Implications of the first AMS-02 measurement for dark matter annihilation and decay

Abstract

In light of the first measurement of the positron fraction by the AMS-02 experiment, we perform a detailed global analysis on the interpretation of the latest data of PAMELA, Fermi-LAT, and AMS-02 in terms of dark matter (DM) annihilation and decay in various propagation models. The allowed regions for the DM particle mass and annihilation cross section or decay life-time are obtained for channels with leptonic final states: $2e$, $2μ$, $2τ$, $4e$, $4μ$ and $4τ$. We show that for the conventional astrophysical background the AMS-02 positron fraction data alone favour a DM particle mass $\sim 500 \ (800)$ GeV if DM particles annihilate dominantly into $2μ\ (4μ)$ final states, which is significantly lower than that favoured by the Fermi-LAT data of the total flux of electrons and positrons. The allowed regions by the two experiments do not overlap at a high confidence level ($99.99999\%$C.L.). We consider a number of propagation models with different halo height $Z_{h}$, diffusion parameters $D_{0}$ and $δ_{1/2}$, and power indices of primary nucleon sources $γ_{p1/p2}$. The normalization and the slope of the electron background are also allowed to vary. We find that the tension between the two experiments can be only slightly reduced in the propagation model with large $Z_{h}$ and $D_{0}$. The consistency of fit is improved for annihilation channels with $2τ$ and $4τ$ final states which favour TeV scale DM particle with large cross sections above $\sim 10^{-23} \text{cm}^3\text{s}^{-1}$. In all the considered leptonic channels, the current data favour the scenario of DM annihilation over DM decay. In the decay scenario, the charge asymmetric DM decay is slightly favoured.