Anti-helium from dark matter annihilations

Abstract

Galactic Dark Matter (DM) annihilations can produce cosmic-ray anti-nuclei via the nuclear coalescence of the anti-protons and anti-neutrons originated directly from the annihilation process. Since anti-deuterons have been shown to offer a distinctive DM signal, with potentially good prospects for detection in large portions of the DM-particle parameter space, we explore here the production of heavier anti-nuclei, specifically antihelium. Even more than for anti-deuterons, the DM-produced anti-He flux can be mostly prominent over the astrophysical anti-He background at low kinetic energies, typically below 3-5 GeV/n. However, the larger number of anti-nucleons involved in the formation process makes the anti-He flux extremely small. We therefore explore, for a few DM benchmark cases, whether the yield is sufficient to allow for anti-He detection in currentgeneration experiments, such as Ams-02. We account for the uncertainties due to the propagation in the Galaxy and to the uncertain details of the coalescence process, and we consider the constraints already imposed by anti-proton searches. We find that only for very optimistic configurations might it be possible to achieve detection with current generation detectors. We estimate that, in more realistic configurations, an increase in experimental sensitivity at low kinetic energies of about a factor of 500-1000 would allow to start probing DM through the rare cosmic anti-He production.

Signatures of Majorana dark matter with t-channel mediators

“…81,82 These channels are particularly interesting due to the very small background flux of antideuterons 83,84 and antihelium 81,82 expected at the energies relevant for experiments. In fact, the expected flux from spallations of cosmic rays on the interstellar medium lies more than three orders of magnitude below the Table 2.…”

Aspects of WIMP Dark Matter Searches at Colliders and Other Probes

“…Mass numbers A > 2 are suppressed essentially due to the reduced probability for a large number of nucleons to coalesce. For this reason, only anti-3 He seems to be a promising candidate [282,283].…”

Production of cosmic-ray antinuclei in the Galaxy and background for dark matter searches

“…Using cross-sections presented in [6,7,9], we calculated the production of several isotopes such as 2 H, 3 He, 6,7 Li, 7,9,10 Be, and 10,11 B from fragmentation of C-N-O, Si, and Fe. We implemented dedicated algorithms to compute thep andn production from p-p, p-He, He-p, and He-He collisions [10].…”

“…Then, we used an improved nuclear coalscence model to evaluate the production of d={n,p} and He [11]. Antihelium production includes 3 H={n,n,p} and 3 He={n,p,p}. The SNR injection spectrum of primary CRs is calculated from the diffusive-shock-acceleration equation.…”

“…The detection of antinuclei d and He is the next milestone in CR physics. DM annihilation processes into d and He particles may generate an observable excess in their spectrum [2,3,4]. In particular, at energy below a few GeV, the astrophysical background is kinematically suppressed while DM signals peak in this energy window according to several models of DM annihilation.…”