In this era of precision cosmology, measurements suggest that ordinary matter (protons and neutrons) represents only a fraction of the total matter density in the Universe. The rest, whose effect we can see only gravitationally, is unknown in its nature and is termed Dark Matter. Particle physics models suggest that dark matter is composed of relic Weakly Interacting Massive Particles (WIMPs) left over from the Big Bang. Experimental efforts to directly detect WIMPs are challenging due to the predicted small interaction probabilities and the existence of large backgrounds that mimic the expected signal. However, a number of unique dark matter signatures exist that can be used to discriminate against backgrounds and decisively identify WIMP interactions. The largest and most robust signature is the predicted dependence of the WIMP flux on the Sun-Earth velocity through the galaxy, yielding a day-night modulation of the nuclear recoil direction in the laboratory. Of current searches with directional detectors, the Directional Recoil Identification From Tracks (DRIFT) experiment is a leader, having a decade of experience. The intellectual merit of this proposal resides in DRIFT's unique and powerful capabilities being brought to bear on one of the most important questions in science today.
These advances in background rejection, combined with the fact that further limit setting capabilities are hampered by the small volume of DRIFT-II, suggest that DRIFT should scale-up. This award will enable the collaboration to continue running DRIFT-II in the Boulby mine in England. In addition to running DRIFT-IId, these funds will provide hardware for a second detector, DRIFT-IIe.
Broader impacts of this work include the training of a diverse set of undergraduates and graduate students (including underrepresented minorities) in increasingly rare small-scale experiments, giving them exposure to a wide range of hardware and software experience. Finally, the DRIFT detector technology has promising applications to Homeland Security and double-beta decay experiments.