Balloon-Borne Instrument Collects Antimatter

It wasn't science fiction, but cutting-edge science. Carrying a Japanese-built instrument, NASA's largest balloon -- 39 million cubic feet in volume -- lifted off from Lynn Lake, Manitoba, Canada, at 9:22 a.m. EDT Aug. 11 for a 38-hour flight more than 20 miles above Earth. The 5,000-pound instrument was recovered Aug. 12 and will be prepared for another flight next year. The BESS project (Balloon-borne Experiment with a Superconducting Solenoidal magnet), led by Prof. Shuji Orito of the University of Tokyo, is sponsored in the U.S. by NASA and by Monbusho in Japan.

Antiparticles are rare forms of matter that have electrical charges exactly the opposite of their ordinary "sister" particles. For example, a proton has a positive charge and an electron has a negative charge. An antiproton, though, has a negative charge and an antielectron has a positive charge. Scientists study antimatter to understand structure and energy processes in the Universe.

"We have collected excellent data, which should contain several hundred antiprotons among a hundred million cosmic-ray particles that passed through our detector," said Dr. Orito, who was at Lynn Lake for the launch with researchers from Japan and the United States.

Although many theorists believe that the entire Universe is made of "ordinary" matter, some speculate that antimatter galaxies exist. However, no evidence of these galaxies has been found. Previous balloon flights have detected numerous anti-protons, but these can be produced by collisions of "ordinary" particles in interstellar space.

If BESS were to find a more sophisticated form of antimatter, such as molecules of anti-helium, it would provide evidence that antimatter galaxies exist. Unlike antiprotons, anti-helium is virtually impossible to create by collision and would have to come from some other source.

"The discovery of anti-helium would be stunning," said Dr. Orito. "That is why we search for such exotic objects, although there exist no compelling reasons to believe that anti-galaxies do exist. We have actually found no anti-helium in data taken during the five flights from 1993 to 1998, while we have detected three million helium nuclei. This fact provides the most direct evidence that the Galaxy and the nearby part of the Universe are made solely of matter, not antimatter."

The detection of anti-helium would rewrite the books on cosmology, according to Dr. Jonathan Ormes, head of the Laboratory of High Energy Astrophysics at NASA's Goddard Space Flight Center in Greenbelt, MD. "The idea that large regions or domains of the Universe might be built of antimatter has been discussed for many years," said Dr. Ormes, one of many scientists involved in data analysis. "We are very excited every year when we check the latest data hoping to find the first 'Ambassador from the Anti-World.'"

"BESS illustrates the beauty of scientific ballooning," said Dr. W. Vernon Jones, Senior Science Program Executive at NASA Headquarters. "The instrument's capacity has improved dramatically since it was first flown in 1993, when it made the first unambiguous detection of cosmic antiprotons. After each flight the BESS team improves the instrument for the next flight, resulting in a steadily increasing number of detections. This capability coupled with low costs demonstrates an advantage of balloon flights over satellites for this type of research."

The BESS collaboration comprises University of Tokyo, High Energy Accelerator Research Organization, Kobe University and Institute of Space and Astronautical Science, all in Tokyo; NASA Goddard Space Flight Center, Greenbelt, MD; and the University of Maryland. The magnet and the detectors on BESS were designed and constructed in Japan. NASA provides the balloon flights. Aside from antiprotons, BESS also measures precise energy spectra of various cosmic rays, such as protons, helium and light isotopes, thus providing important basic data for cosmic-ray physics. Dr. Eun-Suk Seo of the University of Maryland leads this effort.