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J. F. Ormes (NASA/GSFC), U. Tokyo BESS Collaboration, High Energy Accelerator Research Organization (KEK) BESS Collaboration, NASA/GSFC BESS Collaboration, Kobe U. BESS Collaboration, U. Maryland BESS Collaboration, Institute of Space and Astronautical Science BESS Collaboration
The energy spectra of cosmic-ray antiprotons, protons and helium nuclei have been measured using the Balloon-borne Superconducting Solenoidal (BESS) magnetic rigidity spectrometer. More than 1600 antiproton events have been accumulated on annual flights since 1993. Instrumental improvements have been made yearly. We have detected the peak at 2 GeV expected from cosmic-ray interactions with the interstellar gas. The simultaneous measurement of the proton and helium spectra is essential in showing that model propagation calculations, independently constrained, reproduce the measurements, implying that the propagation models are basically correct. The most recent upper limit for the anti-helium/helium ratio, below 10-6, will be presented. An accompanying paper will discuss the implications of these measurements for the search for evidence of decaying primordial black holes and dark matter in the galactic halo. The data analysis was performed using computing facilities at ICEEP at the U. of Tokyo. The experiment was supported by a Grant-in-Aid for Scientific Research in Monbusho, Heiwa Nakajima Foundation in Japan and by NASA in the US.