Antimatter Atomic Physics -- Walters 330 (6005): 762 -- Science

Antimatter Atomic Physics -- Walters 330 (6005): 762 -- Science: At the European Centre for Nuclear Research (CERN), there are four major collaborations (ALPHA, ATRAP, AEGIS, and ASACUSA) trying to make very slow (very "cold") antihydrogen (9), the bound state of an antiproton and a positron (see the figure). The purpose is to test the fundamental CPT symmetry of relativistic quantum mechanics—inverting charge, parity, and time—and whether matter and antimatter behave in the same way in a gravitational field (10). There are major problems, such as how to make antihydrogen sufficiently cold, how to trap such a neutral species, and how to obtain it in its lowest energy state. At present, antihydrogen has been formed only in very highly excited states.

Cloaking effect in atoms baffles scientists - physics-math - 04 November 2010 - New Scientist

Cloaking effect in atoms baffles scientists: "Laricchia's team fired positronium atoms at 1100 to 4400 kilometres per second into various gases, including hydrogen, krypton and water vapour. Curiously, the scattering rates for positronium were almost identical to that of a plain electron, as though the positron's influence was somehow 'cloaked'.

James Walters, a theorist at Queen's University Belfast who studies matter-antimatter interactions, says the result will be tough to explain mathematically because the scattering process is so complex."