K. Abe, H. Fuke, S. Haino, T. Hams, M. Hasegawa, A. Horikoshi, A. Itazaki, K. C. Kim, T. Kumazawa, A. Kusumoto, M. H. Lee, Y. Makida, S. Matsuda, Y. Matsukawa, K. Matsumoto, J. W. Mitchell, Z. Myers, J. Nishimura, M. Nozaki, R. Orito, J. F. Ormes, K. Sakai, M. Sasaki, E. S. Seo, Y. Shikaze, R. Shinoda, R. E. Streitmatter, J. Suzuki, Y. Takasugi, K. Takeuchi, K. Tanaka, N. Thakur, T. Yamagami, A. Yamamoto, T. Yoshida, K. Yoshimura
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\times
10^6 |Z| = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0\times
10^7 |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 \times 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 \times
10^-7 was determined for the combined BESS-Polar data. These are the most
stringent limits obtained to date.
View original:
http://arxiv.org/abs/1201.2967
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