Few-Body Dynamics in Simple Atomic Systems

了解大小物体如何移动和相互作用对我们了解自然和开发技术至关重要。 即使是少量对象的交互也可能很难理解。 物理学中的“少体问题”（英语：few body problem）是指三个或三个以上的物体相互影响彼此的轨迹。 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，量子力学定律也会影响粒子的运动。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很重要。本计画将研究原子-电子-离子的散射，以验证原子系统中关于FBP的新理论。特别是，当FBP中的粒子服从量子力学定律时，波粒二象性就很重要。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。这将导致更好的理解反应截面和散射理论。原子物理学以外的许多科学领域也与量子力学的FBP有关。因此，这项研究与广泛的科学学科有关，包括核物理，化学物理，等离子体科学和加速器物理。从事该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进行，解决两个主要问题。首先，反应动力学将在广泛的条件下，包括一些制度的电子速度接近弹丸速度的碰撞进行调查。其次，将研究与量子力学的一个基本方面有关的射弹相干效应。这样的实验同时确定了所有相关粒子的动量矢量，即散射的射弹、任何射出的电子和反冲的残余靶离子。从数据中，反应概率（横截面）将被提取为众多参数的函数。这些数据将提供复杂的理论模型，取决于横向相干长度的弹丸光束的敏感测试。为了更好地测试这些模型，将在实验中操纵光束的发散度，从而操纵射弹的布罗意波相干性。通过这种方法，我们将研究带电粒子与原子相互作用中入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.