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

¹ LPSC, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, 38026 Grenoble, France
e-mail: david.maurin@lpsc.in2p3.fr
² Instituto de Física Teórica UAM/CSIC, Calle Nicolás Cabrera 13-15, Cantoblanco 28049 Madrid, Spain
³ Niels Bohr International Academy & Discovery Center, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
⁴ LUPM, CNRS & Université de Montpellier (UMR-5299), Place Eugène Bataillon, 34095 Montpellier Cedex 05, France
e-mail: julien.lavalle@umontpellier.fr
⁵ LAPTh, Université Savoie Mont Blanc & CNRS, 74941 Annecy Cedex, France
e-mail: pierre.salati@lapth.cnrs.fr

Received: 1 April 2020
Accepted: 14 May 2020

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.