First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5-350 GeV

• Main Authors: Basil, A. (Contributor), Becker, R. (Contributor), Becker, Ulrich J. (Contributor), Behlmann, Matthew Daniel (Contributor), Berges, P. (Author), Burger, Joseph D. (Contributor), Cai, X. D. (Author), Capell, Michael H. (Contributor), Chen, Andrew I. (Contributor), Chen, H. (Contributor), Choumilov, Evgueni (Contributor), Choutko, Vitali (Contributor), Dennett, P. (Contributor), Egorov, A. (Contributor), Eline, Alexandre (Contributor), Eppling, Frederic J. (Contributor), Fisher, Peter H. (Contributor), Flood, Kevin T. (Contributor), Galaktionov, Y. (Contributor), Gallilee, M. (Contributor), Gargiulo, C. (Contributor), Goglov, Pavel (Contributor), Hungerford, W. (Contributor), Incagli, M. (Contributor), Koulemzine, A. (Contributor), Kounina, Olga (Contributor), Kounine, Andrei (Contributor), Koutsenko, Vladimir (Contributor), Krafczyk, Matthew Scott (Contributor), Lebedev, Ilia A. (Contributor), Plyaskin, V. (Contributor), Rozhkov, A. (Contributor), Schinzel, D. (Contributor), Steuer, V. (Contributor), Sun, W. (Contributor), Ting, Samuel C. C. (Contributor), Ting, S. M. (Contributor), Titus, Christine (Contributor), Vaurynovich, Siarhei S. (Contributor), Vergain, M. (Contributor), Wang, X. (Contributor), Willenbrock, M. (Contributor), Zuccon, Paolo (Contributor), P. Berges (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science (Contributor), Massachusetts Institute of Technology. Department of Physics (Contributor), Massachusetts Institute of Technology. Laboratory for Nuclear Science (Contributor), Cai, X.D (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2013-09-30T16:14:56Z.
• Subjects: Article
• Online Access: Get fulltext

 A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8×10[superscript 6] positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ∼250  GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.