Search for Antihelium with the BESS-Polar Spectrometer

• Main Authors: 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.
• Format: Text
• Language: unknown
• Published: arXiv 2012
• Subjects: Cosmology and Nongalactic Astrophysics astro-ph.CO; FOS Physical sciences; Antarc*; Antarctica
• Online Access: https://dx.doi.org/10.48550/arxiv.1201.2967; https://arxiv.org/abs/1201.2967

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. : 4 pages, 4 figures