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

Abstract

Context. The vertical diffusive halo size of the Galaxy, L, is a key parameter for dark matter indirect searches. It can be better determined thanks to recent AMS-02 data.
Aims: We set constraints on L from Be/B and ¹⁰Be/Be data, and we performed a consistency check with positron data. We detail the dependence of Be/B and ¹⁰Be/Be on L and forecast on which energy range better data would be helpful for future L improvements.
Methods: We used USINE V3.5 for the propagation of nuclei, and e⁺ were calculated with the pinching method.
Results: The current AMS-02 Be/B (∼3% precision) and ACE-CRIS ¹⁰Be/Be (∼10% precision) data bring similar and consistent constraints on L. The AMS-02 Be/B data alone constrain L = 5_-2⁺³ kpc at a 68% confidence level (spanning different benchmark transport configurations), a range for which most models do not overproduce positrons. Future experiments need to deliver percent-level accuracy on ¹⁰Be/⁹Be anywhere below 10 GV to further constrain L.
Conclusions: Forthcoming AMS-02, HELIX, and PAMELA ¹⁰Be/⁹Be results will further test and possibly tighten the limits derived here. Elemental ratios involving radioactive species with different lifetimes (e.g. Al/Mg and Cl/Ar) are also awaited to provide complementary and robuster constraints.