Dark matter hurricane: Measuring the S1 stream with dark matter detectors

Abstract

The recently discovered S1 stream passes through the Solar neighbourhood on a\nlow inclination, counter-rotating orbit. The progenitor of S1 is a dwarf galaxy\nwith a total mass comparable to the present-day Fornax dwarf spheroidal, so the\nstream is expected to have a significant DM component. We compute the effects\nof the S1 stream on WIMP and axion detectors as a function of the density of\nits unmeasured dark component. In WIMP detectors the S1 stream supplies more\nhigh energy nuclear recoils so will marginally improve DM detection prospects.\nWe find that even if S1 comprises less than 10% of the local density, multi-ton\nxenon WIMP detectors can distinguish the S1 stream from the bulk halo in the\nrelatively narrow mass range between 5 and 25 GeV. In directional WIMP\ndetectors such as CYGNUS, S1 increases DM detection prospects more\nsubstantially since it enhances the anisotropy of the WIMP signal. Finally, we\nshow that axion haloscopes possess by far the greatest potential sensitivity to\nthe S1 stream. Once the axion mass has been discovered, the distinctive\nvelocity distribution of S1 can easily be extracted from the axion power\nspectrum.\n