Few-Body Dynamics in Simple Atomic Systems

了解大大小小的物体是如何移动和相互作用的，这对我们了解自然和发展技术至关重要。即使是少数对象之间的相互作用也很难理解。物理学中的“少体问题”（FBP）是指三个或更多物体相互影响彼此轨迹的情况。这些场景出现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，量子力学定律也影响着粒子的运动。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。本项目将研究原子-电子-离子散射，以验证原子系统中FBP的新理论。特别是，当FBP中的粒子服从量子力学定律时，波粒二象性是重要的。该项目将研究代表粒子的量子力学波的非局部空间范围或相干长度如何影响粒子彼此散射的方式。这将有助于提高对反应截面和散射理论的理解。许多远远超出原子物理学的科学领域也与量子力学的FBP有关。因此，这项研究涉及广泛的科学学科，包括核物理、化学物理、等离子体科学和加速器物理。参与本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。运动学完整的实验将针对两个主要主题进行。首先，研究了在多种条件下的碰撞反应动力学，包括一些电子速度接近弹丸速度的情况。其次，弹丸相干效应，涉及量子力学的一个基本方面，将进行研究。这些实验同时确定了所有相关粒子的动量矢量，即散射的抛射体，任何弹出的电子，以及反冲的剩余目标离子。从数据中，反应概率（横截面）将作为众多参数的函数提取出来。这些数据将为依赖于射束横向相干长度的复杂理论模型提供灵敏的测试。为了更好地测试这些模型，将在实验中控制光束的散度，从而控制抛射体的德布罗意波相干性。通过这种方法，将研究带电粒子与原子相互作用中抛射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.