Taming Dirac's Particle

The birth of the positron (the antiparticle of the electron) and the concept of antimatter through Paul Dirac’s theoretical work some 80 years ago enable a wealth of scientific and technological opportunities. Much progress has been made recently in developing new tools to exploit them. Described here are examples of new techniques and the science that has resulted. Electromagnetic traps are used to accumulate positrons efficiently, to cool them, and to tailor the resulting collections of antiparticles. These usually volatile antiparticles can then be stored for long periods, as necessary, and used in specific applications. Large magnetic fields are used to induce radiative cooling. A combination of electric and magnetic fields is employed to increase antiparticle densities and to tailor the resulting single-component antimatter plasmas. Other techniques have been developed to produce tailored antiparticle beams, and efforts are underway to build traps for much larger collections of antimatter. We describe here some of these developments and the science that has resulted. As an example, positrons can bind to atoms and molecules. Novel features of these transient states are described. While the resulting positive ions last only a few nanoseconds, they provide insights into the rich behavior of antiparticles in our world of matter. The implications of these studies for the behavior of positrons in various environments, including astrophysical settings and materials, will be discussed. These results will be placed in the more general context of efforts to develop the principles of a chemistry of antimatter and matter.