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Register a new userSpatial Dependent Diffusion of Cosmic Rays and the Excess of Primary Electrons Derived from High Precision Measurements by AMS-02
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The precise spectra of Cosmic Ray (CR) electrons and positrons have been published by the measurement of AMS-02. It is reasonable to regard the difference between the electrons and positrons spectra ( $triangle Phi= Phi_{e^-}-Phi_{e^+}$ ) as being dominated by primary electrons. Noticing that the resulting electron spectrum shows no sign of spectral softening above 20 GeV, which is in contrast with the prediction of standard model. In this work, we generalize the analytic one dimensional two-halo model of diffusion to a three dimensional realistic calculation by implementing a spatial variant diffusion coefficients in DRAGON package. As a result, we can reproduce the spectral hardening of protons observed by several experiments, and predict an excess of high energy primary electrons which agrees with the measurement reasonably well. Unlike the break spectrum obtained for protons, the model calculation predicts a smooth electron excess and thus slightly over predicts the flux from tens of GeV to 100GeV. To understand this issue, further experimental and theoretical studies are necessary.
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The AMS-02 collaboration has just released its first result of the cosmic positron fraction $e^+/(e^-+e^+)$ with high precision up to $sim 350$ GeV. The AMS-02 result shows the same trend with the previous PAMELA result, which requires extra electron/positron sources on top of the conventional cosmic ray background, either from astrophysical sources or from dark matter annihilation/decay. In this paper we try to figure out the nature of the extra sources by fitting to the AMS-02 $e^+/(e^-+e^+)$ data, as well as the electron and proton spectra by PAMELA and the $(e^-+e^+)$ spectrum by Fermi and HESS. We adopt the GALPROP package to calculate the propagation of the Galactic cosmic rays and the Markov Chain Monte Carlo sampler to do the fit. We find that the AMS-02 data have implied essential difference from the PAMELA data. There is {rm tension} between the AMS-02 $e^+/(e^-+e^+)$ data and the Fermi/HESS $(e^-+e^+)$ spectrum, that the AMS-02 data requires less contribution from the extra sources than Fermi/HESS. Then we redo the fit without including the Fermi/HESS data. In this case both the pulsars and dark matter annihilation/decay can explain the AMS-02 data. The pulsar scenario has a soft inject spectrum with the power-law index $sim 2$, while the dark matter scenario needs $tau^+tau^-$ final state with mass $sim 600$ GeV and a boost factor $sim 200$.
Cosmic-ray antiprotons are a remarkable diagnostic tool for the study of astroparticle physics processes in our Galaxy. While the bulk of measured antiprotons is consistent with a secondary origin, several studies have found evidence for a subdominant primary component in the AMS-02 data. In this proceedings article, we revisit the excess considering systematic errors that could affect the signal. Of particular importance are unknown correlations in the AMS-02 systematic errors, the dominant of which are associated with the cross sections for cosmic-ray absorption in the detector. We compute their correlations in a careful reevaluation of nuclear scattering data, utilizing the Glauber-Gribov theory to introduce a welcomed redundancy that we explore in a global fit. The inclusion of correlated errors has a dramatic effect on the significance of the signal. In particular, the analysis becomes more sensitive to the diffusion model at low rigidities. For a minimal extension beyond single-power-law diffusion, the global significance drops below 1$sigma$ severely questioning the robustness of the finding.
Several studies have pointed out an excess in the AMS-02 antiproton spectrum at rigidities of 10-20 GV. Its spectral properties were found to be consistent with a dark-matter particle of mass 50-100 GeV which annihilates hadronically at roughly the thermal rate. In this work, we reinvestigate the antiproton excess including all relevant sources of systematic errors. Most importantly, we perform a realistic estimate of the correlations in the AMS-02 systematic error which could potentially fake a dark-matter signal. The dominant systematics in the relevant rigidity range originate from uncertainties in the cross sections for absorption of cosmic rays within the detector material. For the first time, we calculate their correlations within the full Glauber-Gribov theory of inelastic scattering. The AMS-02 correlations enter our spectral search for dark matter in the form of covariance matrices which we make publicly available for the cosmic-ray community. We find that the global significance of the antiproton excess is reduced to below 1 $sigma$ once all systematics, including the derived AMS-02 error correlations, are taken into account. No significant preference for a dark-matter signal in the AMS-02 antiproton data is found in the mass range 10-10000 GeV.
This article aims at establishing new benchmark scenarios for Galactic cosmic-ray propagation in the GV-TV rigidity range, based on fits to the AMS-02 B/C data with the USINE v3.5 propagation code. We employ a new fitting procedure, cautiously taking into account data systematic error correlations in different rigidity bins and considering Solar modulation potential and leading nuclear cross-section as nuisance parameters. We delineate specific low, intermediate, and high-rigidity ranges that can be related to both features in the data and peculiar microphysics mechanisms resulting in spectral breaks. We single out a scenario which yields excellent fits to the data and includes all the presumably relevant complexity, the BIG model. This model has two limiting regimes: (i) the SLIM model, a minimal diffusion-only setup, and (ii) the QUAINT model, a convection-reacceleration model where transport is tuned by non-relativistic effects. All models lead to robust predictions in the high-energy regime ($gtrsim10$GV), i.e. independent of the propagation scenario: at $1sigma$, the diffusion slope $delta$ is $[0.43-0.53]$, whereas $K_{10}$, the diffusion coefficient at 10GV, is $[0.26-0.36]$kpc$^2$Myr$^{-1}$; we confirm the robustness of the high-energy break, with a typical value $Delta_hsim 0.2$. We also find a hint for a similar (reversed) feature at low rigidity around the B/C peak ($sim 4$GV) which might be related to some effective damping scale in the magnetic turbulence.
In this work, we considered 2 schemes (a high-rigidity break in primary source injections and a high-rigidity break in diffusion coefficient) to reproduce the newly released AMS-02 nuclei spectra (He, C, N, O, Li, Be, and B) when the rigidity larger than 50 GV. The fitting results show that current data set favors a high-rigidity break at $sim 325 mathrm{GV}$ in diffusion coefficient rather than a break at $sim 365 mathrm{GV}$ in primary source injections. Meanwhile, the fitted values of the factors to rescale the cosmic-ray (CR) flux of secondary species/components after propagation show us that the secondary flux are underestimated in current propagation model. It implies that we might locate in a slow diffusion zone, in which the CRs propagate with a small value of diffusion coefficient compared with the averaged value in the galaxy. Another hint from the fitting results show that extra secondary CR nuclei injection may be needed in current data set. All these new hints should be paid more attention in future research.
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