The AMS-02 cosmic ray deuteron flux is consistent with a secondary origin

TL;DR

This study shows that cosmic ray deuterons can be explained as secondary particles produced by heavy nuclei fragmentation, aligning with AMS-02 data without requiring primary deuteron sources, thus resolving previous astrophysical challenges.

Contribution

The paper demonstrates that heavy nuclei fragmentation accounts for the observed deuteron flux, challenging the need for primary deuteron sources and aligning with recent cosmic ray measurements.

Findings

Secondary deuterons from heavy nuclei fragmentation match AMS-02 data.

No primary deuteron component is necessary to explain observations.

Differences in D and 3He spectra are due to energy conversion and solar modulation.

Abstract

The recent measurements of cosmic ray deuteron fluxes by AMS-02 show that the rigidity dependence of deuterons is similar with that of protons but flatter than $^3$He, which has been attributed to the existence of primary deuterons with abundance much higher than that from the Big Bang nucleosynthesis. The requirement of highly deuteron-abundant sources imposes a serious challenge on the modern astrophysics since there is no known process to produce a large amount of deuterons without violating other constraints \citep{1976Natur.263..198E}. In this work we demonstrate that the fragmentation of heavy nuclei up to nickel plays a crucial role in shaping/enhancing the spectrum/flux of the cosmic ray deuterons. Based on the latest cosmic ray data, the predicted secondary fluxes of deuterons and $^3$He are found to be reasonably consistent with the AMS-02 measurements and a primary deuteron component is not needed. The observed differences between the spectra of D and $^3$He, as well as those between the D/$^4$He (D/p) and $^3$He/$^4$He ($^3$He/p) flux ratios, measured in the rigidity space, is probably due to the kinetic-energy-to-rigidity conversion and the solar modulation, given different charge-to-mass ratios of D and $^3$He. More precise measurements of the fragmentation cross sections of various nuclei to produce deuterons, tritons, and $^3$He in a wide energy range will be very helpful in further testing the secondary origin of cosmic ray deuterons.