Search for Antihelium with the BESS-Polar Spectrometer

• Main Authors: Matsumoto, K., Mitchell, J. W., Fuke, H., Ormes, J. F., Matsuda, S., Horikoshi, A., Hams, T., Nishimura, J., Kumazawa, T., Matsukawa, Y., Seo, E. S., Sasaki, M., Nozaki, M., Myers, Z., Lee, M. H., Kusumoto, A., Orito, R., Makida, Y., Haino, S., Abe, K., Hasegawa, M., Sakai, K., Itazaki, A., Streitmatter, R. E., Kim, K. C.
• Format: Other/Unknown Material
• Language: unknown
• Published: 2012
• Subjects: Physics (General); Antarc*; Antarctica
• Online Access: http://hdl.handle.net/2060/20120009359

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. BESSPolar 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 x 10(exp 6) [Z] = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0 x 10(exp 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 x 10(exp -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 x 10(exp -7) was determined for the combined BESS-Polar data. These are the most stringent limits obtained to date.