Fermilab Antihydrogen Experiment Fact Sheet

Experimenters at Fermi National Accelerator Laboratory announced at the Laboratory’s weekly All-Experimenters’ Meeting on November 18, 1996, that they had begun to detect atoms of antihydrogen produced in a gas-jet target in the Fermilab Antiproton Accumulator.

By Thursday, November 21, Fermilab Experiment E866, “The Search for Antihydrogen,” had detected seven antihydrogen atoms, the simplest atoms of antimatter. When the experiment begins optimal operation, scientists at Fermilab expect to detect about five antimatter atoms per day, for a total of several hundred by the end of the current experimental run.

The Fermilab experiment confirms the results announced in January 1996 by scientists at CERN, the European Laboratory for Particle Physics. Physicists there produced a total of nine atoms of antihydrogen before the CERN experiment ended its run.

Antihydrogen atoms consist of an antiproton and an associated antielectron or positron. Both the CERN and Fermilab antihydrogen experiments use an idea first proposed by physicists Charles Munger, Ivan Schmidt, and Stanley Brodsky at a conference in Munich in July, 1992. An Antiproton that passes an atomic nucleus with sufficient speed can create an electron-positron pair; in rare instances, the positron will stick to the moving antiproton to make an atom of antihydrogen. Fermilab’s higher-intensity and higher-energy antiproton source allow greater antihydrogen detector rates than CERN could achieve.

Fundamental precepts of the scientific theory known as quantum field theory require that atoms of antihydrogen exhibit the same atomic spectrum as atoms of hydrogen. Tests of this fundamental precept are theoretically possible, but would require thousands of atoms of antimatter. The CERN and Fermilab experiments are steps toward the ability to produce sufficient quantities of antihydrogen to permit such tests.

Key to the success of the Fermilab experiment is its gas-jet target, which uses a design developed by Italian scientists Mario Macri and Mauro Marinelli at the University of Genoa. Antiprotons from the Antiproton Source strike the target and produce a tiny number of atoms of antihydrogen.

The seven-member Fermilab collaboration, a small one by high-energy physics standards, includes physicists from Fermilab, and the University of California at Irvine.

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