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.
