Search for Antihelium with the BESS-Polar Spectrometer
Abe, K. · Fuke, H. · Haino, S. · Hams, T. · Hasegawa, M. · Horikoshi, A. · Itazaki, A. · Kim, K. C. · Kumazawa, T. · Kusumoto, A. · Lee, M. H. · Makida, Y. · Matsuda, S. · Matsukawa, Y. · Matsumoto, K. · Mitchell, J. W. · Myers, Z. · Nishimura, J. · Nozaki, M. · Orito, R. · Ormes, J. F. · Sakai, K. · Sasaki, M. · Seo, E. S. · Shikaze, Y. · Shinoda, R. · Streitmatter, R. E. · Suzuki, J. · Takasugi, Y. · Takeuchi, K. · Tanaka, K. · Thakur, N. · Yamagami, T. · Yamamoto, A. · Yoshida, T. · Yoshimura, K.
Original · EN
In two long-duration balloon flights over Antarctica, the BESS-Polar collaboration has searched for antihelium in the cosmic radiation with higher sensitivity than any reported investigation. BESS- Polar I flew in 2004, observing for 8.5 days. BESS-Polar II flew in 2007-2008, observing for 24.5 days. No antihelium candidate was found in BESS-Polar I data among 8.4× 10⁶ |Z| = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0× 10⁷ |Z| = 2 nuclei from 1.0 to 14 GV. Assuming antihelium to have the same spectral shape as helium, a 95% confidence upper limit of 6.9 × 10-8 was determined by combining all the BESS data, including the two BESS-Polar flights. With no assumed antihelium spectrum and a weighted average of the lowest antihelium efficiencies from 1.6 to 14 GV, an upper limit of 1.0 × 10-7 was determined for the combined BESS-Polar data. These are the most stringent limits obtained to date.
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