Spectroscopy of positronium molecules and Bose-Einstein Condensates

正电子，化学符号为Ps，是氢原子的一种非常轻的形式，由一个电子和一个反电子或正电子组成。由等量的物质和反物质组成，正电子最长的基态在湮灭成三个光子之前只存在七分之一微秒。然而，这种短暂的存在对于研究正电子原子的致密气体的性质来说是足够长的。这项研究将使用稠密的正电子气体来研究双正电子分子PS2和正电子玻色-爱因斯坦凝聚。在美国国家科学基金会仪器计划资助(DMR-0216927)的帮助下开发的一台仪器将为该项目提供包含约1亿个正电子的短脉冲。正电子将聚焦在由多孔性固体组成的靶面上，正电子原子在其中形成的几率很高。目标将包含一个微小的掩埋腔，100万个正电子原子将聚集到一个密度，使正电子玻色-爱因斯坦凝聚应该在高达20K的温度下发生。为了观察这些效应，脉冲激光系统将发射紫外光，能够激发正电子和PS2莱曼-阿尔法，或基态到第一激发态的跃迁。尽管ps腔在填充正电子原子的普通气体时对紫外光是透明的，但当原子凝聚时，腔将变得不透明，从而使首次观察到正电子玻色-爱因斯坦凝聚成为可能。该项目的更广泛影响包括学生培训以及与当地高中的联系。

Positronium, with the chemical symbol Ps, is a very light form of hydrogen atom consisting of an electron and an anti-electron, or positron. Being composed of equal amounts of matter and antimatter, the longest-lived ground state of positronium lives for only one seventh of a microsecond before annihilating into three photons. Nevertheless, this transient existence is long enough for studying the properties of a dense gas of positronium atoms. This research will employ a dense positronium gas to investigate di-positronium molecules, Ps2, and positronium Bose-Einstein condensation. An apparatus developed with the assistance of an NSF Instrumentation program grant (DMR-0216927) will provide this project with short pulses containing about 100 million positrons. The positrons will be focused on a target surface composed of a porous solid in which positronium atoms form with high probability. The target will contain a tiny buried cavity into which one million positronium atoms will collect to a density such that positronium Bose-Einstein condensation should occur at temperatures as high as 20K. To observe these effects, a pulsed laser system will deliver ultra-violet light capable of exciting the positronium and Ps2 Lyman-alpha, or ground-state to first excited state, transitions. Although a Ps cavity would be transparent to the ultra-violet light when filled with an ordinary gas of positronium atoms, the cavity will become opaque when the atoms condense, thus enabling the first observations of positronium Bose-Einstein condensation. The broader impact of the program involves student training as well as outreach to the local high school.