Collaborative Research: Experimental and Theoretical Study of the Plasma Physics of Antihydrogen Generation and Trapping

去年，反氢粒子第一次被欧洲核子研究中心的ALPHA合作项目捕获。到目前为止，数百个反原子被捕获的时间是1000秒的几倍。虽然这是一项了不起的成就，但ALPHA装置的配置并不适合大多数反氢性质的测量，必须重建以允许激光和更好的微波访问。此外，捕获率虽然足以开始研究反物质的性质，但仍低于最佳水平。提高捕获率面临两大挑战：(1)理解合成反氢的正电子和反质子等离子体的行为；(2)了解正电子和反质子重组的原子过程。反氢合成处于原子物理和等离子体物理的边界上，如果不使用这两个领域的工具，就不能进行适当的研究。反氢研究的长期目标是寻找氢和反氢性质之间的差异。这种差异可能发生在两个物种的光谱之间。光谱上的差异只能由CPT违和引起。另一个可能出现差异的地方是氢和反氢的引力相互作用。这种差异可以解决重子发生的问题。电位差的第三个方面是反氢的分数电荷。相对于单位电荷，反氢的净电荷仅为10^-7。任何这些测量的积极结果都将彻底改变我们对基本粒子和基本场的理解。物理问题将通过在CERN的实验、经典轨迹蒙特卡罗、分子动力学、3D PIC代码和解析理论进行研究。将要解决的一些问题包括：实现改进的（更低的）轻子和反质子温度；研究轻子与背景辐射场的相互作用；研究轻子与谐振腔的相互作用；改进血浆诊断；并且改进了正电子和反质子的混合，这样更多的反氢可以被保存在一个非常浅的中性阱中。虽然寻找这些问题答案的动机来自反氢研究，但其中许多问题在等离子体和原子物理学中提出了新颖而深刻的问题。这项研究的长期目标是解决我们理解周围世界的基础问题。它潜在地对粒子相互作用的本质、物质-反物质对称问题和宇宙学有着深远的影响。与此同时，这项研究是独一无二的，因为反物质的研究对公众来说是容易接近和吸引人的。去年反氢的捕获在非专业和科学媒体上得到了非常广泛的关注。反氢实验非常简单，研究生可以完全理解它们。因此，他们为学生提供了广泛的教育。实验人员学习束流和等离子体物理、实验规划和设计、仪器、特高压实践、电子学、低温学、磁学和软件开发。随着理论的发展，理论学家可以对实验的设计、操作和分析做出重要贡献。材料的相对可及性使得本科生很容易融入实验和理论课程。拟议的研究包括代表性不足的群体成员的大量参与。

Last year, antihydrogen was trapped for the first time by the ALPHA collaboration at CERN. By this point hundreds of antiatoms have been trapped for times as long as 1000 s. While this was a remarkable achievement, the ALPHA apparatus is not well configured for most measurements of the properties of antihydrogen, and must be rebuilt to allow laser and better microwave access. Furthermore, the trapping rates, while sufficient to begin studies of the properties of antimatter, are lower than optimal. There are two broad challenges to improving the trapping rate: (1) Understanding the behavior of the positron and antiproton plasmas from which the antihydrogen is synthesized; and (2) Understanding the atomic processes by which positrons and antiprotons recombine. Antihydrogen synthesis lies on the boundary between atomic and plasma physics, and cannot be studied properly without employing tools from both fields. The long term goal of antihydrogen research is to search for differences between the properties of hydrogen and antihydrogen. Such differences might occur between the spectra of the two species. Differences in the spectra could only result from CPT violation. Another place differences might occur is in the gravitational interactions of hydrogen and antihydrogen. Such differences could solve the baryogenesis problem. A third area of potential difference is in the fractional charge of antihydrogen. The net charge of antihydrogen is only known to about 10^-7 relative to the unit charge. Positive results from any of these measurements would completely change our understanding of fundamental particles and fields. The physics issues will be studied with experiments at CERN, with classical trajectory Monte Carlo, molecular dynamics, and 3D PIC codes, and with analytic theory. Some of the questions that will be addressed include: achieving improved (lower) lepton and antiproton temperatures; studying how leptons interact with the background radiation field; studying how leptons interact with resonant cavities; improved plasma diagnostics; and improved mixing of positrons and antiprotons, so that more of the resultant antihydrogen can be held in a very shallow neutral trap. While the motivation for seeking answers to these questions comes from antihydrogen research, many of these questions raise novel and deep issues in plasma and atomic physics. The long-¬term goals of this research address the very basis of our understanding of the world around us. Potentially, it has deep implications on the nature of particle interactions, on the question of matter-¬antimatter symmetry, and on cosmology. At the same time, this research is uniquely visible because the study of antimatter is accessible and fascinating to the public. The trapping of antihydrogen last year was extraordinarily widely noted in the lay and scientific press. Antihydrogen experiments are sufficiently simple that they can be comprehended in their entirety by graduate students. Consequently, they offer students a broad education. Experimentalists learn beam and plasma physics, experimental planning and design, instrumentation, UHV practice, electronics, cryogenics, magnetics and software development. Along with theory development, theorists can make critical contributions to the design, operation, and analysis of the experiments. The relative accessibility of the material makes it easy to integrate undergraduate students into both the experimental and theoretical program. The proposed research includes significant participation by members of underrepresented groups.