Because of its instability, antimatter is notoriously hard to handle. Fast-moving or "hot" antimatter has been created for years, but previous hot anti-atoms were annihilated by collisions with matter before they could be studied. Last year the ATRAP (for Antihydrogen Trap) team led by Gerald Gabrielse of Harvard University, announced they'd pioneered methods of slowing down negatively charged antiprotons and combining them with slow positrons, the positively charged antimatter equivalent of electrons, to yield the simplest possible anti-atom: antihydrogen.
Now the team has made the first measurements of a complete antihydrogen atom. The ATRAP team took their hard-won anti-atoms and ripped them apart with an electric field. Gabrielse explains "it's like putting the anti-atom next to a battery. The antiproton would be attracted to one terminal and the positron would be drawn to the opposite one." The researchers tweak the electric field until the atom is torn asunder; the strength of the field required indicates how tightly the anti-atom was held together. Their article describing the results will appear in Physical Review Letters in November.
These first measurements don't indicate a difference in the way antihydrogen and hydrogen are put together, but Gabrielse says to detect differences they'll need to measure anti-atoms in a more "normal" state. Although the anti-atoms they've studied move slowly, their positrons are still excited to unusually high levels. The researchers' next step is to "de-excite" the anti-atoms so they can make comparisons to the physics of normal hydrogen atoms.
According to Gabrielse, almost everyone expects the properties of hydrogen and antihydrogen to be the same. Detecting differences, he says, would be "the biggest discovery in physics in decades" that would "require scientists to reformulate the most basic laws of physics".
Current theories predict that the universe could just as easily be made of antimatter as of matter and don't explain why our universe is made up exclusively of the latter. If the researchers find small differences in the properties of matter and antimatter, they would contradict the present paradigm and might help solve the riddle. NSF program manager Denise Caldwell from the Division of Physics says the ATRAP work is "the critical first experiment in the search for differences between matter and antimatter using antihydrogen."
Gabrielse doesn't expect the study of anti-atoms to yield new applications, but he points out that their cutting-edge studies have produced technology that improves everyday life. Magnetic traps used to hold antiparticles are now used in analyzing pharmaceuticals, and the superconducting magnets they've patented can be used in magnetic imaging. As Gabrielse puts it, "If you push reality really hard, good things always come out of it."
The National Science Foundation has sponsored the research leading up to this seminal experiment for 15 years. Gabrielse is joined in his efforts by ATRAP team members from Harvard University, the Forschungszentrum Jülich, CERN, the Max-PlanckInstitut für Quantenoptik in Garching, the Ludwig-MaximiliansUniversität in Munich and York University.
For more about the ATRAP collaborative effort, see: http://hussle.
NSF PR 02-88