A Dark Matter Hurricane: Measuring the S1 Stream with Dark Matter Detectors

TL;DR

This paper investigates how the S1 stellar stream, with a significant dark matter component, affects detection prospects for WIMP and axion dark matter detectors, highlighting potential improvements in sensitivity and distinguishability.

Contribution

It provides the first detailed analysis of the S1 stream's impact on both WIMP and axion dark matter detection methods, emphasizing the stream's detectability even at low densities.

Findings

S1 stream enhances high-energy nuclear recoils in WIMP detectors.

Multi-ton xenon detectors can distinguish S1 from the halo for certain masses.

Axion haloscopes have the greatest potential sensitivity to S1.

Abstract

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