Coherence Effects: A Sensitive Tool to Study the Few-Body Dynamics in Simple Atomic Systems

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General audience abstract:Understanding the laws of Nature on a fundamental level is the most important prerequisite for technological development. To this end, two major topics have to be addressed: a) a thorough understanding of the forces acting in Nature needs to be obtained. It is well established that, on an elementary particle level, the mediation of these forces can only occur between two particles at a time. This directly leads to the second topic: b) the description of the evolution of systems consisting of three or more particles under the influence of these pairwise acting forces. This is known as the Few-Body Problem (FBP) in physics and it remains one of the most fundamentally important, and yet unsolved problems in physics. The research supported by this grant aims to advance the understanding of the FBP by studying collision processes between ions and simple atoms or molecules. Such collisions represent systems consisting of a relatively small particle number (typically 3 to 5 particles), which are nevertheless sufficiently complex to be strongly affected by the unsolved FBP. This research will involve several graduate and undergraduate students and prepare them for the scientific and technological needs of society.Technical audience abstract:To address the Few-Body Problem (FBP), the research team will perform kinematically complete experiments on several atomic fragmentation processes. Their interest is focused on two aspects of the few-body dynamics: the importance of higher-order contributions and the role of projectile coherence effects. Until recently, theory focused on perturbative methods in describing such processes. In these models understanding the FBP means accurately describing the contributions of higher-order versus first-order contributions. Their experiments are designed to sensitively test perturbative models and to determine the limitations of such approaches. Regarding the second aspect, prior to recent work by this group and others, theory had assumed that the incoming projectiles are always fully coherent. In studies over the last 8 years the researchers have demonstrated that for heavy particles this is not always a realistic assumption because of the particles' very small deBroglie wavelengths. In the research supported by this grant the research team will use coherence effects as a sensitive tool to study interference effects in greater detail than was possible previously. Interference structures, in turn, usually contain rich information on the few-body dynamics underlying the collision process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.