Antiproton Flux, Antiproton-to-Proton Flux Ratio, and Properties of Elementary Particle Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

Abstract

A precision measurement by AMS of the antiproton flux and the antiproton-to-proton flux ratio in primary cosmic rays in the absolute rigidity range from 1 to 450 GV is presented based on $3.49 \times 10^5$ antiproton events and $2.42 \times 10^9$ proton events. The fluxes and flux ratios of charged elementary particles in cosmic rays are also presented. In the absolute rigidity range ~60 to ~500 GV, the antiproton $ \bar{p} $,proton $p$ , and positron $e^{+}$ fluxes are found to have nearly identical rigidity dependence and the electron $e^-$ flux exhibits a different rigidity dependence. Below 60 GV, the ($\bar{p}/p$), ($\bar{p}/e^-$), and ($p/e^{+}$) flux ratios each reaches a maximum. From ~60 to ~500 GV, the ($\bar{p}/p $), ($\bar{p}/e^+ $), and ($\bar{p}/e^+ $) flux ratios show no rigidity dependence. These are new observations of the properties of elementary particles in the cosmos.

 

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Table-SM-I

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The antiproton flux $\Phi^{\bar p}$ and the antiproton/proton flux ratio $\Phi^{\bar p}/\Phi^{p}$ as a function of absolute rigidity at the top of AMS. $\tilde{N}^{\bar p}$ is the number of antiprotons observed in each rigidity bin rounded to the nearest integer. $\sigma_{\rm stat}$ and $\sigma_{\rm syst}$ are the respective statistical and systematic errors.

Table-SM-II

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The antiproton-to-positron flux ratio $\Phi^{\bar p}/\Phi^{e^+}$ and the antiproton-to-electron flux ratio $\Phi^{\bar p}/\Phi^{e^-}$ as a function of rigidity at the top of AMS. $\sigma_{\rm stat}$ are the statistical errors on the ratios, $\sigma_{\rm syst}$ are the systematic errors on the ratios, and $\sigma_{\rm scale}$ are the errors from the energy scale uncertainty in $\Phi^{e^\pm}$. The antiproton flux binning is used.

Table-SM-III

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The proton-to-positron flux ratio $\Phi^{p}/\Phi^{e^+}$ and the proton-to-electron flux ratio $\Phi^{p}/\Phi^{e^-}$ as a function of rigidity at the top of AMS. $\sigma_{\rm stat}$ are the statistical errors on the ratios, $\sigma_{\rm syst}$ are the systematic errors on the ratios, and $\sigma_{\rm scale}$ are the errors from the energy scale uncertainty in $\Phi^{e^\pm}$. The proton flux binning is used.

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