Search for cosmic-ray antideuteron and antihelium with long duration balloon flight data

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We have searched for cosmic-ray antideuteron and antihelium with BESS-Polar II data. We carefully examined the recovered BESS-PolarII payload from Antarctica and obtained various key information about the detector status during the flight and improved detector performance with the novel calibration method. Based on the data, new searches were performed for antideuteron and antihelium with improved sensitivity by an order of magnitude. No candidates were observed. Null observation of antihelium, together with previous BESS data, placed the most stringent constraint on existence of anti-domain nearby our universe.