Coherence Effects and Few-Body Dynamics in Atomic Fragmentation Processes

这项工作试图解决以下基本问题。自然界中的力是什么，它们的性质是什么？由多个物体组成的系统如何在这些力的影响下发展？第二个问题代表了科学中最基本、最悬而未决的问题之一。通常可以几乎确定地预测两个物体的运动。例如，如果太阳系只由太阳和地球组成，人们就可以在未来的所有时间预测地球相对于太阳的位置和速度。但是，如果只有一个物体被添加到系统中(比如上面例子中的月球)，在我们的数学框架内就不存在解析解(以方程形式给出的解析解)。这种两难境地被称为少体问题(FBP)。它在所有自然科学中都有非常广泛的影响，因为大多数现代研究涉及的是包含两个以上物体的系统。该提案中概述的项目对原子系统的FBP进行了实验研究。对于这种微观尺度的系统，量子力学的特性使FBP变得更加复杂，量子力学理论是为描述这种微小系统而设计的。从长远来看，这项工作不仅可能影响对孤立原子的理解，还可能影响原子束(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，将通过对简单目标离子碰撞电离的运动学完整实验来研究少体问题。直接测量了散射体和反弹靶离子的动量矢量，并由运动守恒定律推导出抛射电子的动量。从数据中提取出全差分截面(FDCs)。通过改变放置在目标前面的准直狭缝的几何形状，可以改变射弹的相干特性。直到最近，人们才发现FDCS对弹丸相干长度很敏感。这反过来又可以解释理论和实验之间令人费解的差异，这些差异在过去十年里被生动地辩论过。这项拟议的工作旨在系统地探索入射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了解少数人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.