Coherence Effects and Few-Body Dynamics in Atomic Fragmentation Processes

这项工作试图解决以下基本问题。自然界中作用的力是什么？它们的性质是什么？由几个物体组成的系统在这些力的作用下是如何发展的？第二个问题代表了科学中最基本的、尚未解决的问题之一。两个物体的运动通常可以几乎肯定地预测出来。例如，如果太阳系只由太阳和地球组成，人们就可以预测未来任何时候地球相对于太阳的位置和速度。但是，如果只向系统中添加一个对象（如上面的例子中的月球），在我们的数学框架中就不存在解析解（以方程形式给出的解）。这种困境被称为少体问题（FBP）。它对所有自然科学都有非常广泛的影响，因为大多数现代研究都涉及包含两个以上对象的系统。本项目概述了实验研究原子系统的FBP。对于这种微观尺度的系统，量子力学的特性使FBP进一步复杂化，量子力学是设计用来描述这种微小系统的理论。从长远来看，这项工作可能不仅会影响对孤立原子的理解，还会影响原子束（或离子或分子）与表面的相互作用，这是支撑便携式电子设备和计算机制造的关键技术。在这个项目中，将通过对简单目标的离子冲击电离进行运动学完整实验来研究少体问题。直接测量了抛射体的动量矢量和反冲目标离子的动量矢量，并根据运动守恒定律推导出抛射电子的动量。从数据中提取全微分截面（FDCS）。通过改变放置在目标前的准直狭缝的几何形状，可以改变射弹的相干性。直到最近才发现FDCS对弹丸相干长度敏感。反过来，这可以解释理论和实验之间非常令人困惑的差异，这是过去十年来激烈辩论的问题。本文旨在系统地探讨弹丸相干性在原子少体系统中的作用。预计这些研究的结果将是朝着彻底理解少体问题迈出的重要一步。

This work seeks to address the following basic questions. What are the forces acting in nature and what are their properties? How do systems consisting of several objects develop under the influence of these forces? The second question represents one of the most fundamental, unsolved problems in science. The motion of two objects can often be predicted with virtual certainty. For example, if the solar system consisted of only the sun and the earth, one could predict the position and the velocity of the earth relative to the sun for all times in the future. But if only one more object is added to the system (say the moon in the above example) no analytic solution (one that is given in terms of equations) within our mathematical framework exists. This dilemma is known as the few-body problem (FBP). It has very broad impacts in all of the natural sciences because most of modern research deals with systems containing more than 2 objects. The project outlined in this proposal experimentally studies the FBP for atomic systems. For such systems of microscopic scale the FBP is further complicated by the characteristics of quantum-mechanics, the theory that was designed to describe such tiny systems. In the long term, this work may influence not only the understanding of isolated atoms, but also the interaction of beams of atoms (or ions or molecules) with surfaces, something which is a key technology underpinning the manufacturing of portable electronic devices and computers.In this project the few-body problem will be studied by performing kinematically complete experiments on ionization of simple targets by ion impact. The momentum vectors of the scattered projectiles and of the recoiling target ions are measured directly and the momentum of the ejected electron is deduced from the kinematic conservation laws. From the data, fully differential cross sections (FDCS) will be extracted. The coherence properties of the projectile can be varied by changing the geometry of a collimating slit placed before the target. Only relatively recently it was discovered that the FDCS can be sensitive to the projectile coherence length. This, in turn, can explain very puzzling discrepancies between theory and experiment, which were vividly debated for the last decade. The proposed work aims at systematically exploring the role of the projectile coherence properties in atomic few-body systems. It is anticipated that the results from these studies will represent an important step forward towards a thorough understanding of the few-body problem.