Detectability of Weakly Interacting Massive Particles in the Sagittarius Dwarf Tidal Stream

Tidal streams of the Sagittarius dwarf spheroidal galaxy (Sgr) may be showering dark matter onto the solar system and contributing ∼(0.3–25)% of the local density of our Galactic Halo. If dark matter consists of WIMPs, the extra contribution from the stream gives rise to a step-like feature in the energy recoil spectrum in direct dark matter detection. For our best estimate of stream velocity (300 km/sec) and direction (the plane containing the Sgr dwarf and its debris), the count rate is maximum on June 28 and minimum on December 27 (for most recoil energies), and the location of the step oscillates yearly with a phase opposite to that of the count rate. The energy of the step should be above the threshold of the DAMA/NaI detector. Thus the WIMP signal from the Sgr stream may already be present in the DAMA/NaI data (at a level up to 100σ), and may be useful to help establish the interpretation of the DAMA annual modulation as due toWIMPs. In addition, the WIMP parameters that best fit the data would need to be recalculated. The stream may explain the discrepancy between DAMA results and data from other experiments. In the CDMS experiment, for 60 GeV WIMPs, the location of the step oscillates between 35 and 42 keV, and for the most favorable stream density, the stream should be detectable at the 11σ level in four years of data with 10 keV energy bins. Planned large detectors like XENON, CryoArray and the directional detector DRIFT may also be able to identify the Sgr stream.