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

摘要：在基本层面上理解自然规律是技术发展最重要的先决条件。为此，必须解决两个主要问题：a)需要获得对自然界中起作用的力的透彻理解。很显然，在基本粒子水平上，这些力的中介作用一次只能发生在两个粒子之间。这直接引出了第二个主题：b)描述在这些成对作用力的影响下由三个或更多粒子组成的系统的演化。这在物理学中被称为少体问题（FBP），它仍然是物理学中最重要的，但尚未解决的问题之一。该基金支持的研究旨在通过研究离子与简单原子或分子之间的碰撞过程来促进对FBP的理解。这种碰撞代表了由相对较小的粒子数（通常为3到5个粒子）组成的系统，然而，这些系统足够复杂，因此受到未解决的FBP的强烈影响。这项研究将涉及几名研究生和本科生，并使他们为社会的科学和技术需求做好准备。摘要：为了解决少体问题（FBP），研究团队将对几个原子破碎过程进行运动学完整实验。他们的兴趣集中在少体动力学的两个方面：高阶贡献的重要性和弹丸相干效应的作用。直到最近，理论集中在描述这些过程的微扰方法上。在这些模型中，理解FBP意味着准确地描述高阶贡献与一阶贡献。他们的实验旨在灵敏地测试微扰模型，并确定这种方法的局限性。关于第二个方面，在这个小组和其他人最近的工作之前，理论假设入射的弹丸总是完全连贯的。在过去8年的研究中，研究人员已经证明，对于重粒子，这并不总是一个现实的假设，因为粒子的德布罗意波长非常小。在这项资助的研究中，研究小组将使用相干效应作为一种灵敏的工具，比以前更详细地研究干涉效应。干涉结构，反过来，通常包含丰富的信息，在碰撞过程下的少体动力学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.