Effects of the Sagittarius Dwarf Tidal Stream on Dark Matter Detectors

The Sagittarius dwarf tidal stream may be showering dark matter onto the solar neighborhood, which can change the results and interpretation of direct detection searches for weakly interacting massive particles (WIMPs). Stars in the stream may already have been detected in the solar neighborhood, and the dark matter in the stream is (0.3–25)% of the local density. Experiments should see an annually modulated steplike feature in the energy recoil spectrum that would be a smoking gun for WIMP detection. The total count rate in detectors is not a cosine curve in time and peaks at a different time of year than the standard case.

Figure 1

Count rate of 60 GeV WIMPs over the course of a year in a NaI detector such as DAMA due to the halo alone as well as the sum of the halo and stream, for our reference direction for stream densities that are 4% and 20% of the halo, and in the 2–6 keVee bin.

Figure 2

Count rate of 60 GeV WIMPs in a NaI detector such as DAMA vs recoil energy. The dotted lines show the count rate from galactic (isothermal) halo WIMPs alone. The solid and dashed lines show the step in the count rate if we include the Sgr stream WIMPS. The plot assumes that the stream contributes an additional 20% of the local galactic halo density and comes from our reference direction. The solid and dashed lines are for July 15 and January 14, respectively, the dates of maximum and minimum count rate for the stream.