Detectability of weakly interacting massive particles in the Sagittarius dwarf tidal stream

Abstract

Tidal streams of the Sagittarius dwarf spheroidal galaxy (Sgr) may be showering dark matter onto the solar system and contributing $\ensuremath{\sim}(0.3--23)%$ of the local density of our galactic halo. If the Sagittarius galaxy contains dark matter in the form of weakly interacting massive particles (WIMPs), the extra contribution from the stream gives rise to a steplike feature in the energy recoil spectrum in direct dark matter detection. For our best estimate of stream velocity (300 km/s) 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. 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 $11\ensuremath{\sigma}$ 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.