BESS-Polar: long duration flights at antarctica to search for primordial antiparticles

Abstract The BESS-Polar experiment with long-duration balloon flights at Antarctica aims at extremely sensitive measurement of low energy antiprotons to search for novel primary origins in the early Universe, and to study cosmic-ray propagation and solar modulation. The search for cosmic antimatter is a fundamental objective to study baryon asymmetry in the Universe. The BESS experiment with high rigidity resolution and large geometrical acceptance will maximize advantages of long duration flights at Antarctica where the rigidity cut-off is lowest. A very compact and thin superconducting magnet spectrometer is being developed to maximize the detector performance in low energies. The BESS-Polar project and progress of the development are described.