Few-Body Dynamics in Simple Atomic Systems

理解大大小小的物体是如何移动和相互作用的，对于我们对自然的知识和开发技术是至关重要的。即使是少数物体之间的相互作用也很难理解。物理学中的“少体问题”(FBP)指的是三个或更多物体相互影响彼此的轨迹的情况。这些情景发生在行星和恒星的引力相互作用以及原子、离子和电子的电磁相互作用中。在微观尺度上，量子力学定律也会影响粒子运动。由此产生的动力学很难预测，但对于理解原子碰撞和基本反应可能很重要。这个项目将研究原子-电子-离子散射，以检验关于原子系统中FBP的新理论。特别是，当FBP中的粒子遵守量子力学定律时，波-粒子二象性是重要的。这个项目将研究代表粒子的量子力学波的非局域空间范围或相干长度如何影响粒子相互散射的方式。这将有助于更好地理解反应截面和散射理论。除了原子物理学之外，许多科学领域也与量子力学FBP有关。因此，这项研究涉及科学中广泛的学科，包括核物理、化学物理、等离子体科学和加速器物理。从事这个项目的学生将获得广泛的实验原子物理技术和理论分析方法的研究经验。将进行运动学上完整的实验，涉及两个主要主题。首先，将研究大范围条件下的碰撞反应动力学，包括电子速度接近于弹丸速度的某些区域。第二，将研究与量子力学的一个基本方面有关的投射相干效应。这样的实验同时确定了所有涉及的粒子的动量矢量，即散射体、任何抛射的电子和反冲剩余靶离子。从数据中，反应概率(横截面)将被提取为许多参数的函数。这些数据将为复杂的理论模型提供灵敏的测试，这些模型取决于射束的横向相干长度。为了更好地测试这些模型，将在实验中操纵光束的发散，从而控制射弹的德布罗意波相干性。通过这种方法，我们将研究在带电粒子与原子相互作用中，射束波性质对少体动力学的影响。

Understanding how objects large and small move and interact with each other is essential in our knowledge of nature and in developing technologies. The interactions of even a small number of objects can be challenging to understand. The "few body problem" (FBP) of physics refers to scenarios where three or more objects mutually affect each other's trajectories. These scenarios arise in the gravitational interactions of planets and stars and in the electromagnetic interactions of atoms, ions, and electrons. At the microscopic scale, the laws of quantum mechanics also affect particle motions. The resulting dynamics are challenging to predict, but can be important for understanding atomic collisions and basic reactions. This project will study atom-electron-ion scattering to test new theories about the FBP in atomic systems. In particular, when the particles in the FBP obey the laws of quantum mechanics, then the wave-particle duality is important. This project will investigate how the nonlocal spatial extent, or coherence length, of the quantum mechanical waves that represent the particles can affect the way particles scatter from one another. This will lead to improved understanding of reaction cross sections and scattering theory. Many areas of science well beyond atomic physics are also concerned with the quantum mechanical FBP. Therefore, this research is relevant to a broad range of disciplines in science including nuclear physics, chemical physics, plasma science, and accelerator physics. Students working on this project will gain research experience with a broad range of experimental atomic physics technologies and theoretical analysis methods. Kinematically complete experiments will be performed that address two major themes. First, the reaction dynamics will be investigated for collisions under a broad range of conditions including some regimes with electron speeds close to the projectile speed. Second, projectile coherence effects, which concern a fundamental aspect of quantum mechanics, will be studied. Such experiments simultaneously determine the momentum vectors of all involved particles, i.e. the scattered projectiles, any ejected electron, and the recoiling residual target ions. From the data, reaction probabilities (cross sections) will be extracted as a function of numerous parameters. The data will provide sensitive tests of sophisticated theoretical models that depend on the transverse coherence length of the projectile beams. To better test these models the divergence of the beams, and hence the de Broglie wave coherence for the projectiles, will be manipulated in the experiment. In this way the impact of the projectile wave properties on the few-body dynamics in charged-particle interactions with atoms will be studied.