Abstract
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 positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to , 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.
- Received 14 March 2013
DOI:https://doi.org/10.1103/PhysRevLett.110.141102
© 2013 American Physical Society
Viewpoint
Positrons Galore
Published 3 April 2013
The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays.
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