Speaker
Description
Recently, we proposed paleo-detectors as a method for the direct detection of Weakly Interacting Massive Particle (WIMP) dark matter. In paleo-detectors, one would search for the persistent traces left by dark matter--nucleon interactions in ancient minerals. Thanks to the large integration time of paleo-detectors, relatively small target masses suffice to obtain exposures much larger than what is feasible in the conventional direct detection approach. In order to suppress backgrounds induced by radioactive contaminants such as uranium, we propose to use minerals found in marine evaporites or in ultra-basic rocks. For sufficiently radiopure target materials obtained from boreholes deep enough to avoid cosmogenic backgrounds, we identify (broadly speaking) two different background regimes. For low-mass WIMPs with masses $m_\chi < 10\,$GeV, the largest contribution to the background budget comes from nuclear recoils induced by coherent scattering of solar neutrinos. For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons arising from trace amounts of radioactivity. We consider fast neutrons from both spontaneous fission and ($\alpha$,n) reactions induced by the $\alpha$-particles produced in the decay chains of heavy radioactive contaminants. Even after accounting for these backgrounds, we demonstrate that paleo-detectors could potentially be sensitive to much of the remaining WIMP parameter space.
