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

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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.