Precision measurement of antiproton to proton ratio with the Alpha Magnetic Spectrometer on the International Space Station

A precision measurement by AMS of the antiproton-to-proton flux ratio in primary cosmic raysin the absolute rigidity range from 1 to 450 GV is presented based on 3.49×10^5 antiproton eventsand 2.42×10^9 proton events. Above ∼60 GV the antiproton to proton flux ratio is consistentwith being rigidity independent. A decreasing behaviour is expected for this ratio considering thetraditional models for the secondary antiproton flux.