Dark Matter Annihilation Can Produce a Detectable Antihelium Flux through ${\overline{\mathrm{\Lambda }}}_b$ Decays

Recent observations by the Alpha Magnetic Spectrometer (AMS-02) have tentatively detected a handful of cosmic-ray antihelium events. Such events have long been considered as smoking-gun evidence for new physics, because astrophysical antihelium production is expected to be negligible. However, the dark-matter-induced antihelium flux is also expected to fall below current sensitivities, particularly in light of existing antiproton constraints. Here, we demonstrate that a previously neglected standard model process—the production of antihelium through the displaced-vertex decay of ${\overline{\mathrm{\Lambda }}}_b$-baryons—can significantly boost the dark matter induced antihelium flux. This process can entirely dominate the production of high-energy antihelium nuclei, increasing the rate of detectable AMS-02 events by 2 orders of magnitude.

Figure 1

Antihelium injection spectrum from dark matter annihilation using the pythia event generator. The prompt and ${\overline{\mathrm{\Lambda }}}_b$-induced contributions are shown separately. The antihelium flux from ${\overline{\mathrm{\Lambda }}}_b$ decays exceeds that of prompt events by nearly a factor of 2, and entirely dominates the production of high-energy antihelium.

Figure 2

(Left) Antihelium flux from dark matter annihilation with $⟨\sigma v⟩=2\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$, for event generators described in the text. The AMS-02 10-year sensitivity (orange) is derived from Refs. [46, 47] (see Supplemental Material [28]). These results show that ${\mathrm{\Lambda }}_b$ decays significantly boost the number of detectable antihelium events. (Right) Same, but for dark matter that annihilates through 14 GeV light mediators. For this model, pythia does not predict any prompt events (all events are produced by ${\mathrm{\Lambda }}_b$ decay).

Figure 3

Same as Fig. 2, but for antideuterons instead of antihelium. The AMS-02 and GAPS antideuteron sensitivities are taken from Ref. [10].