Deciphering the Local Interstellar Spectra of Secondary Nuclei with the Galprop/Helmod Framework and a Hint for Primary Lithium in Cosmic Rays

Abstract

Local interstellar spectra (LIS) of secondary cosmic ray (CR) nuclei, lithium, beryllium, boron, and partially secondary nitrogen, are derived in the rigidity range from 10 MV to ∼200 TV using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. The lithium spectrum appears somewhat flatter at high energies compared to other secondary species that may imply a primary lithium component. Two propagation packages, GALPROP and HELMOD, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HELMOD, which provides the modulated spectra for specific time periods of the selected experiments for the model-data comparison. The proposed LIS accommodate the low-energy interstellar spectra measured by Voyager 1, HEAO-3, and ACE/CRIS as well as the high-energy observations by PAMELA, AMS-02, and earlier experiments that are made deep in the heliosphere. The interstellar and heliospheric propagation parameters derived in this study are consistent with our earlier results for propagation of CR protons, helium, carbon, oxygen, antiprotons, and electrons.

Galactic halo size in the light of recent AMS-02 data

“…Using AMS-02 Be/B data we find L = 5 +3 −2 kpc at 1σ, in agreement with Boschini et al (2020) (but with a larger error) Fig. 5.…”

“…Using updated cross sections and propagating their uncertainties, we find here L = 5 +3 −2 kpc based on AMS-02 Be/B data, which is now compatible with values derived from ACE-CRIS 10 Be/ 9 Be data. Similar values were found by the GALPROP team, using both ACE-CRIS and AMS-02 Be fluxes (without 10 Be/ 9 Be), with L = 4 ± 0.6 kpc (Boschini et al 2020). This stronger constraint is somehow in line with the fact that combining ACE-CRIS and AMS-02 data lead to tighter constraints (see Table 3), but as these authors do not use 10 Be/ 9 Be, it is most probably attributed to a larger extent to the fact that they do not propagate cross-section uncertainties.…”

“…This stronger constraint is somehow in line with the fact that combining ACE-CRIS and AMS-02 data lead to tighter constraints (see Table 3), but as these authors do not use 10 Be/ 9 Be, it is most probably attributed to a larger extent to the fact that they do not propagate cross-section uncertainties. In any case, the value of L with a small error inferred in Boschini et al (2020) is also in mild tension with the recent analysis of AMS-02 Be data in Evoli et al (2020), where a best-fit value of L = 7 kpc but a lower limit L 5 kpc is found in a semi-analytical model similar to the one used here. Their central value, using total or statistical uncertainties only, is always enclosed within our 1σ confidence interval: firstly, the difference with our best-fit value is possibly due to their cross-section parametrisation (Evoli et al 2019), as illustrated in Fig.…”

Some new hints on cosmic-ray propagation from AMS-02 nuclei spectra

“…[53] If it is the case, one needs extra injection of secondary nuclei species in high energy region. This scenario is recently studied by some interesting works (see, e.g., Yang and Aharonian [54] and Boschini et al [55]).…”

The role of systematic uncertainties on our understanding of cosmic-ray diffusion: An analysis of AMS-02 data from Lithium to Oxygen

“…Historically, B and the B/C ratio have been the most investigated nuclei to constrain cosmic-ray (CR) propagation. Nonetheless, the precise CR data in a large energy range between 1 GeV and a few TeV provided by AMS-02 [1] have triggered a great number of new studies [2][3][4][5][6][7][8][9]. We perform global fits of CR propagation models to the published AMS-02 data of CR secondaries Li, Be, and B [10], the primaries C and O [11], and the mixed secondary and primary N [12].…”