The following report is from a February 1996 article in the Encarta Yearbook.

Antimatter Atoms Created for the First Time

The European Laboratory for Particle Physics (CERN) in Switzerland and France announced on January 4, 1996, that a multinational team of scientists had succeeded in producing atoms of antimatter. Antimatter is believed to be identical to matter in its physical properties, but its constituent particles have electromagnetic properties that are the opposite of corresponding particles of matter. The team included physicists from the Jülich Institute for Nuclear Physics Research and the University of Münster in North Rhine-Westfalia, Germany; the University of Genoa in Italy; the University of Erlangen-Nuremberg in Bavaria, Germany; and GSI, a physics research center in Darmstadt, Germany.

Scientists have created, examined, and used smaller particles of antimatter—specifically, antielectrons and antiprotons—in experiments for decades. Never before, however, have these particles been manipulated in such a way that they have combined to form whole atoms of antimatter.

The European team of scientists created antihydrogen, the simplest antiatom possible. Normal hydrogen consists of one proton and one electron. To make antihydrogen, the team combined an antielectron (also called a positron) with an antiproton. Positrons have the same mass and amount of charge as electrons, but electrons have a negative charge and positrons have a positive charge. Similarly, antiprotons have the same mass and amount of charge as protons, but antiprotons have a negative charge and protons have a positive charge.

The CERN team detected nine atoms of antihydrogen over a three-week period in September 1995. Each particle existed for about 40 billionths of a second before colliding with ordinary matter, at which point the antiatom and a corresponding portion of the matter that it contacted were converted into a pulse of energy. This mutual destruction, called annihilation, occurs whenever antimatter comes into contact with matter.

To create the antiatoms, the physicists first slowed antiprotons created in high-energy collisions in CERN particle accelerators. They then diverted the antiprotons to the center's Low Energy Antiproton Ring (LEAR), a tube in which the antiprotons, directed by electromagnetic fields, whirled around about three million times per second. The physicists shot a jet of xenon gas through one point on the ring, so that some of the antiprotons would collide with the large, inert atoms of xenon. Sometimes the energy of the collisions would create an electron and a positron from the antiproton. In a few cases, the path of a positron and an antiproton would be such that they would combine to form an atom of antimatter.

The atoms of antihydrogen, like atoms of hydrogen, had no net electrical charge and therefore were not influenced by the electromagnetic fields of the LEAR. As soon as they formed, they flew off the path of the ring, were separated back into a positron and an antiproton, and collided with ordinary matter after traveling about 10 m (33 ft).

Physicists hope to soon be able to keep antiatoms in existence long enough to begin studying the properties of antimatter and determine if it behaves in the same way as ordinary matter. Other than the recently synthesized antihydrogen, antimatter atoms have never been detected in the universe. Theory predicts that antimatter should behave exactly as ordinary matter, each particle influencing the other in the same interplay of forces that is seen with ordinary matter. In addition, theoretical physics can suggest no reason why matter should be more common than antimatter in the universe. Any variations in the behavior of antimatter atoms may provide physicists with clues as to why the universe appears devoid of antimatter.

In addition to the team represented at CERN, centers that are participating in efforts to create, slow, and trap antihydrogen for study include Pennsylvania State University, Harvard University, Stanford University, the Los Alamos National Laboratory, and the Fermi National Laboratory in the United States; and the Max Planck Institute for Quantum Optics in Germany.

The positron was first discovered by the American physicist Carl Anderson in 1932, a few years after its existence was predicted by the equations of British theoretical physicist Paul Dirac. Antiprotons were first detected in 1955 by the American physicists Owen Chamberlain and Emilio Segrè.

Source: Encarta Yearbook, February 1996.

Appears in

Antimatter; Antiparticles