BESS-Polar Long Duration Flights in Antarctica

A long-duration balloon flight in Antarctica is being prepared. Known as BESS-Polar, it aims at extremely sensitive measurement of low energy antiprotons to search for any novel primary origin and to study the cosmic-ray propagation and the solar modulation. The search for cosmic antimatter is a fundamental objective to study baryon asymmetry/symmetry in the Universe. The BESS experiment having an excellent rigidity resolution and large geometrical acceptance will maximize the advantage of long duration flights in Antarctica where the rigidity cut- off is very low. A very compact and thin superconducting magnet spectrometer is being developed to maximize the BESS-Polar scientific return. The progress and further plan is described.