Using the updated proton and helium fluxes just released by the Ams-02 experiment we reevaluate the secondary astrophysical antiproton to proton ratio and its uncertainties, and compare it with the ratio preliminarly reported by Ams-02. We find no unambiguous evidence for a significant excess with respect to expectations. Yet, some preference for a flatter energy dependence of the diffusion coefficient (with respect to the Med benchmark often used in the literature) starts to emerge. Also, we provide a first assessment of the room left for exotic components such as Galactic Dark Matter annihilation or decay, deriving new stringent constraints. *

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 convectionreacceleration model where transport is tuned by non-relativistic effects. All models lead to robust predictions in the high-energy regime ( 10 GV), i.e. independent of the propagation scenario: at 1σ, the diffusion slope δ is [0.43 − 0.53], whereas K10, the diffusion coefficient at 10 GV, is [0.26 − 0.36] kpc 2 Myr −1 ; we confirm the robustness of the high-energy break, with a typical value ∆ h ∼ 0.2. We also find a hint for a similar (reversed) feature at low rigidity around the B/C peak (∼ 4 GV) which might be related to some effective damping scale in the magnetic turbulence. CONTENTS 7 4. The fitting procedure 8 IV. Results 8 A. Best-fit values and 1σ uncertainties 8 B. Possible interpretation and microphysics 10 C. Robustness of low-, intermediate-, and high-rigidity parameters 10 V. Summary, conclusions, and perspectives 11 Acknowledgments 11 A. On the high-rigidity break from C, O and the fitting procedure 11 1. Consistency check 12 2. Break vs no-break 13 B. Fit parameters dependence upon low-rigidity cutoff 13 C. Scaling of propagation parameters with L in 1D model 13 arXiv:1904.08917v2 [astro-ph.HE]