Properties of a New Group of Cosmic Nuclei: Results from the Alpha Magnetic Spectrometer on Sodium, Aluminum, and Nitrogen

Phys. Rev. Lett. 127, 021101 (2021)
Published on:
Abstract

We report the properties of sodium (Na) and aluminum (Al) cosmic rays in the rigidity range 2.15 GV to 3.0 TV based on 0.46 million sodium and 0.51 million aluminum nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. We found that Na and Al, together with nitrogen (N), belong to a distinct cosmic ray group. In this group, we observe that, similar to the N flux, both the Na flux and Al flux are well described by the sums of a primary cosmic ray component (proportional to the silicon flux) and a secondary cosmic ray component (proportional to the fluorine flux). The fraction of the primary component increases with rigidity for the N, Na, and Al fluxes and becomes dominant at the highest rigidities. The Na/Si and Al/Si abundance ratios at the source, $0.036 \pm 0.003$ for Na/Si and $0.103 \pm 0.004$ for Al/Si, are determined independent of cosmic ray propagation.

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The Na flux as a function of rigidity at the top of AMS in units of $[{\rm m}^2 \cdot {\rm sr} \cdot {\rm s} \cdot {\rm GV}]^{-1}$ including errors due to statistics (stat.); contributions to the systematic error from the trigger and acceptance (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic error.

The Al flux as a function of rigidity at the top of AMS in units of $[{\rm m}^2 \cdot {\rm sr} \cdot {\rm s} \cdot {\rm GV}]^{-1}$ including errors due to statistics (stat.); contributions to the systematic error from the trigger and acceptance (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic error.

The sodium to silicon flux ratio $\Phi_{\rm Na}/\Phi_{\rm Si}$ as a function of rigidity including errors due to statistics (stat.); contributions to the systematic error from the trigger, acceptance, and background (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The statistical errors are the sum in quadrature of the ratios of sodium and silicon flux statistical errors to the corresponding flux values, multiplied by $\Phi_{\rm Na}/\Phi_{\rm Si}$. The systematic errors from the background subtraction, the trigger, and the event reconstruction and selection are likewise added in quadrature. The correlations in the systematic errors from the uncertainty in nuclear interaction cross sections, the unfolding and the absolute rigidity scale between the sodium and silicon fluxes have been taken into account in calculating the corresponding systematic errors of $\Phi_{\rm Na}/\Phi_{\rm Si}$. The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic uncertainty.

The aluminum to silicon flux ratio $\Phi_{\rm Al}/\Phi_{\rm Si}$ as a function of rigidity including errors due to statistics (stat.); contributions to the systematic error from the trigger, acceptance, and background (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The statistical errors are the sum in quadrature of the ratios of aluminum and silicon flux statistical errors to the corresponding flux values, multiplied by $\Phi_{\rm Al}/\Phi_{\rm Si}$. The systematic errors from the background subtraction, the trigger, and the event reconstruction and selection are likewise added in quadrature. The correlations in the systematic errors from the uncertainty in nuclear interaction cross sections, the unfolding and the absolute rigidity scale between the aluminum and silicon fluxes have been taken into account in calculating the corresponding systematic errors of $\Phi_{\rm Al}/\Phi_{\rm Si}$. The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic uncertainty.

The sodium to fluorine flux ratio $\Phi_{\rm Na}/\Phi_{\rm F}$ as a function of rigidity including errors due to statistics (stat.); contributions to the systematic error from the trigger, acceptance, and background (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The statistical errors are the sum in quadrature of the ratios of sodium and fluorine flux statistical errors to the corresponding flux values, multiplied by $\Phi_{\rm Na}/\Phi_{\rm F}$. The systematic errors from the background subtraction, the trigger, and the event reconstruction and selection are likewise added in quadrature. The correlations in the systematic errors from the uncertainty in nuclear interaction cross sections, the unfolding and the absolute rigidity scale between the sodium and fluorine fluxes have been taken into account in calculating the corresponding systematic errors of $\Phi_{\rm Na}/\Phi_{\rm F}$. The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic uncertainty.

The aluminum to fluorine flux ratio $\Phi_{\rm Al}/\Phi_{\rm F}$ as a function of rigidity including errors due to statistics (stat.); contributions to the systematic error from the trigger, acceptance, and background (acc.); the rigidity resolution function and unfolding (unf.); the absolute rigidity scale (scale); and the total systematic error (syst.). The statistical errors are the sum in quadrature of the ratios of aluminum and fluorine flux statistical errors to the corresponding flux values, multiplied by $\Phi_{\rm Al}/\Phi_{\rm F}$. The systematic errors from the background subtraction, the trigger, and the event reconstruction and selection are likewise added in quadrature. The correlations in the systematic errors from the uncertainty in nuclear interaction cross sections, the unfolding and the absolute rigidity scale between the aluminum and fluorine fluxes have been taken into account in calculating the corresponding systematic errors of $\Phi_{\rm Al}/\Phi_{\rm F}$. The contribution of individual sources to the systematic error are added in quadrature to arrive at the total systematic uncertainty.

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