Precision Measurement of the Positron Fraction in Primary Cosmic Rays with AMS on the Space Station

The AMS-02 experiment is a large acceptance spectrometer continuously operating onboard the International Space Station since May 2011. One of the main objectives of the AMS-02 mission is the measurement of the rare antimatter components of cosmic rays. In six years of operations, AMS-02 has detected 20 million cosmic ray electrons and positrons that have been used to precisely measure the positron fraction – the ratio of positrons over the sum of positrons and electrons – in cosmic rays from 0.5 GeV to 700 GeV. The analysis of the latest data collected by AMS-02 extends the energy range of the previous measurement and improves its precision.