BESS (Balloon-borne Experiment with a Superconducting Spectrometer) is a U.S.-Japan program that uses elementary particle measurements to study the early universe. BESS measures the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic sources, and it searches for heavier antinuclei that might reach Earth from antimatter domains formed during symmetry-breaking processes in the early universe.
The BESS-Polar instrument was developed for long-duration balloon flights over Antarctica. Both BESS and BESS-Polar are the largest balloon-borne magnet instruments
BESS-Polar I flew for 8.5 days in 2004—at a transient period prior to solar minimum—and reported 1,512 antiprotons. BESS-Polar II recorded data with the magnet energized for 24.5 days in 2007–2008, flying at solar minimum, when the sensitivity of the antiproton measurements to a low-energy primary component is greatest, and is expected to have detected ~ 10,000 antiprotons. The instrument performed very well, and collected 13.5 terabytes of data. BESS-Polar II landed on the West Antarctic Ice Sheet in January 2008. Although the data was collected in February of 2008, the instrument has been sitting on the ice sheet for two years until now.
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