Theory of Atomic Structure and Processes

这项提议的统一主题是通过将高*精度理论和实验结合起来应用于原子来开发新的测量工具。简而言之，理论方面的基础是我们对氦和锂等原子的基本精确的非相对论*波函数，以及相对论和量子电动力学*效应的最新技术。然后，与实验的比较为了解新的物理现象提供了一个窗口。过去授权期*的一个主要例子是利用原子跃迁频率中的同位素位移来推断氦-6*和氦-8等奇异“晕核”的大小和形状。原子和核物理之间的界面工作是与世界上最顶尖的实验小组*在高能粒子加速器上合作完成的，这些高能粒子加速器包括Argonne(美国)、GSI(德国)和TRIUMF(加拿大)。基于加速器的*项目在获得批准之前要经过严格的可行性和重要性标准。*未来的工作将以我们过去的经验为基础，并在几个方向上加以扩展。首先，我们开发的同位素位移方法现在被公认为测量晕核大小的最准确的方法，在许多情况下也是唯一可用的方法。这些奇异的结构有额外的行星中子围绕着一个由中子和质子组成的紧密结合的核心。这些结果的*意义在于，它们使人们能够区分为将原子核保持在一起的有效*力而提出的各种理论模型。通过研究容易解体的结构，我们了解了将它们结合在一起的力量。*我们之前在氦、锂和铍的晕核方面的工作将与德国GSI的实验小组合作，扩展到硼。同位素元素周期表中正在出现引人入胜的趋势。*第二，我们正在开辟一个新的研究领域，应用于寻找超越基本*粒子物理标准模型的新物理。当晕核通过弱相互作用衰变时，它同时发射出一个β粒子(高能电子)和一个中微子。标准模型预测了两个出射粒子之间的夹角，任何偏离该角度的情况都将标志着标准模型之外的新物理现象。我们目前正在计算在解释测量结果时必须考虑的原子电子的反冲贡献。我们的初步结果表明，与1963年具有里程碑意义的实验存在严重分歧。目前迫切需要新的实验工作和进一步的计算，以考虑到在贝塔衰变过程中被“甩掉”的原子电子。这项工作是与华盛顿大学的一个实验小组正在进行的合作。*其他拟议的工作重点是原子理论和量子电动力学的基础测试。**

The unifying theme of this proposal is the development of new measurement tools through the combined application of both high***precision theory and experiment to atoms. In brief, the theoretical side rests on a foundation of our essentially exact nonrelativistic***wave functions for atoms such as helium and lithium, combined with the state-of-the-art for relativistic and quantum electrodynamic***effects. A comparison with experiment then provides a window into new physical phenomena. A prime example from the past grant period***is the use of the isotope shift in atomic transition frequencies to deduce the size and shape of exotic "halo" nuclei such as helium-6***and helium-8. This work at the interface between atomic and nuclear physics is done in collaboration with the top experimental groups***in the world at high energy particle accelerators such as Argonne (U.S.), GSI (Germany) and TRIUMF (Canada). The accelerator-based***projects are subjected to rigorous standards of feasibility and significance before being approved.***Future work will build on our past experience and extend it in several directions. First, the isotope shift method developed by***us is now well recognized as the most accurate method, and in many cases the only method available, to measure the size of***halo nuclei. These exotic structures have extra planetary neutrons surrounding a tightly bound core of neutrons and protons. The***significance of the results is that they enable one to distinguish among the various theoretical models proposed for the effective***forces holding the nucleus together. By studying structures that fall apart easily, we learn about the forces holding them together.***Our previous work on the halo nuclei of helium, lithium and beryllium will next be extended to boron, in collaboration with experimental groups at GSI, Germany. Fascinating trends are emerging across the periodic table of isotopes.***Second, we are opening up a new area of study with applications to search for new physics beyond the standard model of elementary***particle physics. When a halo nucleus decays via the weak interaction, it emits both a beta-particle (high energy electron) and a neutrino. The standard model predicts the angle between the two outgoing particles, and any deviation from it would signal new physics beyond the standard model. We are currently calculating the recoil contribution due to the atomic electrons that must be taken into account in interpreting the measurements. Our preliminary results indicate that there is a serious disagreement with a landmark 1963 experiment. There is an urgent need for both new experimental work and further calculations that take into account the atomic electrons that are "shaken off" following the beta decay process. This work is an ongoing collaboration with an experimental group at the University of Washington.***Other proposed work focuses on fundamental tests of atomic theory and quantum electrodynamics.**