Session JT1: Tutorial: Making Cold Antihydrogen from Antimatter Plasmas

Making Cold Antihydrogen from Antimatter Plasmas

The overview, status and recent progress of cold antihydrogen experiments will be presented, with emphasis upon plasma processes and challenges. Both the ATRAP [1,2] and ATHENA [3] have made low energy antihydrogen atoms using antiprotons from CERN's Antiproton Decelerator, and positrons from a radioactive source. The many steps required to trap and form separate non-neutral plasmas of these particles in a Penning-Malmberg trap will be described. Antihydrogen atoms in excited atomic states have been formed by two methods -- during positron-cooling of antiprotons in a nested Penning trap [4] and via 3-body recombination with merged antiproton and positron plasmas, and also by resonant charge exchange of antiprotons and Rydberg positronium [5]. The distribution of excited states and antihydrogen velocities comes from electric-field ionization spectroscopy. Progress toward the goal of forming ground state antihydrogen cold enough ($<<$1 K) to be stored in a magnetic trap will be discussed. A comparison of the spectroscopy of cold, trapped antihydrogen with hydrogen would provide the most precise test of CPT invariance with leptons and baryons. \newline \newline [1] ATRAP, Phys. Rev. Lett. \textbf{89}, 213401 (2002). \newline [2] ATRAP, Phys. Rev. Lett. \textbf{89}, 233401 (2002). \newline [3] ATHENA, Nature \textbf{419}, 456-459, 2002 \newline [4] G. Gabrielse, L. Haarsma, S. Rolston and W. Kells; Physics Letters A $129$, 38 (1988). [5] ATRAP, Phys. Rev. Lett. \textbf{93}, 263401, 2004