理解。在第一个项目中，研究了中子β衰变中的几个观测值；这些观测值与另一个实验结果(中子寿命的确定)相结合，确定了导致中子衰变的弱相互作用的耦合常数。它们被用作对当前理论有效性的灵敏测试，该理论描述了核子与轻子(中子衰变产生的电子和中微子)之间的弱相互作用。一个相关的过程是核子与其他核子之间的弱耦合，第二个项目是测量质子俘获中子中伽马射线发射方向相对于中子极化的不对称性，以确定核子之间弱相互作用的主导过程的强度。第三个项目是描述玻璃镜上方引力场中超冷中子的引力束缚量子态。一系列实验被用来寻找影响这些量子态的新的短程相互作用。最后，将为氦-4建造一个净化器，作为超冷中子的生产目标，以寻找中子的电偶极矩。氦-3污染必须远低于自然丰度，以避免超冷中子对氦-3杂质的重新声明。这个实验计划的共同目标是在以前无法访问的区域测试标准模型，或者至少不是那么精确。标准模型中没有解释的东西的发现将对高能物理和宇宙学产生重要影响。此外，这些实验具有很高的教育潜力：除了在科学上可见和技术上具有挑战性的项目上工作的优势外，美国和国际机构在中等规模的合作中教授的职业伦理对学生来说都非常有价值，无论是作为未来的科学家还是学术界以外的人。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The research projects covers several research projects in which very low energy neutrons are used to strengthen our understanding of fundamental interactions. In the first project, several observables in neutron beta decay are studied; the combination of these observables with another experimental result (the determination of the neutron lifetime) determines the coupling constants of the weak interaction which causes the neutron decay. They are used as a sensitive test of the validity of the present theory which describes weak interaction coupling nucleons to leptons (the electrons and neutrinos produced in neutron decay). A related process is the weak coupling between nucleons and other nucleons, and the second project, a measurement of the asymmetry in the direction of gamma ray emission relative to the polarization of a neutron in the neutron capture on protons, is performed to determine the strength the dominant process of the weak interaction between nucleons. The third project is the characterization of gravitationally bound quantum states of ultracold neutron in the gravitational field over a glass mirror. A series of experiments is used to search for new short range interactions which would influence these quantum states. Finally, a purifier will be built for Helium-4 which is used as a production target for ultracold neutrons in a search for the electric dipole moment of the neutron. The Helium-3 contamination has to be reduced far below the natural abundance to avoid the reassertion of the ultracold neutrons on Helium-3 impurities.The common goal of this experimental program is to test the Standard Model in regions which were not accessible before, or at least not as precise. A discovery of something not explained in the Standard Model would have important implications for High Energy Physics and Cosmology. Additional, the experiments have a high educational potential: Besides the advantages of working on scientifically visible and technologically challenging projects, the work ethics taught in medium-size collaborations of US and international institutions is of great value to students, be it as future scientist or outside academia.