Speaker
Description
We present the precision measurement of daily proton and helium fluxes in cosmic rays from May 20, 2011 to November 1, 2025 in the rigidity interval from 1.71 to 100 GV collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The proton and helium fluxes, and the helium to proton flux ratio exhibit variations on multiple timescales. In nearly all the time intervals from 2014 to 2018, we observed recurrent proton and helium flux variations with a period of 27 days. In the entire time period, we found that below ∼7 GV the helium flux exhibits larger time variations than the proton flux, and above ∼7 GV the helium to proton flux ratio is time independent. Remarkably, below 2.4 GV a hysteresis between the helium to proton flux ratio and the helium flux was observed at greater than the 7𝜎 level. This shows that at low rigidity the modulation of the helium to proton flux ratio is different before and after the solar maximum.
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