Bayesian Analysis of the Hardening in AMS-02 Nuclei Spectra

Abstract

Based on the precise nuclei data released by AMS-02, we study the spectra hardening of both the primary (proton, helium, carbon, oxygen, and the primary component of nitrogen) and the secondary (anti-proton, lithium, beryllium, boron and the secondary component of nitrogen) cosmic ray (CR) nuclei. With the diffusion-reacceleration model, we consider two schemes to reproduce the hardening in the spectra: (i) A high-rigidity break in primary source injection; (ii) A high-rigidity break in diffusion coefficient. The global fitting results show that both schemes could reproduce the spectra hardening in current status. More precise multi-TV data (especially the data of secondary CR species) is needed if one wants to distinguish these two schemes. In our global fitting, each of the nuclei species is allocated an independent solar modulation potential and a re-scale factor (which accounts for the isotopic abundance for primary nuclei species and uncertainties of production cross section or inhomogeneity of CR sources and propagation for secondary nuclei species). The fitting values of these two parameter classes show us some hints on some new directions in CR physics. All the fitted re-scale factors of primary nuclei species have values that systematically smaller than 1.0, while that of secondary nuclei species are systematically larger than 1.0. Moreover, both the re-scale factor and solar modulation potential of beryllium have values which are obviously different from other species. This might indicate that beryllium has the specificity not only on its propagation in the heliosphere, but also on its production cross section. All these new results should be seriously studied in the future.

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

“…The fitting results show that current data set favors a high-rigidity break at ∼ 325 GV in diffusion coefficient rather than a break at ∼ 365 GV in primary source injections, which is consistent with the results obtained in Génolini et al [17]. Moreover, the fitted values of c pri i s (which are the factors to rescale the default isotopic abundances of helium-4, carbon-12, nitrogen-14, and oxygen-16 in galprop) are systematically smaller than 1.0 and consistent with the results in our previous work [16] within fitting uncertainties. While the fitted values of c sec i s (which are the factors to rescale the CR flux of secondary species/components after propagation) are systematically larger than 1.0 and larger than the values obtained in our previous work [16], which includes the entire spectra data points in the global fitting.…”

“…5. For comparison, the corresponding results of our previous work [16], in which the entire AMS-02 nuclei data (including the data points < 50 GV) is used in the global fitting, are shown in the upper panels in Fig. 5.…”

“…2 in Niu et al [16]). In this sense, (ii) and (iii) should have a similar prediction on the spectral hardening in primary and secondary nuclei spectra (see, e.g., Niu et al [16], Feng et al [22]).…”

“…At the same time, some works (see, e.g., Niu and Li [1], Niu et al [16]) show that if one wants to fit the CR secondary spectra successfully, one should employ factors to rescale the flux of them after propagation. For antiproton, this factor is always in the region 0.8-1.9 [1,39,40], and always interpreted as the uncertainties from the antiproton production cross section [41][42][43][44].…”

Combined analysis of AMS-02 (Li,Be,B)/C, N/O, 3He, and 4He data

“…We stress that choosing consistent values for AMS-02 data, Niu et al (2019), i.e. from May 2011 to May 2016.…”